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1. AU2001065451 - Methods for providing safe local anaesthesia

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Methods for Providing Safe Local Anaesthesia
Field of the Invention
The present invention is related to methods for providing local anaesthesia with greatly enhanced safety and reduced risk of toxicity. In particular, methods are provided for increasing the safety and reducing the risk of toxic reactions and side effects by the use of biocompatible, biodegradable, controlled release formulations for the administration of local anaesthetics in a form that provides greatly enhanced safety.
Background of the Invention
Local anaesthetics act to produce a loss of sensation and/or motor function in the localised area of administration in the body. Ideally, a local anaesthetic does not cause local tissue irritation and does not cause permanent damage to the nerve tissue to which it is applied, ie., the local anaesthesia should be non-toxic and reversible. It is also desirable for a local anaesthetic to have low systemic toxicity, since these agents are ultimately absorbed systemically, where sufficient blood and/or tissue levels can cause cardiac toxicity. Further, there is the possibility that such agents could accidentally be injected into a blood vessel or ingested, greatly increasing the risk of untoward effects.
The art has recognised the need for compositions and methods for providing safe local anaesthesia with rapid onset and a reasonably prolonged duration, eg., up to eight hours of local anaesthesia. However, methods and formulations heretofore available for providing local anaesthesia, particularly local anaesthesia lasting as long as 8h, place the patient at risk for local and systemic toxic effects, such as an increased risk of neurolysis and tissue necrosis and systemic toxicity due to redistribution of excess locally administered local anaesthetic into the general circulation.
The duration of action of a local anaesthetic is proportional to the time during which it is in actual contact with the nervous tissues. Consequently, procedures or formulations that maintain localisation of the drug at the nerve greatly prolong anaesthesia. One approach that has heretofore been employed is to combine a vasoconstrictor agent such as epinephrine with a local anaesthetic. However, this approach to increasing potency and/or duration of action is limited by the risk of causing tissue necrosis due to excessive localised vasoconstriction.
Another approach was based on analysis of the structure-activity relationship of the local anaesthetic compounds. Structure-activity analysis for local anaesthetic compounds indicates that relative increases in hydrophobicity are accompanied by relative increases in the potency and in duration of action of these agents. Unfortunately, relative increases in hydrophobicity also elevate the toxic tissue effects, therefore resulting in no effective improvement in the therapeutic index, ie., no increase in safety will result from this approach. The most recent example of this approach is NaropinTM (ropivacaine, Astra Pharmaceuticals), which was reported to be a safer (relative to bupivacaine solution) long acting amide local anaesthetic for injection. However, one condition for the approval of ropivacaine is that the package insert warn against rapid injection in large doses, since it o* 'is expected to share the risk of cardiac arrhythmias, cardiac/circulatory arrests and death if inadvertently injected intravenously (F-D-C Reports ."The Pink Sheet", December 18, 1995). Thus, there remains a need in the art for methods and formulations enhancing the safety of administration of local anaesthetics.
LibC/447323d1 speci Different methods and formulations are known in the art for administration of local anaesthetics.
For example, US 4725442 and 4622,219 are directed to microdroplets of methoxyflurane-containing microdroplets coated with a phospholipid prepared by sonication, which are suitable for intradermal or intravenous injection into a patient for inducing local anaesthesia. Such microdroplets are said to provide long-term local anaesthesia when injected intradermally, giving a duration of anaesthesia considerably longer than the longest acting conventional local anaesthetic (bupivacaine). W094/05265 describes improved biodegradable controlled release systems consisting of a polymeric matrix incorporating a local anaesthetic for the prolonged administration of the local anaesthetic agent. The devices are selected on the basis of their degradation profiles: release of the topical anaesthetic in a linear, controlled manner over the period of preferably two weeks and degradation in vivo with a half-life of less than six months, more preferably two weeks, to avoid localised inflammation. The disclosure states that an anti-inflammatory can be incorporated into the polymer with the local anaesthetic to reduce encapsulation for optimal access of drug to its site of action. The anti-inflammatories that are said to be useful include steroids such as dexamethasone, cortisone, prednisone, and others routinely administered orally or by injection.
However, methods have not previously been known to provide for safe, regulated administration of a local anaesthetic resulting in greatly reduced toxicity and an enhanced therapeutic index to provide both short term and long term sensory and motor anaesthesia to a local area of a patient in need of such treatment.
Objects of the Invention
Accordingly, it is therefore an object of the present invention to provide compositions for providing safe local anaesthesia with a substantially reduced risk of toxic reactions and/or untoward side effects.
It is a further object of the present invention to provide methods for providing a safe local
25 anaesthesia which effectively controls acute and chronic pain, including post-traumatic and post-:operative pain.
Summary of the Invention
In accordance with the above-mentioned objects and others, the invention is related to the surprising discovery that controlled release formulations, which provide prolonged release of local anaesthetic agents in vitro, ranging from several hours up to, eg., two days or more, are unable to provide more than about 8h of local anaesthesia, in vivo. Thus, the ordinary artisan would not expect such formulations to be any more useful than a conventional immediate release local anaesthetic formulation, eg., bupivacaine with epinephrine, for inducing local anaesthesia.
However, Applicants have now unexpectedly discovered that local anaesthetic incorporated into, eg., controlled release microspheres, provides the expected prolonged release of local anaesthetic only in vitro. Instead, for unknown reasons, the formulations fail to provide prolonged local anaesthetic when tested in vivo, ie., in animals.
In a further surprising discovery, it has been found that controlled release local anaesthetic formulations prepared, eg., in the form of injectable microspheres, provide both immediate local anaesthesia after administration, and provide greatly enhanced safety. Thus, the controlled release
LibC/447323d1speci formulations according to the invention release enough local anaesthetic, in vivo, to provide a normal onset of local anaesthesia. However, in an unexpected benefit, the same controlled release local anaesthetic formulations fail to cause the expected toxic results when injected into test animals in what would otherwise be toxic amounts. Thus, the present invention provides methods and compositions for inducing local anaesthesia with a substantially reduced risk of untoward toxicity and undesirable effects.
The controlled release formulation can be formed into slabs, pellets, microparticles, microspheres, microcapsules, spheroids and pastes. Preferably, the formulation is in a form suitable for suspension in isotonic saline, physiological buffer or other solution acceptable for injection into a patient.
The invention further provides methods for inducing localised anaesthesia by implanting, inserting or injecting a controlled release formulation, eg., in the form of injectable microspheres loaded with a local anaesthetic in sustained release form, into a site at or adjacent to a nerve or nerves innervating a body region to provide local anaesthesia. Thus, the safe local anaesthetic formulation according to the invention can be injected, infiltrated or implanted at a site in a patient where the local anaesthetic agent is to be released. Optionally, the safe local anaesthetic formulation can also be applied topically, eg., to skin and/or mucosal surfaces.
Further aspects of the invention are directed to a method of treating a patient in need of a surgical procedure, comprising placing a safe local anaesthetic form in proximity to a nerve or nerves at the surgical site.
Therefore, the present invention provides for safe regional local anaesthesia at a site in a patient, by administering at the site a local anaesthetic incorporated in a biocompatible, biodegradable, controlled release formulation where the site of administration is located at or adjacent to a nerve or nerves innervating a region of the patient to be so anaesthetised. Further, the local anaesthetic is present in a concentration effective to safely achieve sensory or motor local :anaesthesia with reduced toxicity, and the local anaesthetic is released at a rate effective to safely achieve sensory or motor local anaesthesia. In one aspect, the method of the invention provides for at least a portion of the local anaesthetic in immediate release form.
In one preferred embodiment, the method provides for preparing the controlled release form as 30 a plurality of microspheres, suspending the microspheres in a pharmaceutically acceptable medium for injection, and injecting said microspheres at a site in a patient, for example, in proximity to a nerve to be anaesthetised. The local anaesthetic can be incorporated into the formulation, such as, for example the plurality of controlled release microspheres at a percent loading of 0.1% to 90% and in a preferred embodiment, at a loading ranging from about 20wt% to about 80wt%, and in a more preferred embodiment, at a percent loading ranging from about 70wt% to about
Although any pharmaceutically acceptable local anaesthetic may be employed according to the method of the invention, the local anaesthetic is preferably selected from bupivacaine, dibucaine, Soprocaine, chloroprocaine, prilocaine, mepivacaine, etidocaine, tetracaine, lidocaine and xylocaine, and salts, derivatives or mixtures thereof In a more preferred embodiment, the local anaesthetic is bupivacaine. The method can be conducted with bupivacaine HCI, bupivacaine free base and/or
LibC/447323dl speci mixtures thereof. While the artisan will understand that the dose will vary according to the size and weight of the patient and the number of nerves to be blocked and/or treated, the bupivacaine is administered in a dose ranging from 5 through 450mg/kg of a patient. Alternatively, bupivacaine is administered according to the invention in a dose ranging from about 0.5mg to about 200mg or more, depending upon the aforementioned factors. Preferably, bupivacaine is administered in a dose ranging from about 1 to about 50mg or more, and more preferably, bupivacaine is administered in a dose ranging from about 1 to about 20mg, depending upon the above listed factors. Of course, the artisan will appreciate that the dosage ranges of other art-known local anaesthetics can be determined relative to the potency of bupivacaine.
In further embodiment, the method of the invention is conducted with a local anaesthetic in a biocompatible, biodegradable controlled release form such that the percent release of said local anaesthetic in vitro, is from about 10 to about 60% release after 24h, from about 20 to about 80% after 48h, and from about 40 to about 100% release after 72h, administered at a site in a patient in a dose of controlled release form effective to safely achieve a reversible local anaesthesia at the site.
The method of the invention may also be conducted by administering a formulation prepared as a unit dosage of the controlled release formulation comprising, in a container, a sufficient amount of the formulation to induce local anaesthesia in at least one patient. In one embodiment, the unit dosages are sterile and lyophilised. Alternatively, the unit dosages are sterile and prepared as a suspension in a solution acceptable for injection into a patient.
The controlled release local anaesthetic dosage form may be injected and/or infiltrated, at the site where the anaesthetic is to be released. This can be prior to surgery, at the time of surgery, or following removal (discontinuation) or reversal of a systemic anaesthetic.
According to the invention, an effective local anaesthetic dose of the biocompatible, biodegradable, controlled release formulation according to the invention will, when injected into the patient intravenously, fail to induce a toxic reaction or alternatively, be much less likely to induce a toxic reaction relative to the toxicity of bupivacaine HCI or bupivacaine free base. In another aspect, when the local anaesthetic is bupivacaine an intravenously administered dose, measured by the amount required to produce an effective local anaesthesia, of the biocompatible, biodegradable, controlled release formulation will be unable to produce a bupivacaine blood plasma level of about 1600ng/mL or, alternatively, no more than about 1200ng/mL of plasma bupivacaine. In a further aspect, when the local anaesthetic is bupivacaine, an intravenously administered dose, measured by the amount required to produce an effective local anaesthesia, of the biocompatible, biodegradable, controlled release formulation will be unable to produce a bupivacaine blood plasma higher than from about 200 to about 650ng/mL.
Examples demonstrate the greatly enhanced safety and greatly reduced toxicity provided by the methods and formulations according to the invention.
Brief Description of the Drawings
The following drawings are illustrative of embodiments of the invention and are not meant to limit the scope of the invention as encompassed by the claims.
Fig.  1  is a  graphical  representation   of  the  dissolution  data  obtained  for  Examples  1-3,
LibC/447323d1speci Fig. 2 is a graphical representation comparing the dissolution data obtained for Example 6 (spray-drying process) and Example 9 (solvent extraction process); and
Fig. 3 is a graphical representation of the dissolution data obtained for Examples 4-(spraydrying process) and Examples 7-8 (solvent extraction process).
Fig. 4 is a graphical representation of the bupivacaine release rate from PLA 100, PLGA 65:35 and 75:25.
Detailed Description
Accordingly, methods and formulations according to the invention unexpectedly provide substantially safer methods and formulation for inducing local anaesthesia at a desired site in a patient (human or animal). Controlled release formulations of local anaesthetics have surprisingly been found to provide controlled and prolonged release of incorporated local anaesthetic in vitro, but to provide normal durations of local anaesthesia in test animals. Thus, Applicants' discovery that the formulations and methods according to the invention nevertheless provide substantially safer local anaesthesia is surprisingly unexpected. Applicants have discovered that controlled release formulations according to the invention surprisingly provide essentially normal, not delayed, onset of local anaesthesia where administered, but does avoid the release of sufficient incorporated local anaesthetic in toxic amounts, even when, eg., times an otherwise lethal amount of the anaesthetic is administered.
Thus, methods for providing local anaesthesia having greatly enhanced safety are provided which are achieved by the administration of formulations for the safe and regulated delivery of a local anaesthetic agent to a targeted area. These methods can be used for the safe management of various forms of acute pain, such as dental pain, or for persistent pain, such as postoperative pain, sympathetically maintained pain, or certain forms of chronic pain such as the pain associated with many types of cancer. These systems may also be used for blockade of nociceptive pathways (afferent and efferent) in patients with acute pancreatitis, ileus, or other visceral disorders. :As used herein, the term "local anaesthetic agent" means any drug which provides local numbness and/or analgesia. Examples of local anaesthetic agents which can be used include bupivacaine, ropivacaine, dibucaine, procaine, chloroprocaine, prilocaine, mepivacaine, etidocaine, tetracaine, lidocaine, and xylocaine, and mixtures thereof The local anaesthetic can be in the form of a 30 salt, for example, the hydrochloride, bromide, acetate, citrate, carbonate or sulfate. More preferably, the local anaesthetic agent is in the form of a free base. The free base provides a slower initial release and avoids an early "dumping" of the local anaesthetic at the injection site. Preferred local anaesthetic agents include, eg., bupivacaine. Bupivacaine is a particularly long acting and potent local anaesthetic agent when incorporated into a PLAM or other controlled release formulation. Its other advantages include sufficient sensory anaesthesia without significant motor blockade, lower toxicity, and wide availability. Anaesthetics typically administered systematically may also be used in those cases where *the means of administration results only in a local effect, rather than systemic.
S°The term "local anaesthetic" may also encompass, pursuant to the definitions provided herein, a drug of a different class than those traditionally associated with local anaesthetic properties,
LibC/447323dspec including but not limited to morphine, fentanyl, and agents which, for example, can provide regional blockade of nociceptive pathways (afferent and/or efferent).
The terms "safe" or "safety" as used herein describes a substantial reduction in the risk of a toxic reaction or effect resulting from administration of a local anaesthetic by the methods of the present invention compared to the risk of a toxic reaction or effect resulting from the administration of a local anaesthetic agent administered by a method not using a local anaesthetic incorporated into a controlled release formulation for regulated release at the site of action. For example, toxicity to bupivacaine is associated with plasma concentrations in excess of 1600ng/mL. When controlled release bupivacaine is administered according to the methods of the invention, even at doses higher than those required to achieve prolonged anaesthesia, plasma bupivacaine doses not exceed 200 to 650ng/mL.
As used herein, the term "patient" broadly refers to any animal that is to be treated with the compositions and by the methods herein disclosed. The methods of the invention using the disclosed local anaesthetic dosage forms can provide localised pain blockade to any animal, eg., any vertebrate, which it is desired to so anaesthetise, in particular, the disclosed methods and compositions will find use in veterinary practice and animal husbandry for, eg., birds and mammals, wherever prolonged local anaesthesia is convenient or desirable. In a preferred embodiment, the term "patient" includes humans in need of or desiring local anaesthesia of greatly enhanced safety.
Any pharmaceutically acceptable formulation suitable for local implantation, infiltration or injection in proximity to a nerve that is able to provide a safe and controlled release of an effective amount of a local anaesthetic agent and/or a glucocorticoid agent may be employed to provide for safe local anaesthesia as needed. Art known slow release formulations and/or carriers, eg., emulsions, liposomes, gels, suspensions, biocompatible polymers and gum matrices may be employed. Slow release formulations according to the invention also include, eg., specially coated pellets, polymer formulations or matrices for surgical insertion or controlled release microparticles or :microspheres for implantation, insertion or injection, wherein the slow release of the active medicament is brought about through controlled diffusion out of the formulation and/or selective breakdown of the coating of the preparation, or selective breakdown of a polymer matrix, if present. The safety enhancing methods according to the invention may be provided in conjunction with any implantable, insertable or injectable system known in the art, including but not limited to micro spheres, microcapsules, gels, pastes, implantable rods, pellets, plates or fibres, and the like (generically referred to as "substrates").
In a preferred embodiment, the slow release formulation is prepared as microspheres in a size distribution range suitable for local injection. The diameter and shape of the microspheres or other particles can be manipulated to modify the release characteristics. For example, larger diameter microspheres will typically provide slower rates of release and reduced tissue penetration and smaller diameters of microspheres will produce the opposite effects, relative to microspheres of different mean diameter but of the same composition. In addition, other particle shapes, such as, for example, cylindrical shapes, can also modify release rates by virtue of the increased ratio of surface area to mass inherent to such alternative geometrical shapes, relative to a spherical shape. The diameter of
LibC/447323d1speci injectable microspheres are in a size range, for example, from about 5 m to about 200 m in diameter. In a more preferred embodiment, the microspheres range in diameter from about 20 to about 120 Pn. A wide variety of biodegradable materials may be utilised to provide the controlled 25 release of the local anaesthetic. Any pharmaceutically acceptable biodegradable polymers known to those skilled in the art may be utilised.
The controlled release material should be biocompatible and be degraded, dissolved or absorbed in situ in a safe and pharmaceutically acceptable manner so that the material is removed from the injection or implantation site by natural tissue processes and in a suitable amount of time, eg., less than one year, preferably less than 6 months, and most preferably in less than one month. In any event, the carrier may be removed by local tissue processes without causing untoward local tissue reaction, or systemic or local toxicity. In the case of polymeric materials, biocompatibility is enhanced by preparing the polymeric materials in a pharmaceutically acceptable manner, ie., employing purification techniques well known to the art, eg., recrystallisation of either the monomers forming the polymer and/or the polymer and other techniques for producing materials for implantation or injection into living tissue.
Suitable biodegradable polymers can be utilised as the controlled release material. The polymeric material may comprise a polylactide, a polyglycolide, a poly(lactide-co-glycolide), a polyanhydride, a polyorthoester, polycaprolactones, polyphosphazenes, polysaccharides, proteinaceous polymers, soluble derivatives of polysaccharides, soluble derivatives of proteinaceous polymers, polypeptides, polyesters, and polyorthoesters. The polysaccharides may be poly-1,4-glucans, eg., starch glycogen, amylose, amylopectin, and mixtures thereof. The biodegradable hydrophilic or hydrophobic polymer may be a water-soluble derivative of a poly-1,4-glucan, including hydrolysed amylopectin, hydroxyalkyl derivatives of hydrolysed amylopectin such as hydroxyethyl starch (HES), hydroxyethyl amylose, dialdehyde starch, and the like. Preferred controlled release materials which are useful in the formulations of the invention include the polyanhydrides, co-polymers of lactic acid and glycolic acid wherein the weight ratio of lactic acid to glycolic acid is no more than 4:1 80wt% or less lactic acid to 20wt% or more glycolic acid), and polyorthoesters containing a catalyst or degradation enhancing compound, for example, containing at least 1wt% anhydride catalyst such as maleic anhydride. Other useful polymers include protein polymers such as gelatin and fibrin and polysaccharides such as hyaluronic acid. Since polylactic acid takes at least one year to degrade in vivo, this polymer should be utilised by itself only in circumstances where such a degradation rate is desirable or acceptable.
Commercially available polymers include, for example, poly(d,l-lactic-co-glycolic acid) and preferably 50:50 poly lactic co-glycolic acid having a mole composition of 50% lactide and 50% glycolide. Other suitable commercially available products include 65:35 DL, 75:25 DL, 85:15 DL and poly(d,l-lactic acid) (d,l-PLA). Poly(lactide-co-glycolides) are commercially available, for example, from Boehringer Ingelheim (Germany) under its Resomer@ mark, eg., PLGA 50:50 (Resomer RG 502), PLGA 75:25 (Resomer RG 752) and 30 d,I-PLA (Resomer RG 206), and from Birmingham Polymers (Birmingham, Alabama). These copolymers are available in a wide range of molecular weights and ratios of lactic to glycolic acid.
LibC/447323d1speci Proteinaceous polymers may also be used. Proteinaceous polymers and their soluble derivatives include gelation biodegradable synthetic polypeptides, elastin, alkylated collagen, alkylated elastin, and the like. Biodegradable synthetic polypeptides include poly-(N-hydroxyalkyl)-L-asparagine, poly-(N-hydroxyalkyl)-L-glutamine, copolymers of N-hydroxyalkyl-L-asparagine and N-hydroxyalkyl-L-glutamine with other amino acids. Suggested amino acids include L-alanine, L-lysine, L.-phenylalanine, L-valine, L-tyrosine, and the like.
In embodiments where the biodegradable polymer comprises a gel, one such useful polymer is a thermally gelling polymer, eg., polyethylene oxide, polypropylene oxide (PEO-PPO) block copolymer such as Pluronic@ F127 from BASF Wyandotte. In such cases, the local anaesthetic formulation may be injected via syringe as a free-flowing liquid, which gels rapidly above 30°C when injected into a patient). The gel system then releases a steady dose of local anaesthetic at the site of administration.
In additional embodiments of the invention, the controlled release material, which in effect acts as a carrier for the local anaesthetic, can further include a bioadhesive polymer such as pectins (polygalacturonic acid), mucopolysaccharides (hyaluronic acid, mucin) or non-toxic lectins or the polymer itself may be bioadhesive, eg., polyanhydride or polysaccharides such as chitosan. Further, the pharmacokinetic release profile of these formulations may be first order, zero order, bi- or multiphasic, to provide the desired reversible local anaesthetic effect over the desired time period.
Definitions or further descriptions of any of the foregoing terminology are well known in the art and may be found by referring to any standard biochemistry reference text such as "Biochemistry" by Albert L. Lehninger, Worth Publishers, Inc. and "Biochemistry" by Lubert Stryer, W.H. Freeman and Company, both of which are hereby incorporated by reference. The aforementioned biodegradable hydrophobic and hydrophilic polymers are particularly suited for the methods and compositions of the present invention by reason of their characteristically low human toxicity and virtually complete 25 biodegradability.
The substrates of the presently described formulations are preferably manufactured using a :i method that evenly disperses the local anaesthetic throughout the formulation, such as emulsion preparation, solvent casting, spray drying or hot melt, rather than a method such as compression moulding. A desired release profile can be achieved by using a mixture of polymers having different release rates and/or different percent loading of local anaesthetic and/or augmenting agent, for example, polymers releasing in one day, three days, and one week, so that linear release is achieved even when each polymer per se does not release linearly over the same time period. In addition, a mixture of microspheres having one or more different local anaesthetic agents, having the same or different controlled release profile, can be utilised to provide the benefits of different potencies and spectrum of activity during the course of treatment.
Methods for manufacture of microspheres are well known and are typified in the following examples. Examples of suitable methods of making microspheres include solvent evaporation, phase separation and fluidised bed coating.
In solvent evaporation procedures, the local anaesthetic agent, if soluble in organic solvents, may be entrapped in the biodegradable polymer by dissolving the polymer in a volatile organic
LibC/447323d1speci solvent, adding the drug to the organic phase, emulsifying the organic phase in water which contains less than 2% polyvinyl alcohol, and finally removing the solvent under vacuum to form discrete, hardened monolithic microspheres.
Phase separation microencapsulation procedures are suitable for entrapping water-soluble agents in the polymer to prepare microcapsules and microspheres. Phase separation involves coacervation of the polymer from an organic solvent by addition of a nonsolvent such as silicone oil. In fluidised bed coating, the drug is dissolved in an organic solvent along with the polymer. The solution is then processed, eg., through a Wurster air suspension coater apparatus to form the final microcapsule product.
The biodegradable controlled release materials may be used in order to prepare controlled release local anaesthetic implants. The implants may be manufactured, eg., by compression moulding, injection moulding, and screw extrusion, whereby the local anaesthetic agent is loaded into the polymer. Implantable fibres can be manufactured, eg., by blending the local anaesthetic agent with the controlled release material and then extruding the mixture, eg., under pressure, to thereby obtain biodegradable fibres.
In other embodiments of the invention, the controlled release material comprises an artificial lipid vesicle, or liposome. Liposomes are well known in the art as carriers of bioactive or pharmacologically active substances such as drugs. Liposomes as described herein will vary in size. Preferably, the liposomes have a diameter between 100nm and 10n or greater. A wide variety of lipid materials may be used to form the liposomes including natural lecithins, eg., those derived from egg and soy bean, and synthetic lecithins, the proviso being that it is preferred that the lipids are nonimmunogenic and bio-degradable. Also, lipid-based materials formed in combination with polymers may be used, such as those described in US 5 188 837, (incorporated by reference herein).
Examples of synthetic lecithins which may be used together with their respective phase transition temperatures, are di-(tetradecanoy)phosphatidylcholine (DTPC) di-(hexadecanoyl)phosphatidylcholine (DHPC) (41°C) and di-(octandecanoyl) phosphatidylcholine (DOPC) (55C). Di-(hexadecanoyl) phosphatidycholine is preferred as the sole or major lecithin, optionally together with a minor proportion of the di-(octadecanoyl) or the di-(tetradecanoyl) compound. Other synthetic lecithins which may be used are unsaturated synthetic lecithins, for example, di-(oleyl)phosphatidyl-choline and di-(linoleyl)phosphatidylcholine. In addition to the main liposome-forming lipid or lipids, which are usually phospholipids, other lipids (eg. 1n a proportion of 40% w/w of the total lipids) may be included, for example, cholesterol or cholesterol stearate, to modify the structure of the liposome membrane, rendering it more fluid or more rigid depending on the nature of the main liposome-forming lipid or lipids.
In other preferred formulations, the lipids containing the local anaesthetic agent are dispersed in a pharmaceutically acceptable aqueous medium. In a further embodiment, a portion of the dose of the local anaesthetic is incorporated into the aqueous medium in immediate release form to form an aqueous pharmaceutical suspension useful for administration at the desired site in the patient to be anaesthetised. This may be accomplished via injection or implantation. Liposomes may be prepared by dissolving an appropriate amount of a phospholipid or mixture or phospholipids together with any
LibC/447323d1speci other desired lipid soluble components cholesterol, cholesterol stearate) flowing in a suitable solvent ethanol) and evaporating to dryness. An aqueous solution of the local anaesthetic, optionally with augmenting agent, may then be added and mixed until a lipid film is dispersed. The resulting suspension will contain liposomes ranging in size, which may then fractionated to remove undesirable sizes, if necessary. This fractionation may be effected by column gel chromatography, centrifugation, ultracentrifugation or by dialysis, as well known in the art.
The above method of preparation of liposomes is representative of a possible procedure only. Those skilled in the art will appreciate that there are many different methods of preparing liposomes, all of which are deemed to be encompassed by the present disclosure. In certain embodiments where the substrate is a microsphere, the microspheres include from about 5wt% to about 95wt% drug and from about 5wt% to about 95wt% polymer. In certain preferred embodiments, the drug is included in the microspheres in an amount from about 20wt% to about 90wt%, more preferably from about to about 80wt%, and more preferably from about 70wt% to about 75wt%, (high-microspheres).
The term "microspheres" are defined for purposes of the present invention as particles comprising local anaesthetic and eg., the aforementioned polymeric materials (used as a controlled release carrier for the drug) which are preferably anywhere from about 20pn to about 200 n, and more preferably from about 45 to about 90 Vn in diameter.
The microspheres are preferably formed in such a size as to be injectable. For purposes of the present invention, the term "microsphere" encompasses "microparticle" and "microcapsule". The polymeric material used in the microspheres of the present invention preferably have a molecular weight from about 5000 to about 200000.
The polymeric material may be prepared by any method known to those skilled in the art. For example, where the polymeric material is comprised of a copolymer of lactic and glycolic acid, this copolymer may be prepared by the procedure set forth in US 4 293 539, hereby incorporated by 25 reference. Basically, therein the copolymers are prepared by condensation of lactic acid and glycolic acid in the presence of a readily removable polymerisation catalyst a strong acid ion-exchange resin such as Dowex HCR-W2-H). The amount of catalyst is not critical to the polymerisation, but typically is form about 0.01 to about 20 parts by weight relative to the total weight of combined lactic acid and glycolic acid. The polymerisation reaction may be conducted without solvents at a temperature from about 100C to about 250"C for about 48 to about 96h, preferably under a reduced •pressure to facilitate removal of water and by-products.
The copolymer is then recovered by filtering the molten reaction mixture to remove substantially all of the catalyst, or by cooling and then dissolving the reaction mixture in an organic solvent such as dichloromethane or acetone and then filtering to remove the catalyst.
35 Polyanhydrides may be prepared in accordance with the methods set forth in US 4 757 128, hereby incorporated by reference. For example, polyanhydrides may be synthesised by melt polycondensation of highly pure dicarboxylic acid monomers converted to the mixed anhydride by reflux in acetic anhydride, isolation and purification of the isolated prepolymers by recrystallisation, and melt polymerisation under low pressure (10mm) with a dry ice/acetone trap at a temperature between 140-250"C. for 10-300 minutes. High molecular weight polyanhydrides are obtained by
LibC/447323d1speci inclusion of a catalyst which increases the rate of anhydride interchain exchange, for example, alkaline earth metal oxides such as CaO, BaO and CaCO3. Polyorthoester polymers may be prepared, eg., as set forth in US 4070 347, hereby incorporated by reference.
Various commercially available poly (lactide-co-glycolide) materials (PLGA) may be used in the preparation of the microspheres of the present invention. For example, poly(d,l-lactic-co-glycolic acid) are commercially available. A preferred commercially available product is a 50:50 poly lactic coglycolic acid having a mole composition of 50% lactide and 50% glycolide. Other suitable commercially available products are 65:35 DL, 75:25 DL, 85:15 DL and poly(d,l-lactic acid) (d,l-PLA). For example, poly(lactide-co-glycolides) are also commercially available from Boehringer Ingelheim (Germany) under its Resomer@ mark, eg., PLGA 50:50 (Resomer RG 502), PLGA 75:25 (Resomer RG 752) and d,l-PLA (Resomer RG 206), and from Birmingham Polymers (Birmingham, Alabama). These copolymers are available in a wide range of molecular weights and ratios of lactic to glycolic acid.
The polymers utilised in the microspheres of the present invention may be prepared, eg., by the condensation of lactic acid and glycolic acid in the presence of a readily removable polymerisation catalyst. Such catalysts include strong acid ion-exchange resins in the form of beads or similarly hard structures which are easily removed by filtration or similar techniques. Further information concerning the preparation of the copolymers of the present invention is readily available to those skilled in the art, and may be ascertained from, eg., US 4 293 539, hereby incorporated by reference.
Pharmaceutically acceptable polyanhydrides which are useful in the present invention have a water-labile anhydride linkage. The rate of drug release can be controlled by the particular polyanhydride polymer utilised and its molecular weight. The polyanhydride polymer may be branched or linear. Examples of polyanhydrides which are useful in the present invention include homopolymers and copolymers of poly(lactic acid) and/or poly(glycolic acid), poly[bis(p-carboxyphenoxy)propane anhydride] (PCPP), poly[bis(p-carboxy)methane anhydride] (PCPM), polyanhydrides of oligomerised unsaturated aliphatic acids, polyanhydride polymers prepared from amino acids which are modified to include an additional carboxylic acid, aromatic polyanhydride compositions, and co-polymers of polyanhydrides with other substances, such as fatty acid terminated polyanhydrides, eg., polyanhydrides polymerised from monomers of dimers and/or trimers of unsaturated fatty acids or unsaturated aliphatic acids.
The biodegradable controlled release microspheres of the present invention may be prepared by any procedure known to those skilled in the art. In certain preferred embodiments, however, the microspheres may be obtained by utilising a solvent extraction technique (reactor process) which involves dissolving the drug and the polymer in an organic solvent such as ethyl acetate. This solution thereby obtained (the dispersed phase) is added to a solution of, eg., polyvinyl alcohol (PVA) in water (the continuous phase) with stirring. The emulsion thereby formed is then added to water in order to extract the solvent and to harden the microspheres. The mixture is then filtered and the microspheres are dried. One appropriate method of drying is, eg., under vacuum at room temperature. The desired particle size fraction is then collected by sieving. The organic solvent utilised is preferably ethyl acetate; however, any pharmaceutically acceptable organic solvent may be utilised, such as acetone,
LibC/447323d1speci ethanol, diethyl ether, methanol, benzyl alcohol, methylene chloride, petroleum ether or others, This procedure is particularly useful for preparing microspheres of bupivacaine base.
Alternatively, the microspheres of bupivacaine base may be prepared by dissolving the drug and polymer in ethyl acetate and thereafter spray drying the solution.
In instances where the microspheres are to incorporate drugs which are very water soluble and insoluble in ethyl acetate, such as bupivacaine MCI, the microspheres may be prepared using a coacervation! phase separation rather than the solvent extraction technique described above. However, the solvent extraction technique can be used with bupivacaine HCI due to its low water solubility at pH7.4 and above. The coacervation/phase separation technique utilised involves dissolving the polymer in ethyl acetate and suspending micronised bupivacaine HCI in the solution. Silicone oil is then added to form the microspheres. This mixture is then added to heptane to harden the microspheres, which are then separated by filtration. The microspheres are dried under a vacuum at room temperature. The desired particle size fraction is then collected by sieving.
Alternatively, microspheres prepared using bupivacaine HCI may be accomplished by suspending the drug in a solution of polymer in ethyl acetate or in methylene chloride and methanol and spray drying.
Alternatively, the bupivacaine HCI may be dissolved in water, and the polymer may be dissolved in ethyl acetate. The water phase then can be added to the organic phase and homogenised to yield a W/O emulsion. The drug being in the water phase would then be surrounded by polymer (oil phase). This is then added to the PVA solution in water with stirring to form a W/O/W emulsion. The solvent would diffuse out, leaving microspheres.
Additional cold water can be added to harden the microspheres. This process may yield more uniform microspheres without requiring micronisation of the drug. Also, as the drug will be surrounded by polymer, the release of the drug may be more uniform and would be diffusion-controlled. 25 The ultimate drug content of the microspheres according to the present invention may be varied substantially, depending upon whether a high load or a low load formulation procedure is utilised. In certain preferred embodiments where the drug is bupivacaine), the drug content of the high-load :microspheres may be from about 40 to about 95%, preferably from about and more preferably from about 70% to about 75% of the total weight of the microsphere, and the drug content of the low-load microspheres may be from about 0.1 to about 40% and from about 5% to about
In one preferred embodiment of the present invention, the drug included in the microspheres is
e a local anaesthetic either of the ester or amide type. Suitable local anaesthetics of the ester type include the benzoic acid esters piperocaine, meprylcaine, isobucaine), the para-aminobenzoic acid esters procaine, tetracaine, butethamine, propoxycaine, chloroprocaine); meta-35 aminobenzoic acid esters metabutethamine, primacaine), paraethoxybenzoic acid esters (eg., parethoxycaine), and their pharmaceutically acceptable salts. The non-esters include, eg., lidocaine, mepivacaine, pyrrocaine, prilocaine, bupivacaine, etidocaine, pharmaceutically acceptable salts. A most preferred local anaesthetic is bupivacaine.
In certain preferred embodiments of the present invention, the microspheres incorporate bupivacaine as the drug in an amount from about 45wt% to about 70wt%, the copolymer being PLGA
LibC/447323d1speci 50:50 of a molecular weight from about 5000 to about 200 000. The microspheres of the present invention preferably provide a sustained action in the localised area to be treated. For example, when the drug included in the microspheres is bupivacaine, it would be desirable that such a formulation could provide localised anaesthesia to the area in question for a period of one day, two days, three days, or longer. The formulations can therefore, of course, be modified in order to obtain such a desired result. The microspheres of the present invention may be utilised as a controlled release formulation preferably by incorporating an effective amount of the same into a pharmaceutically acceptable solution water) or suspension for injection. The final reconstituted product viscosity may be in a range suitable for the route of administration. In certain instances, the final reconstituted product viscosity may be, eg., about 35cps. Administration may be via the subcutaneous or intramuscular route. However, alternative routes are also contemplated, and the formulations may be applied to the localised site in any manner known to those skilled in the art, such that a localised effect is obtained. The micro-spheric formulations of the present invention can be implanted at the site to be treated.
Thereby, the formulations of the present invention, when including a local anaesthetic, may be used in the control of post-operative pain.
The dosage of the controlled release microsphere formulations of the present invention is dependent upon the kind and amount of the drug to be administered, the recipient animal, and the objectives of the treatment. For example, when the drug included in the microspheres of the present invention is bupivacaine, the formulation may include, eg., from about 0.5 to about 2mg/kg body weight. The effective dose of bupivacaine, or an amount of another local anaesthetic sufficient to provide proportional potency, can range from about 1 to 50mg of bupivacaine injected or inserted at each site where the release of a local anaesthetic agent is desired. In certain preferred embodiments, the dose of bupivacaine in the controlled release dosage form of the invention is sufficient to provide a 25 controlled release of about 1 to 4mg per day at the release site for at least 1 to 4 days. Since the formulations of the present invention are controlled release, it is contemplated that formulations may :i include much more than usual immediate release doses, eg., as much as 120mg/kg bupivacaine or more.
The local anaesthetic is incorporated into the polymer or other controlled-release formulation in a percent loading between 0.lwt% and 90wt%, preferably between 5wt% and 75wt%. it is possible to tailor a system to deliver a specified loading and subsequent maintenance dose by manipulating the percent drug incorporated in the polymer and the shape of the matrix or formulation, in addition to the form of local anaesthetic free base versus salt) and the method of production. The amount of drug released per day increases proportionately with the percentage of drug incorporated into the formulation, eg., matrix (for example, from 5 to 10 to In the preferred embodiment, polymer matrices or other formulations drug incorporated from about 70wt% to about 75wt%, are utilised, although it is possible to incorporate substantially more drug, depending on the drug, the method used for making and loading the device, and the polymer.
LibC/447323d1speci The formulation of controlled release substrate comprising local anaesthetic provides, in vitro, from about 10 to about 60% release of local anaesthetic after 24h, from about 20 to about release after 48h and from about 40 to about 100% release after 72h.
In a preferred embodiment, the formulation of controlled release substrate comprising local anaesthetic provides, in vitro, from about 25 to about 40% release of local anaesthetic after 24h, from about 40 to about 50% release after 24h and from about 45 to about 55% release after 72h and 80 to 100% cumulative release 'is provided after about 280h.
The reader is reminded that the above listed, in vitro release parameters are not indicative of the duration of local anaesthesia effects in vivo, but are release parameters that, in one embodiment, lo characterise the formulation according to the invention.
The rate of release of local anaesthetic agent or other drugs incorporated into the formulation will also depend on the solubility properties of the local anaesthetic or drug. The greater the solubility in water, the more rapid the rate of release in tissue, all other parameters being unchanged. For example, those local anaesthetic agents having pH dependent solubility will be released more rapidly at the optimum pH for those compounds. Thus, the formulation may be optimised for the desired local anaesthetic release rate by selecting local anaesthetic agents having a desired water solubility in tissue, eg., at tissue pH. Thus, a local anaesthetic agent that is more soluble at acid p1-I will have a faster release rate in a relatively acidic pH less than about 7.2) tissue. For example, in one embodiment, the formulation will have released, in vitro, at least 70% of a local anaesthetic at 48h at about pH6 and will have released at least 40% of a local anaesthetic at a pH ranging from about 7.4 to about 8, at 48h. Other combinations are pH independent in their release.
Potential applications include any condition for which safe localised anaesthesia is desirable. This includes both nerve blockade for the relief of pain and motor symptoms as well as nerve blockade for other medical purposes. The methods according to the invention can be used to provide 0 25 safe local anaesthesia such as, for example, two to five day intercostal blockade for thoracotomy, or longer term intercostal blockade for thoracic post-therapeutic neuralgia, lumbar sympathetic blockade for reflex sympathetic dystrophy, or three-day ilioinguinal/iliohypogastric blockade for hemia repair. Other potential applications include local anaesthesia having enhanced safety for obstetrical or to. gynaecological procedures. Yet further potential applications include providing localised temporary sympathectomy, eg., blockade of sympathetic or parasympathetic ganglia to treat a variety of autonomic diseases, including circulatory dysfunction or cardiac dysrhythmias with enhanced safety. The formulations may also be used to treat trigeminal neuralgia and other diseases of the cranial nerves as well as to provide temporary nerve blockade to treat localised muscle spasm and treatment of retrobulbar conditions, eg., eye pain. Other uses include intra-operative administration in order to l l 35 reduce pain during and after the operative procedure, especially for plastic surgery procedures where prolonged nerve blockade will enhance the outcome having enhanced safety. These are merely examples, and additional uses for both human and veterinary practice are immediately apparent to the artisan.
LibC/447323d1speci Methods of Administration
In a preferred method of administration a dosage form, eg., microspheres, are administered by injection into a site where local anaesthetic agent is to be released. Microspheres may be injected through a syringe or a trochar. Pellets or slabs may be surgically placed into a site where release of oral anaesthetic agent is desired.
The microspheres may be prepared from PLGA polymers ranging from, for example, PLGA in a ratio of 50:50, 65:35 or 75:25. An optimum composition has been determined to be PLGA 65:35. The microspheres, formulated with, eg., PLGA 65:35 microspheres are administered in a dose ranging from, for example, 2 through 450mg of microspheres 75% loaded with a local anaesthetic such as bupivacaine, per kg of the patient to be treated.
In a preferred embodiment the dose ranges from 50 through 450mg/kg. In a more preferred embodiment the dose ranges from about 10 to about 150mg/kg with PLGA 65:35. Certainly, the artisan will appreciate the fact that the dose ranges mentioned above are based on the potency of bupivacaine, and that exact effective dosages will vary with the particular relative potency and pharmacokinetics of each local anaesthetic and will be able to readily adjust the dose according to the degree of blockade experienced by the patient.
The formulation described herein can also be used to administer local anaesthetic agents that produce modality-specific blockade, as reported by Schneider, et al., Anesthesiology, 74:270-281(1991), or that possess physical-chemical attributes that make them more useful for sustained release then for single injection blockade, as reported by Masters, et al., Soc Neurosci. Abstr., 18:200 (1992), the teachings of which are incorporated herein.
Safety Enhancement
It has been found that the methods according to the invention utilising safe, regulated release local anaesthetic preparations provides at least an order of magnitude reduction in the risk of toxic 25 and/or untoward effects relative to conventional methods for providing local anaesthesia.
Studies were conducted with a microsphere preparation composed of poly (lactide-co-glycolide) S: materials (PLGA) in the ratio of 65:35 with a size range of 25-125n, loaded with from about 70% to about 75% with the local anaesthetic bupivacaine (referred to hereinafter as long acting bupivacaine or Doses of drug refer to bupivacaine dose; thus, total mass administered is 1.33 times the indicated dose of LAB. Methods for inducing local anaesthesia with these materials have been evaluated in test animals, including rats, dogs and sheep.
Dose-duration studies in these species, with administration of bupivacaine, indicates 30 that duration of local anaesthesia is a function of the amount of bupivacaine injected around a nerve, rather than the amount injected per unit of body weight. It has been determined that the optimal dose of bupivacaine ranges from about 1 to about 100mg per nerve and more preferably from about 25 to about 75mg per nerve or about 40 to 50mg per nerve and most preferably at about 50mg per nerve. Measurements conducted on both sensory and motor nerve blockade provided similar results.
In tests with formulations according to the present invention, using long acting bupivacaine formulations, the data indicates that even at doses 10-fold higher than those required to achieve three to five days of anaesthesia, plasma bupivacaine doses not exceed 200 to 650ng/mL.
LibC/447323d1speci This results in an exceptional safety margin since toxicity to bupivacaine is associated with plasma concentrations in excess of 1600ng/mL. In rats, local injection of 25mg/kg (8mg/nerve) of commercial aqueous bupivacaine MCI results in the deaths of about 10% of the animals. Using the LAB preparation, 150mg/kg (50mg/nerve) resulted in three to five days of local anaesthesia and even 600mg/kg (200mg/nerve) resulted in only transient reduced activity in the rats. In dogs, subcutaneous doses of 300mg/kg resulted in plasma bupivacaine concentrations in the range of 400 to 650ng/mL for several days, without signs of toxicity. Further, simulated accidental direct injection of LAB intravenously resulted in no overt toxicity or microscopic pathology, even at extraordinarily high doses. This observation confirms that LAB can provide both a prolonged duration of local anaesthesia, as required, but a vastly improved therapeutic index for bupivacaine compared to conventional bupivacaine preparations, eg., bupivacaine HLC.
Examples
Examples 1-3 (Solvent Extraction Process
In Examples 1-3, bupivacaine microspheres are prepared by dissolving the bupivacaine base and the polymer in ethyl acetate. The polymer is 50:50 poly lactic co-glycolic acid which has a mole percent composition of 50% lactide and 50% glycolide. This dispersed phase is then added to a solution of polyvinyl alcohol (PVA) in water (the continuous phase) with stirring. The resulting emulsion is monitored for droplet size, which is in tum controlled by the rate of stirring. The emulsion is then added to water to extract the solvent and to harden the microspheres. The mixture is then filtered and the microspheres are dried under vacuum at room temperature. The desired particle size fraction is then collected by sieving.
Each of Examples 1-3 are prepared such that the microspheres have a relatively high drug content. In Example 1, the theoretical drug content is about 60%, and the size of the microspheres range from about 45 to about 90pm. In Example 2, the theoretical drug content is about 61%, and the range in the size of the microspheres is from about 45 to about 63pn. in Example 3, the theoretical drug content is about 65%, and the range in particle size of the microspheres is from about 45 to about 63pn.
The microspheres of Examples 1-3 are then suspended in a suitable media for injection, in this case water. Thereafter, the microspheres are subjected to in-vitro dissolution testing. An automated dissolution test method is utilised using the USP/NF Paddle Method II. The dissolution medium is 900mL of Tris buffer with 0.05% sodium dodecyl sulfate at pH7.4 at 370C with a stirring speed of about 50rpm. The surfactant is added in order to prevent the microspheres from floating on the surface of the dissolution medium. The dissolution data for the microspheres of Examples 1-3 are presented in Fig. 1, and further information concerning these formulations is presented in Table I below.
Table 1
LibC/447323d1speci From the results set forth in Fig. 1 and Table 1, no correlation between drug content 25 and release rate can be readily made,
It was expected that the formulation of Example 3 would release drug faster than that of Example 1 because of a higher drug content. However, the in-vitro release for Example 3 was slower than expected. It is hypothesised that this is due to the glass transition temperature of the polymer being lowered (below about 37*C) by the high drug content, This situation may or may not be translated into in-vivo results.
Examples 4-9 (Spray-Dried)
In Examples 4-9, the bupivacaine base and the polymer utilised in Examples 1-3 are once again dissolved in ethyl acetate, but this time the microspheres are obtained by spray-drying the solution. Example 4 utilises a relatively high drug content, whereas Example 5 utilises a relatively low drug content. In Examples 7-9, microspheres having a substantially similar drug content to Examples are prepared using the solvent extraction technique utilised in Examples 1-3. Details of the formulations are presented in Table 2 below.
Table 2
With regard to Example 9, the actual percentage of bupivacaine base in the microspheres is 51%, the molecular weight of the 50:50 dl-PLGA polymer is 18000, the microspheres were about 631n, and in-vitro dissolution conducted as in Examples 1-.3 showed that 61% of the bupivacaine was released in 22h.
20 The microspheres of Examples 6 and 9 are suspended in a suitable injection medium (eg., water) and then subjected to in-vitro dissolution testing via the procedures set forth in Examples 1-3. The in-vitro dissolution results are determined for 22h, and are graphically depicted in Fig. 2.
In Fig. 3, the in-vitro dissolutions of Examples 4-5 and 7-8 are determined as per the Examples S above, and compared to the dissolution of the bupivacaine free base and the bupivacaine hydrochloride salt forms. As can be seen from the graph of Fig. 3, when compared to pure bupivacaine base, each of Examples 4-5 and 7-8 showed a distinct retarding effect in their dissolution profile. Furthermore, all four examples of the invention displayed a small initial burst of drug release which was more pronounced in the microspheres prepared by the spray-dried process as compared to the examples prepared by the solvent extraction process.
Scanning electron micrographs of the microspheres for the formulations prepared by the Ssolvent extraction and by the spray-dried technique are then compared. The spray-dried process yields microspheres which are smaller than with the solvent extraction process.
Example 10 in vitro Release Characteristics of Bupivacaine from Microspheres Studies were carried out in vitro to monitor the rate of release of bupivacaine from the 65:35 PLGA, 75:25 PLGA and PLA 100 microspheres loaded with bupivacaine from about 70% to about
LibC/447323d1speci Release experiments were carried out in vitro in stirred, buffered physiological saline, the buffer being changed at the points indicated on the accompanying graph (Figure The amount of bupivacaine in each of the supernatants was quantitated spectrophotometrically. In some experiments, release of tritiated bupivacaine was quantitated.
Generally, the PLA 100 microspheres released the bupivacaine most rapidly, with about release attained in less than 1 day. PLGA 75:25 and 65:25 microspheres reached about 80% release after about 10 days, as illustrated by Figure 4.
Example 11 Pharmacodynamics of Anaesthesia in Response to Lab Methods:
Rat hot plate assay
Rats were anaesthetised with halothane during drug administration. Microsphere preparations were injected in 0.6mL using an 18 gauge needle, proximal to the sciatic nerve, using anatomic landmarks. Data are presented as latency. Latency refers to the amount of time an animal voluntarily leaves its paw on the hot plate (maintained at 56°C), about 2s in a normal animal. In animals experiencing local anaesthesia, paws are removed from the hot plate after 12s by the experimenter to avoid tissue damage.
Results
Dose-response studies were performed using 50-600mg/kg body weight bupivacaine. It was determined that doses as high as 600mg/kg can be administered, with transient decreased activity as the only observable side effect at the highest dose.
Example 12: Preparation of Microspheres with Bupivacaine at >70wt% Loading Materials
Microspheres with bupivacaine free base loaded at greater than 70wt%, were prepared by a process using the materials provided by Table 3, below, in the indicated proportions.
Table 3
Materials For Preparation of High Load Bupivacaine Microspheres
Removed during processing.
Equipment
The stock solutions for the preparation of the microspheres were prepared with standard laboratory equipment, eg., beakers and mixers. The final mixing of the organic phase and aqueous phase solutions and quenching, was conducted in an apparatus having a temperature regulated circulating water bath, and at least two reactor vessels for holding the organic and aqueous phase solutions, of 2 and 3L, respectively, and a quench tank. The reactor vessels (or simply "reactors") was each equipped with a mixing propeller. The apparatus also included a static mixer and gear pump for each reactor.
LibC/447323d1speci Process
The high load bupivacaine containing microspheres were prepared as follows.
A. Preparation of 65:35 organic phase polymer solution.
Ethyl acetate (937.5g) was added to a 2L beaker followed by the addition of 42.00g of 65:35 PLGA with moderate mixing. The container was covered and moderate mixing continued until a clear solution was formed.
B. Preparation of Polyvinyl alcoholrrris buffer aqueous solution.
Polyvinyl alcohol (PVA; 600g) was added to a 4L beaker and then diluted with 2201g purified water followed by stirring. Thereafter 6.63g Tris HCI and 13.08g Tris base were added with stirring until the solution was clear, then the stirring was halted and the beaker covered. The buffer solution had a measured pH of about 8.47.
C. Preparation of quench media.
A quench tank was filled with 69.54kg of purified water. The quench tank propeller mixer was run at a moderate speed and 154.7g Tris MCI and 305.2g Tris base were added to the quench tank with stirring, until a clear solution was formed. The quench media had a measured pH of about 8.50.
D. Completing preparation of organic phase by adding bupivacaine.
The weight of the organic phase polymer solution prepared at step A above was adjusted to 975.0g as required and the polymer solution was transferred to a 2L temperature regulated reactor and 108g of bupivacaine base was added to the organic phase polymer solution with stirring by a built in propeller.
E. Completing preparation of aqueous phase by adding ethyl acetate.
Ethyl acetate, 1 80.0g was added to the polyvinyl alcohol Tris buffer of step B, above, with about 2 minutes of moderate stirring by a built in propeller. The stirred aqueous phase solution was transferred to a 3L temperature regulated reactor.
F. Mixing and quenching of the organic and aqueous phases
The propeller in the quench mixing tank was placed at an angled position about 8cm from the bottom of the tank and activated to about 800cpm. The outlet tube of the static mixer was positioned below the propeller mixing blades of the quench tank, the propeller mixer was turned off and the pumping of the aqueous phase through the static mixer was commenced. The flow of the organic phase through the static mixer was established through the static mixer, which took about 10.1 minutes to drain the organic phase reactor, at which time the organic phase pump was turned off The aqueous phase pumping continued through the static mixer for rinsing until all of the aqueous phase was exhausted, at which time the aqueous phase pump was shut down. The quench phases was then stirred for about one hour after the organic phase reactor is emptied.
G. Microsphere Collection, Sieving and drying.
A peristaltic pump was used to pump suspended microspheres through stacked sieves, two 25 pm sieves and two of 1351nm, Each sieve collection was then rinsed with about 2L of purified water. About 231.5g of wet microspheres were collected from the 25pm sieves and about 92g of wet microspheres were collected from the 1251pm sieves. After drying at room temperature overnight and removal from the sieves, the yield was about 110g of microspheres from the 25 .m sieves and about 16.7g of microspheres from the 125pn sieves. The microspheres were then further treated by drying at about 18.5-18.8 0C, in a vacuum oven, followed by a final screening through a 1251m sieve.
LibC/447323d1speci H. Bupivacaine content confirmed.
The microspheres so produced were assayed for bupivacaine content by standard methods, which was determined for the batch produced as described above as 72.00% bupivacaine and 28.99% 65:3 5 high iv PLGA or 50.00mg bupivacaine per dose and 19.44mg/dose of the PLGA.
I. Multiple batches were pooled.
Multiple batches of microspheres were prepared as described above and the so obtained microspheres pooled to provide the microspheres for the safety determinations described herein.
Example 13 Single Dose Toxicity in Rats
Methods
Sprague-Dawley rats from Charles River, 6-8 weeks of age (body weight about 15-200g for females and about 200-290g for males) were used for these studies.
Male and female rats were dosed intramuscularly in the hind limb with bupivacaine base (the form used in the microspheres), aqueous bupivacaine HCI, or LAB. The animals were examined for pharmacotoxic signs (including tremors and convulsions, and death).
The results of the intramuscular study are summarised in Table 4, below. These data indicate that LAB has an excellent safety margin versus bupivacaine free base, for example, after intramuscular dosing, the lowest lethal dose of bupivacaine hydrochloride was 10.6mg/kg, whereas no toxic effects were found in rats given up to 400mg/kg LAB. Temporary paralysis of the hindlimb was observed in animals dosed with bupivacaine in microspheres (local motor anaesthesia). More transient paralysis was observed after administration of aqueous bupivacaine hydrochloride. This is a reflection of the expected pharmacology of bupivacaine.
Table 4
Summary of acute lethality studies in rats given intramuscular doses of bupivacaine HCI, bupivacaine free base or bupivacaine containing microspheres("LAB").
:00. o *.o0
All deaths occurred 10-30 minutes post-dosing
*1/4 with seizures
LAB is long acting bupivacaine (microspheres).
Therefore, the data of Table 4 confirm that the methods and formulations according to the invention provide a safer local anaesthesia than has heretofore been available.
Conclusion
The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the invention in addition to those described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are intended to fall within the scope of the claims. Various publications are cited herein, the disclosures of which are incorporated by reference in their entireties.
LibC/447323d1speci