HK1097460B - Process for producing injectable gabapentin compositions - Google Patents

Description

Method for producing gabapentin composition for injection

RELATED APPLICATIONS

This application claims provisional application serial No. 60/513682 entitled "injectable gabapentin composition" filed on 23/10/2003, provisional application serial No. 60/513681 entitled "intrathecal administration of gabapentin for the treatment of pain and epilepsy" filed on 23/10/2003, and priority to U.S. patent application serial No. 10/808,113. The contents of all of the above applications are incorporated herein by reference.

Technical Field

The present application relates to injectable compositions and kits comprising gabapentin and to methods for their production.

Background

Gabapentin is an agent that mimics the action of GABA (gamma-aminobutyric acid), but gabapentin does not appear to bind GABA receptors (e.g., GABA)_AAnd GABA_BReceptor) does not affect GABA uptake. Gabapentin was found to interact with α -2- δ (α) of voltage-gated calcium channels₂δ) subunit interactions. Many of the pharmacological effects of gabapentin are due to its interaction with voltage-gated calcium channels. Gabapentin is thought to reduce calcium ion influx into neurons, reducing neuronal excitability. Inhibition of presynaptic calcium influx may prevent neurotransmitter release. Thus, like GABA, gabapentin can alleviate overactivity of the neural circuit.

Solid formulations of gabapentin, such as NEURONTIN, are currently available for oral administration. Oral gabapentin was originally used to treat epilepsy, although not identified as being also used to treat neuropathic pain and has recently been approved by the FDA for the treatment of one type of neuropathic pain, post-herpetic neuralgia. Some gabapentin may enter the CNS when administered orally, as gabapentin can be transported across the intestinal and blood-brain barriers. Gabapentin is thought to be transported across the blood-brain barrier by active and saturable L-amino acid transporters. Thus, the amount of gabapentin reaching the site of CNS effects is limited. Because the transporter is saturable, even if the concentration of gabapentin in the blood is elevated, its amount across the blood-brain barrier does not change.

In preclinical animal experiments, gabapentin solutions were extemporaneously prepared for direct administration to the CNS. In some studies, a single bolus or multiple boluses of the gabapentin solution were administered intrathecally. However, the administration of gabapentin solutions to the CNS poses a number of problems, including the threat of serious infection. While these problems are not of great importance in preclinical animal testing, they are of paramount importance when administered to humans.

Therefore, the sterility of gabapentin-containing solutions, which are to be administered to the CNS, cannot be treated with little effort. Typically, the solution is sterilized by heating or filtration. In the case of solutions containing gabapentin, sterilization processes involving heat are generally undesirable. This is because heat will cause a decrease in the stability of gabapentin and increase the production of gabapentin lactam having the chemical structure of formula (I):

according to U.S. Pat. No. 6,054,482, "lactams exhibit certain toxicity and must therefore be avoided as much as possible, for example, the toxicity of gabapentin (LD)₅₀Mouse) is greater than 8000mg/kg, while the corresponding lactam (VI) has a toxicity of 300 mg/kg. "column 4, lines 50-53. Since sterilization processes involving heat can increase the level of gabapentin lactam, it is not recommended to heat the solution prior to administration to the CNS of a patient.

Summary of The Invention

One embodiment of the present invention provides a method for preparing a pharmaceutical injectable composition comprising gabapentin. The method comprises heating the injectable composition. Surprisingly, the inventors have found that heating an injectable composition containing gabapentin while introducing into the CNS does not result in excessive toxicity.

Will addThe hot gabapentin-containing injectable composition has several advantages as part of the sterilization process. For example, the use of heat as a means of terminal sterilization allows for sterilization of large quantities of gabapentin-containing compositions in an efficient manner. In addition, heat treatment after filter sterilization can further ensure that the gabapentin-containing composition is sterile to the desired F₀Administered to the CNS or other areas of the patient. These and other advantages of the invention will be apparent from a reading of this specification.

Detailed Description

The following description illustrates various embodiments of the invention. It is to be understood that other embodiments of the invention are contemplated and may be made without departing from the scope or spirit of the present invention. The following description is, therefore, not to be taken in a limiting sense.

Unless defined otherwise, all scientific and technical terms used herein have the same meaning as commonly understood in the art. The definitions provided herein facilitate understanding of certain terms used frequently herein and are not intended to limit the scope of the present invention.

In the context of the present invention, the terms "treat", "treatment", and the like, when referring to a disease, shall include methods of alleviating, slowing the progression of, preventing, alleviating, or curing the target disease.

As used herein, a heated injectable composition refers to a composition that has been heated at some point. It is to be understood that the heated injectable composition may be at substantially room temperature, or any other desired temperature, prior to injection into a subject.

As used herein, the term "injectable pharmaceutical composition" refers to a composition that can be infused or injected into a subject, the composition containing a pharmaceutically active agent and sterilized to F₀Or equivalent forms, suitable for administration to a human patient by injection or infusion.

Embodiments of the present invention provide injectable compositions comprising gabapentin. The injectable composition containing gabapentin prepared according to the embodiment of the present invention can be used for any purpose requiring the study and use of gabapentin. For example, injectable compositions containing gabapentin can be used in studies to determine or elucidate (a) the effects of gabapentin on molecules, cells, tissues, organs, organisms, or combinations thereof; (b) the mechanism of action of gabapentin, (c) the nature of gabapentin, a solution containing gabapentin, or a combination thereof, and (d) and the like. Injectable compositions containing gabapentin may also be used as a therapy for the treatment of diseases or conditions responsive to gabapentin such as epilepsy, pain, tinnitus, drug addiction, bipolar disorder, osteoarthritis, migraine and anxiety disorders including social phobia.

Composition for injection

One embodiment of the present invention provides an injectable composition comprising gabapentin. As used herein, gabapentin refers to 1- (aminomethyl) cyclohexaneacetic acid and pharmaceutically acceptable salts, solvates, hydrates and polymorphs thereof. 1- (aminomethyl) cyclohexaneacetic acid is of the formula C₉H₁₇NO₂Gamma-aminobutyric acid (GABA) analogs having a molecular weight of 171.24. 1- (aminomethyl) cyclohexaneacetic acid is readily soluble in water and in aqueous alkaline and acidic solutions. 1- (aminomethyl) cyclohexaneacetic acid has the following structure:

gabapentin is available from a variety of commercial sources, such as Shanghai Zhongxi international trading co., Shanghai, China; hikal Limited, Bangalore, Karnaraka, India; eregiene s.p.a., San Paolo d' argon (bg), Italy; MediChem, SA, Sant Joan Despi (Barcelona), Spain; ranbaxy Laboratories, New Delhi, India; procos s.p.a., Cameri, Italy; zambon Group, Milan, Italy; hangzhu Chiral Medicine Chemicals Co., Hangzhu, China; InterChemCorporation USA, Paramus, NJ; SST Corporation, Clifton, NJ; tevapharmaceuticals USA, North metals, Pa; plantax USA, hakenpack, NJ; and Sigma-Aldrich, st. Alternatively, gabapentin may be synthesized and/or prepared according to methods known in the art.

Injectable compositions include solutions, suspensions, dispersions, and the like. Injectable solutions, suspensions or dispersions can be formulated according to the known art using suitable dispersing, wetting and suspending agents, for example, sterile oils, including synthetic mono-or diglycerides, fatty acids and oleic acid (see, for example, Remington's Pharmaceutical Sciences, Chapter 43, 14 th edition, Mack Publishing Co., Easton, Pa.).

Injectable compositions containing gabapentin can be prepared in water, saline, isotonic saline, phosphate buffered saline, citrate buffered saline, and the like, optionally mixed with a non-toxic surfactant. Dispersions can also be prepared in glycerol, liquid polyethylene, ethylene glycol, DNA, vegetable oils, triacetin, and the like, and mixtures thereof. Under ordinary conditions of storage and use, these preparations may contain a preservative to prevent the growth of microorganisms. Pharmaceutical dosage forms suitable for injection or infusion include sterile aqueous solutions, suspensions or dispersions, or sterile powders containing the active ingredient which are suitable for the extemporaneous preparation of sterile injectable or infusible solutions or dispersions. Preferably, the final dosage form is a sterile liquid and is stable under the conditions of manufacture and storage. The liquid carrier or vehicle of the solution, suspension or dispersion can be a diluent or solvent or liquid dispersion medium, for example, water, ethanol, polyol such as glycerol, propylene glycol, or liquid polyethylene glycol, and the like, vegetable oils, nontoxic glyceryl esters, and suitable mixtures thereof. Proper fluidity of a solution, suspension or dispersion can be maintained, for example, by the formation of liposomes, by the maintenance of the required particle size in the case of dispersions, or by the use of non-toxic surfactants. Prevention of the action of microorganisms is achieved by various antibacterial and antifungal agents, such as parabens, chlorobutanol, phenol, sorbic acid, thimerosal, and the like. In many cases, it is desirable to include isotonic agents, such as sugars, buffers, or sodium chloride. Delayed absorption of the injectable compositions is facilitated by the incorporation into the compositions of agents which delay absorption, such as aluminum monostearate hydrogel and gelatin. Solubility enhancing adjuvants such as cyclodextrins may be added.

In one embodiment, the injectable composition comprising gabapentin is an injectable composition comprising an aqueous solvent. The solvent may be water or brine. The saline may be, for example, 0.9% (w/v) sodium chloride or a solution of sodium chloride added just enough to make the final injectable composition isotonic. The saline may be sterile saline.

According to various embodiments of the present invention, any concentration of gabapentin may be present in the injectable composition. For example, gabapentin may be present in a solution, suspension or dispersion in a concentration of about 0.1 to 100 mg/mL. In one embodiment, gabapentin is present in a solution, suspension or dispersion in a concentration of about 10 to about 90 mg/mL. In one embodiment, gabapentin is present in a solution, suspension or dispersion in a concentration of about 20 to about 80 mg/mL. In one embodiment, gabapentin is present in a solution, suspension or dispersion in a concentration of about 30 to about 100 mg/mL. In one embodiment, gabapentin is present in a solution, suspension or dispersion at a concentration of about 80 mg/mL. In one embodiment, the injectable composition comprises about 10-50mg/ml gabapentin. For example, the composition may comprise from about 20 to about 40mg/ml, or about 30mg/ml of gabapentin. According to an embodiment of the present invention, a composition for injection containing gabapentin comprises gabapentin in an amount effective to treat a disease responsive to gabapentin. In one embodiment, the amount of gabapentin when administered intrathecally is effective to treat a condition responsive to gabapentin.

In one embodiment of the invention, the injectable composition containing gabapentin has a pH of about 4 to about 9, about 5 to about 7, about 5.5 to about 6.5, or about 6. The pH of the injectable gabapentin composition can be adjusted with a pharmaceutically acceptable acid, base, buffer, or combination thereof. In one embodiment, the pH is adjusted with hydrochloric acid or sodium hydroxide. The hydrochloric acid or sodium hydroxide may be in any suitable form, for example a 1N solution.

In one embodiment, the present invention provides an injectable composition comprising gabapentin, the composition being substantially isotonic with a physiological solution of a subject. For example, the solution for injection may be isotonic with the blood or cerebrospinal fluid of the subject. Cerebrospinal fluid permeability is typically about 305 mOsm. Accordingly, embodiments of the present invention provide injectable gabapentin compositions having an osmolarity of about 290-320 mOsm. Where the osmolarity of the injectable composition containing gabapentin is less than about 290-320mOsm, the osmolarity may be increased by the addition of an osmolarity enhancer such as sodium chloride. As used herein, "permeability enhancer" refers to a compound or composition that increases the permeability of a composition. However, gabapentin compositions often fail to achieve this approximately 290-320mOsm osmolarity. For example, gabapentin dissolved in water at a concentration of 80mg/ml has an osmolarity of about 500 mOsm. When the concentration of gabapentin in the injectable composition is such that the composition is hypertonic relative to a physiological solution of the subject, it is preferred that little or no permeation enhancer is added to the composition. However, it will be appreciated that one or more additional compounds need to be added to the composition, even though the addition of such additional compounds will further increase the permeability of the injectable gabapentin solution. For example, additional therapeutic agents, stabilizers, preservatives, solubilizers, buffers, etc., may be added to the composition, even if permeability is to be increased.

In one embodiment of the invention, the injectable gabapentin composition is substantially free of preservatives, substantially free of buffers, or substantially free of preservatives and buffers.

Sterile injectable compositions containing gabapentin are prepared by mixing the required amount of gabapentin in a suitable diluent or solvent with the various other ingredients enumerated above, as required, followed by sterilization. Any sterilization method may be used. For example, the sterilization process can be accomplished by heating, filtration, aseptic techniques, and the like, or combinations thereof. The heating for sterilization may be heating for terminal sterilization, or may be a heat treatment in connection with filtration and/or aseptic techniques to achieve the desired level of sterilization. In one embodiment, heating may be achieved by autoclaving. As used herein, "autoclave" and similar forms refer to one type of heating. Autoclaving is generally carried out at 121.1 ℃ and 15 psig. In some cases, it is desirable to obtain sterile powders for the preparation of sterile injectable solutions. Such sterile powders may be prepared by vacuum drying and freeze-drying techniques to give a powder which has been sterile-filtered to remove the active ingredient and any other desired ingredients present in the solution.

Heating as part of or to effect sterilization

In one embodiment of the invention, an injectable composition containing gabapentin is heated. Heating may be used to sterilize the injectable composition or may be used to ensure sterility of the aseptically prepared injectable composition. Because elevated temperatures can lead to an increase in the conversion of gabapentin to its corresponding lactam (lactams are generally considered more toxic than gabapentin), it is desirable to avoid elevated temperatures when preparing compositions containing gabapentin. Surprisingly, gabapentin-containing compositions can be heat treated or autoclaved to provide suitable sterile injectable gabapentin compositions. The heating can be carried out at any combination of temperature and time, whether by autoclaving or not, to sterilize the gabapentin-containing composition or to ensure sterility of the aseptically prepared composition. Heating alone is sufficient to sterilize the injectable composition. Alternatively, the heat treatment may be combined with another form of sterilization and/or aseptic technique. For example, the heat treatment may be after filtration. The gabapentin composition for injection can be filtered through a filter that can improve the sterility of the composition. For example, an injectable composition containing gabapentin can be filtered through a filter having a pore size of about 0.2 μm or about 0.22 μm. By way of non-limiting example, the composition can be subjected to heat of greater than or equal to about 105 ℃. In another embodiment, the composition can be subjected to heat at a temperature of greater than or equal to about 105 ℃ for greater than or equal to about 2 minutes. In another embodiment, the injectable composition containing gabapentin may be subjected to heat at a temperature of greater than or equal to about 105 ℃ and 140 ℃ for a time period of greater than or equal to about 2 to 60 minutes, at about 121 ℃ for about 24 minutes, at about 130 ℃ for about 4 minutes, and at about 121 ℃ for about 6 to 8 minutes. In one embodiment, the heating is performed at a temperature of about 121 ℃. It will be appreciated that the higher the temperature, the longer the duration of heat application, and the increased likelihood of gabapentin lactam formation. To prevent excessive lactam formation, the time and temperature of heat application can be adjusted to a combination that reduces lactam formation, yet continue to provide sterile injectable compositions containing gabapentin. To achieve a suitable level of sterilization, heat may be applied in addition to filtration and/or aseptic techniques.

In various embodiments of the present invention, the heated injectable composition containing gabapentin further comprises less than or equal to about 10% gabapentin lactam (formula I), less than or equal to about 5% gabapentin lactam, less than or equal to about 3% gabapentin lactam, less than or equal to about 2% gabapentin lactam, or less than or equal to about 1% gabapentin lactam. The heated injectable composition containing gabapentin may further comprise about 0.5% to about 10% gabapentin lactam, about 0.5% to about 5% gabapentin lactam, about 0.5% to about 3% gabapentin lactam, about 0.5% to about 2% gabapentin lactam, or about 0.5% to about 1% gabapentin lactam. The above lactam levels are suitable for injection into the CNS of a subject and are therefore suitable for use in pharmaceutical compositions. It is understood that gabapentin lactam and other degradation products may be formed during heating. Additional gabapentin may be added prior to heating the composition to compensate for degradation. For example, if an injectable composition containing 80mg/ml gabapentin is desired, and if it is known that about 3% of the gabapentin degrades during heating, then 80mg/ml plus an additional 3% of gabapentin may be present in the injectable composition prior to heating.

In various embodiments of the invention, F is about 1 or greater, about 2 or greater, about 3 or greater, about 4 or greater, about 5 or greater, about 6 or greater, about 7 or greater, about 8 or greater, about 9 or greater, about 10 or greater, about 12 or greater, about 18 or greater, about 24 or greater₀Next, the injection composition containing gabapentin is heated. F₀Is a measure of the efficiency of a particular heat sterilization process, using the minute time at 121 ℃ as a reference. For example, a heat sterilization process in which organisms are destroyed at 121 ℃ for 8 minutes to the same extent has F₀Is 8. In other words, F₀Is the equivalent time of transfer to the container for sterilization purposes at 121 ℃. F₀The transformation of (A) is well within the capabilities of those skilled in the art and can be performed as described in Microbiology and Engineering of Sterilization Processes (Microbiology and Engineering of sterility Processes), 1990 version 7, Irving J.Pflog, fractional Drug Association, Inc Technical Monograph 1 Microbiology and Engineering of Sterilization Processes 2000, reissue, the contents of which are incorporated herein by reference.

In one embodiment, the present invention provides a method for preparing an injectable composition comprising gabapentin. The composition may be a pharmaceutically suitable composition. The method comprises preparing an injectable composition comprising gabapentin and heating the composition to sterilize the composition or to ensure sterility of the composition. Injectable compositions having the above properties can be prepared. In one embodiment, gabapentin in solid form, such as a dry powder, is added to a diluent or solvent to form an injectable composition. Other adjuvants may be added. The injectable compositions can be sterilized, for example, by heating, sterile filtration, and the like, or combinations thereof. The sterilized composition may be placed in a container. In one embodiment of the invention, the sterilized composition is placed in a container in an aseptic manner. The container may be any container capable of holding the injectable composition. Preferably the container is compatible with the injectable composition. In one embodiment, the container is a vial, ampoule, or the like. The diaphragm of a vial, ampoule, or the like may be actuated and capped with a flip-top seal. The sterilization composition is terminally heated by heating the container holding the composition.

Administration of drugs

The injectable composition of the present invention, which has been heated, is administered to a subject by any pharmacologically acceptable route. For example, the compositions can be administered intravenously, subcutaneously, intramuscularly, intraarterially, intraarticularly, intrathecally, epidurally, intraparenchymally, intraperitoneally, intracerebroventricularly, e.g., by infusion or injection.

In one embodiment of the invention, the injectable composition containing gabapentin is suitable for intrathecal administration. Intrathecal administration of gabapentin bypasses the saturable L-amino acid active transport system and the blood-brain barrier while reducing concomitant systemic or supraspinal drug levels, provides a means to achieve effective spinal concentrations of gabapentin, and intrathecal administration of any effective amount of gabapentin. For example, gabapentin may be administered intrathecally in a daily dose of about 0.1-200 mg. It will be appreciated that the daily dosage needs can be adjusted to accommodate variability in CSF volume, CSF production rate, and clearance of gabapentin from CSF. One skilled in the art will appreciate that such variability is due in part to, for example, gender and/or age.

The following patent applications are generally related to injectable gabapentin and its uses:

U.S. patent application Ser. No. 10/807,828 entitled "PAIN TREATMENT by intrathecal administration OF gabapentin" (INTRATHECALCABACANTIN FOR TREATMENT OF PAIN), filed 24/3/2004;

U.S. patent application serial No. 10/808,129 entitled "gabapentin composition for injection" (gabapentin compositions) filed 24/3/2004;

U.S. patent application Ser. No. 10/807,827 entitled "treating EPILEPSY by intrathecal administration OF gabapentin" (INTRATHECALCAGABACETIN FOR TREATMENT OF EPILEPSY) filed 24/3/2004; and

U.S. patent application serial No. 10/808,054 entitled "pump system with injectable GABAPENTIN composition" (PUMPS SYSTEM INCLUDING INPULLING IINJECTABLE GABAPENTIN COMPOSITIONS) filed 24/3 in 2004.

All patents, patent applications, technical literature, or other publications cited herein are each individually incorporated by reference. As will be readily appreciated by those of ordinary skill in the art upon reading this specification, at least some of the compositions, devices, and methods described in the patents and publications cited herein may be further improved in light of the present disclosure.

Examples

The following examples are provided to illustrate specific embodiments of the present invention and should not be construed as limiting the scope of the invention.

Example 1: stability of gabapentin compositions for injection by heating

Gabapentin at a concentration of 80mg/ml was dissolved in sterile water for injection USP (batch No. 1), 50mM sodium phosphate (batch No. 2) or 50mM sodium citrate (batch No. 3). The pH of the resulting solution was adjusted to 6.0. + -. 0.2 with 1N NaOH and/or 1N HCl. 4.5ml of the resulting pH adjusted solution was placed in a 3.5ml vial and autoclaved. Autoclaving at 121 ℃ and 15psig for 12 min (F)₀12), 18 minutes (F)₀18), and 24 minutes (F)₀24). HPLC was used to determine gabapentin and gabapentin lactam concentrations for the autoclaved solution. The results are shown in Table 1.

Table 1: degradation of gabapentin compositions for thermal injection

Batch number	F	Gabapentin (% target level).)	% gabapentin lactam (w/v)
				1	12	98.2	1.54

Batch number	F	Gabapentin (% target level).)	% gabapentin lactam (w/v)
				1	18	97.6	2.12
1	24	97.0	2.81
				2	12	97.4	2.80
2	18	96.8	3.84
				2	24	96.0	4.93
3	12	99.1	2.87
				3	18	97.2	3.84
3	24	95.8	5.06

Target level ═ gabapentin concentration/(80 mg/ml) ] x100

Example 2: the heated gabapentin composition for injection is non-toxic

Rats were intrathecally infused with solutions containing various concentrations of gabapentin. The solution was heated prior to administration and no toxic effects were observed with the infused solution.

Materials and methods

Preparing injection solution containing 80mg/ml gabapentin and heating to F₀Sterilized as described in the examples 24. The heat sterilized 80mg/ml gabapentin solution was diluted in sterile water for injection, USP (Abbott laboratories; North Chicago, Ill.) to prepare solutions of gabapentin concentrations of 1.67, 4.17, and 37.5mg/ml, as shown in Table 2.

Table 2: dilution of gabapentin solution

Group of	Desired concentration (mg/ml)	Volume (ml) of gabapentin	Volume (ml) of vehicle
				1 (control)	0	0	40.0
2 (Low)	1.67	0.84	39.16
				3 (middle)	4.17	2.09	37.91
4 (high)	80.0	40.0	0
				5 (middle-high)	37.5	18.75	21.25

Group of	Desired concentration (mg/ml)	Volume (ml) of gabapentin	Volume (ml) of vehicle
				6 (control)	0	0	40.0

Form a volume of 40ml of the required gabapentin (80mg/ml) and vehicle (sterile water for injection, USP).

For groups 1 and 6, osmotic micropump(s) ((Form 2ML4) was filled with about 2ML of sterile water and about 2ML of the appropriate test formulation for groups 2-5. All formulations were filtered through a 0.22 μm filter before injection into the osmotic micro-pump.

Male and female Crl were designed according to the study shown in table 3:(SD) IGS BR rat groups. Animals were obtained from Charles River Laboratories; raleigh, North Carolina. The supplier intubates the animal in the intrathecal cavity below the lumbar spine. The cannula consists of a 1.3cm PE-10 tube connected to a 7cm piece of polyurethane tubing (0.025 ID. times.0.040 OD) and has a total dead volume of about 23.5 □ l. On day 1 (gender-based crossover), animals were anesthetized and a pre-filled osmotic pump/animal sterile subcutaneous inserted into the back of the animal. The cannula is filled with sterile water or a suitable test agent and the pump is connected to an intrathecal catheter. Animals were dosed at a dose volume of about 60.96 □ l/day, 24 hours/day, by intrathecal infusion starting on day 1 until necropsy on day 29 using an osmotic micro-pump. At the start of administration, the animals were 8-9 weeks old and their weights were 264-340g (male) and 191-264g (female).

Table 3: experimental design and animal assignment

Toxicity was assessed according to mortality, clinical observations, ophthalmic examinations, body weight, food consumption, clinical pathology and anatomical pathology. Ophthalmic examinations were performed before starting treatment and between cycle 4. Indirect ophthalmoscopy procedures are performed, including, but not limited to, gross examination of the ocular appendages and anterior structures (e.g., cornea, anterior chamber, lens) and detailed examination of the fundus. Body weight was measured before, on day 1, and weekly after treatment. Food consumption was measured weekly. Sacrificed as planned and samples taken for hematology, coagulation and clinical chemistry. Possibly, collected from animals sacrificed at unintended intervals. Tissues were removed from groups 1 and 4 and from animals sacrificed at each unplanned interval. Spinal cords were collected from each animal in groups 2, 3 and 5. The tissue and spinal cord were treated and examined microscopically. Animals from groups 2, 3 and 5 were treated and examined microscopically for macroscopic lesions. Spinal cord sections from each animal of groups 1 and 4 were embedded in paraffin, sectioned, stained with lucokoux blue, and examined microscopically. Spinal cord immunohistochemistry sections from each animal of groups 1 and 4 in paraffin were sectioned and stained with anti-collagen fibrillar proteins (Dako; Carpinteria, California); from Vector Laboratories; rabbit IgG from Burlingame, California was used as a negative control and examined.

The following hematological tests were performed: red blood cell (erythrocyte) count, hemoglobin, hematocrit, mean volume of red blood cells, mean corpuscular hemoglobin concentration, platelet count, white blood cell (leukocyte) count, and differentiated blood cell count. The following clotting tests were performed: prothrombin time and activated partial thromboplastin time. Clinical chemistry data were obtained for the following aspects: glucose, urea nitrogen, creatinine, total protein, albumin, globulin, albumin/globulin ratio, cholesterol, triglycerides, total bilirubin, alanine aminotransferase, alkaline phosphatase, gamma glutamyltransferase, aspartate aminotransferase, calcium, inorganic phosphorus, sodium, potassium, and chloride. At sacrifice the following tissues were collected and weighed: adrenal gland, brain, epididymis, heart, kidney, liver, lung, ovary, pituitary, prostate, salivary gland (of the mandible), seminal vesicle, spleen, testis, thymus, thyroid with parathyroid and uterus. The damaged organs such as adrenal gland, epididymis, kidney, ovary, etc. are weighed together. Organ-body weight percent and organ-brain percent were calculated. The following tissues were stored in 10% neutral buffered formalin: adrenal gland, brain, cecum, colon, duodenum, epididymis, esophagus, eye, femur with bone marrow (distal articular surface), hadean gland, heart, ileum, infusion and intubation sites and pumps, jejunum, kidney, lacrimal gland (extraorbital), injury, liver, lung with bronchial stem, lymph node (mesenteric), breast (female), optic nerve, ovary, pancreas, pituitary gland, prostate, rectum, salivary gland (mandible), sciatic nerve, seminal vesicle, skeletal muscle, skin, spinal cord (cervical, thoracic and lumbar sternum), spleen, medullary, stomach, testis, thymus, thyroid with parathyroid, tongue, trachea, bladder, uterus and vagina.

Statistical analysis was performed as follows. The Levene test was performed to test homogeneity of variance. When the variance homogeneity is p ≦ 0.05, the variance is stabilized using the transformation. One-way analysis of variance (ANOVA) was used for analysis of continuous clinical pathology values, organ weight data, food consumption and weight data. If there is a significant difference, Dunnett's test is performed and the treated and control groups are compared in pairs. If ANOVA showed weight significance at week 1, body weight was analyzed using one-way covariate analysis (ANCOVA) with initial body weight as the covariate. If the ANCOVA were significant, the control and treated groups were compared using the corrected covariate mean analysis. Group comparisons were evaluated at a 5.0% two-tailed probability level (groups 2-5 vs group 1). Statistical analysis was performed only on data collected at or after the first day treatment. Evaluation of the data of group 6 was limited to calculating the mean and standard deviation.

Results

Slight or occasional differences were observed between the treated groups (groups 2-5) and the control group 1.

1. Observation of

On day 11, one male animal given 4.8 mg/day, restricted to hind limb use, was observed, exposing the osmotic pump, the cannula appeared unconnected; the animals were sacrificed at moribund status. On day 17, one male animal given 2.25 mg/day, restricted to hind limb use, was observed; the animals were sacrificed at moribund status. On days 20 and 21, one female given sterile water (group 6), black skin on the right ventral abdominal region and sores/scabs on the right ventral region was observed; the animals were sacrificed on day 21. All these unplanned deaths were attributed to secondary complications of the intrathecal infusion system. All other animals that survived were sacrificed as scheduled.

Animals surviving to the scheduled sacrifice had no apparent observations related to test article administration. Many clinical observations were made, but these did not show any dose relationship and were considered incidental.

Opaque eyes were observed for one female animal given 0.1 mg/day (group 2) and one female animal given 4.8 mg/day (group 4, left eye). Upon further examination, the eyes of both animals were confirmed to have keratitis. One male animal given 4.8 mg/day (group 4, left eye) was diagnosed with keratitis and one male female animal given 2.25 mg/day (group 5, left eye) was diagnosed with corneal ulceration. The occurrence of several keratitis and the occurrence of one corneal ulcer are considered to be the result of the surgical procedure, regardless of the test article administration.

Females given 2.25 mg/day (group 5) had significantly reduced body weight at weeks 1-3 compared to the group 1 control group, but the average body weight reduction did not appear to be different from that of the concurrent control (group 6) and was considered incidental, as the body weight of the group 5 animals was initially lower than that of the group 1 animals. There was no apparent test article related effect on average body weight, body weight change or food consumption.

2. Clinical and anatomic pathology

Intrathecal administration of terminally heat sterilized gabapentin had no significant effects or side effects on clinical pathology test results. The only statistical difference between the control and treated animal clinical pathology test results (i.e., lower gamma glutamyltransferases in male and female animals given 2.25 mg/day) was considered to be incidental, as animals given 4.8 mg/day had no similar effect. The most prominent findings for the 3 animals sacrificed at unscheduled intervals due to poor health, including the control females of group 6, were an increase in absolute neutrophil count and globulin concentration, and a decrease in albumin concentration. These findings are consistent with inflammatory responses and are considered incidental as dose independent and animals surviving to scheduled sacrifice do not show similar findings.

Of the 48 animals, the cannulated end was located between L3 and L6 in the subarachnoid space; in 3 animals, the cannula was located epidural. There were no differences in the weights of the test article-related organs, either by visual or microscopic observation. Some observations are related to infusion instruments and cannulas. In some animals, neurodegeneration of nerve roots is present in the area of cannula placement. Degeneration is often accompanied by gliosis. In animals that fail to survive to their scheduled sacrifice, there are inflammatory processes, including abscesses and pyogranulomas, around the infusion or cannula site or infusion pump.

There was no significant difference in glial fibrillary acidic protein immunostaining of spinal cord sections between control and high dose animals.

Discussion of the related Art

Although gabapentin lactam concentrations are elevated as a result of heating the gabapentin composition, gabapentin delivered at dosage levels of 0, 0.10, 0.25, 2.25, and 4.8 mg/day is well tolerated and is not toxic when administered intrathecally. Clinical observations, body weight changes, food consumption, ophthalmic examinations or clinical or anatomical pathology observations had no significant effect.

Claims (34)

1. A method of preparing a CNS-introduced injectable pharmaceutical composition comprising gabapentin, the method comprising:

preparing an injectable composition comprising gabapentin and a pharmaceutically acceptable carrier; and

heating the injectable composition to produce an injectable pharmaceutical composition, the heating comprising heating the injectable composition at 105-140 ℃ for 2-60 minutes.

2. The method of claim 1, wherein the heating sterilizes the composition.

3. The method of claim 1, further comprising filtering the injectable composition.

4. The method of claim 3, further comprising aseptically placing the filtered composition in a container to produce a container containing the filtered composition.

5. The method of claim 4, wherein said heating comprises heating said container containing the composition.

6. The method of claim 1, further comprising adjusting the pH of the injectable composition.

7. The method of claim 1, wherein the heating comprises autoclaving.

8. The method of claim 1, wherein the heating comprises heating the injectable composition at greater than or equal to 121 ℃ to 140 ℃ for 24 minutes.

9. The method of claim 1, wherein the heating comprises heating the injectable composition at greater than or equal to 130 ℃ to 140 ℃ for 4 minutes.

10. The method of claim 1, wherein the heating comprises heating the injectable composition at a temperature of about 118 ℃ or higher to about 140 ℃ for about 6 to about 8 minutes.

11. The method of claim 1, wherein the injectable composition is heated to F₀Is 1 or greater.

12. The method of claim 11, wherein the injectable composition is heated to F₀Is 2 or greater.

13. The method of claim 12, wherein the injectable composition is heated to F₀Is 3 or greater.

14. The method of claim 13, wherein the injectable composition is heated to F₀Is 4 or greater.

15. The method of claim 14, wherein the injectable composition is heated to F₀Is 8 or greater.

16. The method of claim 15, wherein the injectable composition is heated to F₀Is 12 or greater.

17. The method of claim 16, wherein the injectable composition is heated to F₀Is 18 or greater.

18. The method of claim 17, wherein the injectable composition is heated to F₀Is 24 or greater.

19. The method of claim 1, wherein the injectable pharmaceutical composition comprises less than or equal to 10% (w/v) gabapentin lactam.

20. The method of claim 19, wherein the injectable pharmaceutical composition comprises less than or equal to 5% (w/v) gabapentin lactam.

21. The method of claim 20, wherein the injectable pharmaceutical composition comprises less than or equal to 2% (w/v) gabapentin lactam.

22. The method of claim 21, wherein the injectable pharmaceutical composition comprises less than or equal to 1% (w/v) gabapentin lactam.

23. The method of claim 1, wherein the injectable pharmaceutical composition comprises 0.5-10% (w/v) gabapentin lactam.

24. The method of claim 1, wherein the injectable pharmaceutical composition comprises 0.1 to 100mg/ml gabapentin.

25. The method of claim 24, wherein the injectable pharmaceutical composition comprises 30-100mg/ml gabapentin.

26. The method of claim 25, wherein the injectable pharmaceutical composition comprises 80mg/ml gabapentin.

27. The method of claim 1, wherein the injectable pharmaceutical composition comprises from 10 to 50mg/ml gabapentin.

28. The method of claim 1, wherein the injectable pharmaceutical composition comprises 20-40mg/ml gabapentin.

29. The method of claim 1, wherein the injectable pharmaceutical composition comprises 30mg/ml gabapentin.

30. The method of claim 6, wherein the pH is adjusted by adding sodium hydroxide, hydrochloric acid, or both to the injectable composition.

31. A method of preparing a CNS-introduced injectable pharmaceutical composition comprising gabapentin, the method comprising:

preparing an injectable composition comprising gabapentin and a pharmaceutically acceptable carrier;

adjusting the pH of the injectable composition;

filtering the pH-adjusted injectable composition;

aseptically placing the filter-sterilized composition in a container; and

heating the composition containing vessel to produce the injectable pharmaceutical composition, the heating comprising heating the injectable composition at 105 ℃ and 140 ℃ for 2 to 60 minutes.

32. The method of claim 31, wherein the filtering comprises filtering the pH-adjusted injectable composition through a filter having a pore size of 0.22 μ ι η.

33. The method of claim 31, wherein the composition produced by the method has a sterility level equal to heating to F₀A composition of 8 or greater.

34. The method of claim 31, wherein the composition produced by the method has a sterility level equal to heating to F₀A composition of 24 or greater.