Sustained release anesthetic composition and method for preparing same

Abstract

To provide an anesthetic composition for locally administering a local anesthetic agent to a subject in need thereof.SOLUTION: An anesthetic composition has a lipid-based complex prepared by hydrating a lipid cake containing a local anesthetic agent and a lipid mixture with an aqueous buffer solution at a pH higher than 5.5. Also provided is a method for preparing an anesthetic composition using what is a simpler and more robust for large-scale manufacture and for providing a high molar ratio of local anesthetic agent to phospholipid content as compared to the prior art. This anesthetic composition has a prolonged duration of efficacy adapted to drug delivery.SELECTED DRAWING: Figure 2B

Description

[Technical Field]

[0001] Related Applications This application claims the benefit of priority to U.S. Provisional Application No. 62 / 650,912, filed March 30, 2018, which is incorporated herein by reference in its entirety.

[0002] The present disclosure relates to a drug delivery system for the delivery of sustained-release anesthetic compositions. The present disclosure relates to methods of preparing the drug delivery system. The present disclosure also relates to sustained-release pharmaceutical compositions adapted for the drug delivery system, which have a long duration of effect. [Background technology]

[0003] Several techniques for developing sustained-release local anesthetics have been reported. For example, dibucaine free base, dibucaine HCl, and bupivacaine HCl were incorporated into a polymer matrix containing the copolymer l,3-bis(p-carboxyphenoxy)propane-sebacic anhydride (1:4) to achieve sustained drug release. Meanwhile, multivesicular liposome (MVL) local anesthetics prepared by a complex procedure (Patent Document 1) have been used to deliver local anesthetics. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 8,182,835 Summary of the Invention [Problem to be solved by the invention]

[0005] To achieve high drug entrapment, i.e., improved drug efficacy through lipid-based delivery vehicles with a high drug-to-lipid ratio, conventional preparations of lipid-based formulations with the desired high drug entrapment generally involve tedious procedures and high production costs. Therefore, there is an unmet need for sustained-release local anesthetics with improved efficacy and a simplified manufacturing process. [Means for solving the problem]

[0006] The present disclosure provides a sustained-release anesthetic composition or a method for preparing the same by using one-step lyophilization to obtain a lipid cake containing a local anesthetic and a lipid mixture, and then hydrating the lipid cake with a pH-controlled buffer to form a lipid-based complex containing the local anesthetic and the lipid mixture. The sustained-release anesthetic composition provides rapid onset of anesthesia and long duration of local anesthesia with minimal toxicity. In some embodiments, the local anesthetic is an amide-type anesthetic.

[0007] In some embodiments, the local anesthetic is ropivacaine. Other local anesthetics that may be used include lidocaine, bupivacaine, and levobupivacaine.

[0008] In some embodiments, the present disclosure provides a simple and reliable manufacturing process for preparing an anesthetic composition for topical administration of a local anesthetic to a subject in need thereof, wherein the hydration step in the process can be carried out in an ambient environment.

[0009] In some embodiments, the lipid cake is formed with phospholipids so that it can be rehydrated with a buffer to obtain the desired sustained release anesthetic composition with high relative efficacy of local anesthetic at ambient temperature without increasing the temperature, which would cause extra cost in energy or inconvenience in clinical use.

[0010] According to the present disclosure, the lipid cake comprises a local anesthetic and a lipid mixture comprising at least one neutral saturated phospholipid comprising a saturated fatty acid having a long carbon chain of 18 carbons or less, thereby allowing the lipid cake to be easily stored and the anesthetic composition to be prepared prior to clinical use by combining the lipid cake with a buffer at a manufacturing facility or under predetermined controlled conditions, for example, at ambient temperature. In some embodiments, the saturated fatty acid having a long carbon chain has 14, 16, or 18 carbons.

[0011] In some embodiments, a lipid cake according to the present disclosure is prepared by dissolving non-polar ropivacaine, phospholipids, and cholesterol in a solvent system, such as tert-butanol alone or a tert-butanol / water co-solvent, followed by removal of the solvent system using freeze-drying techniques.

[0012] The pH value of the pharmaceutically acceptable buffer may nevertheless be selected to adjust the ratio of entrapped to unentrapped local anesthetic in the anesthetic composition. In certain embodiments, the phospholipid (mol) in the lipid-based complex of the anesthetic composition drug :mol phospholipid The molar ratio of local anesthetic to α-aminobutyric acid (C ) is at least 0.5:1, providing a sufficient amount of local anesthetic to a subject in need thereof to extend the duration of anesthesia after local administration in vivo. Furthermore, limiting the amount of untrapped local anesthetic reduces the peak plasma concentration (C ). max ) Rapid onset of anesthesia can be achieved with minimal exposure.

[0013] In some embodiments, the present disclosure also provides a method of providing analgesia or pain relief in a subject in need thereof, comprising administering to the subject an anesthetic composition according to the present disclosure.

[0014] In some embodiments, the present disclosure provides a method for managing pain in a subject, or a method for the prophylactic treatment of pain, comprising administering to the subject an anesthetic composition according to the present disclosure.

[0015] Other objects, advantages and novel features of the present disclosure will become more apparent from the following detailed description when considered in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0016] [Figure 1A] 1A is a graph showing 50% paw withdrawal thresholds in the Von Frey test, in which an anesthetic composition according to the present disclosure (ropivacaine composition) is the inventors' test article, and ropivacaine injection solution (unformulated ropivacaine) and commercially available extended-release liposomal bupivacaine (ER bupivacaine) are used as reference articles. Saline, ropivacaine composition, ropivacaine injection, and ER bupivacaine were administered intraplantarly after paw incision. Error bars represent standard error of the mean (SEM). *: P<0.05 compared with the ER bupivacaine group; BBL = pre-surgery baseline; ABL = post-surgery baseline. [Figure 1B] Figure 1B is a graph showing the percentage of maximum possible effect (%MPE) calculated from the 50% paw withdrawal threshold using the formula %MPE = (threshold after treatment - ABL) / (BBL - ABL) × 100%; error bars represent standard error of the mean (SEM); *: P < 0.05 compared with the ER bupivacaine group. An MPE of more than 30% is considered effective; [Figure 2A] 2A is a graph showing 50% paw withdrawal thresholds from the Von Frey test, in which an anesthetic composition according to the present disclosure (ropivacaine composition) is the inventors' test article and ER bupivacaine is used as the reference article. Saline, ropivacaine composition, and ER bupivacaine were administered by sciatic nerve block. Error bars represent the standard error of the mean (SEM). [Figure 2B]Figure 2B is a graph showing the percentage of maximum possible effect (%MPE) calculated from the 50% paw withdrawal threshold by the formula %MPE = (threshold after treatment - pre-dose baseline) / (threshold cut-off - pre-dose baseline) x 100%, where the cut-off threshold was 15 g. Error bars represent the standard error of the mean (SEM). An MPE greater than 30% was considered effective. DETAILED DESCRIPTION OF THE INVENTION

[0017] As used above, and throughout this disclosure, the following terms, unless otherwise indicated, shall be understood to have the following meanings:

[0018] As used herein, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise.

[0019] All numbers herein, when referring to measurable values ​​such as amounts, temporal durations, and the like, unless otherwise specified, may be understood to be modified by "about," which means to encompass variations of ±10%, ±5%, ±1%, or ±0.1% from the specified value, such variations being appropriate to obtain the desired amount of drug.

[0020] "Association efficiency" (AE) represents the amount of drug substance entrapped in the formed lipid-based complex with the local anesthetic in the anesthetic composition, and is calculated by the ratio of the amount of drug substance in the separated lipid-based complex to the amount of the drug substance in the anesthetic composition. The separated lipid-based complex can be obtained from the anesthetic composition by any method known in the art. In some embodiments, the separated lipid-based complex is obtained from an anesthetic composition prepared by centrifugation, e.g., conventional centrifugation, density gradient centrifugation, differential centrifugation, or by filtration, e.g., diafiltration, gel filtration, membrane filtration.

[0021] As used herein, the terms "treat," "treating," or "treatment" include preventative (e.g., prophylactic), palliative, and curative methods, uses, or results. The terms "treatment" or "treatments" can also refer to compositions or medicaments. The term "treating" encompasses reducing or delaying one or more symptoms or signs of pain, or complete amelioration of pain, as detected by known techniques. Art-recognized methods are available for assessing pain and pain symptoms, such as pain scores and 50% paw withdrawal thresholds. For example, the disclosed methods of use of sustained-release anesthetic compositions are considered target treatment if there is at least a 1% reduction in one or more symptoms of pain in a subject compared to a subject before treatment or a control subject. Thus, the reduction can be about a 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100% reduction, or any amount between these values.

[0022] local anesthetic As used herein, "local anesthetic" includes one or more substances that cause loss of sensation in a localized area of ​​a subject, caused by inhibition of excitation at nerve endings or inhibition of the conduction process in peripheral nerves. In some embodiments, the local anesthetic is an amide anesthetic. A typical amide anesthetic structure includes a lipophilic portion and a hydrophilic portion connected by an -NHCO- bond. Suitable amide anesthetics include, but are not limited to, lidocaine, bupivacaine, levobupivacaine, ropivacaine, mepivacaine, pyrrocaine, articaine, and prilocaine. In certain embodiments, the local anesthetic is ropivacaine base.

[0023] lipid cake The lipid cake comprises a lipid mixture and one or more local anesthetics, which can be manufactured and stored for extended periods to extend the shelf life of the composition, and hydrated immediately prior to clinical use in ambient conditions. The lipid mixture can contain one or more phospholipids that do not contain sterols, or one or more phospholipids with a molar percentage of sterol to cholesterol of 50% or less based on the total lipid mixture. In certain embodiments, the molar percentage of cholesterol based on the lipid mixture is about 0% to 50%, and optionally about 25% to 40%, or 33% to 35%. In some embodiments, the phospholipid(s) and cholesterol are in a molar ratio of 1:1 to 3:1.

[0024] The lipid cake can be prepared by 1) dissolving a lipid mixture and one or more local anesthetics in a solvent system to form a homogeneous solution containing one or more solvents, and 2) removing the solvent(s) to solidify the formulation of the lipid mixture and local anesthetic(s). Solvent removal can be performed using known techniques such as freeze-drying (lyophilization). Examples of solvent systems suitable for freeze-drying include, but are not limited to, tert-butanol / water co-solvent systems with or without other non-aqueous solvents such as tert-butanol and acetone, acetonitrile, ethanol, n-propanol, isopropanol, n-butanol, methanol, dichloromethane, dimethyl sulfoxide, and carbon tetrachloride.

[0025] Anesthetic Composition The term "anesthetic composition" refers to a product suitable for topical administration. In certain embodiments, the anesthetic composition comprises a lipid-based complex and an unentrapped local anesthetic. In some embodiments, the lipid-based complex comprises multilamellar vesicles and a local anesthetic entrapped in the multilamellar vesicles. The terms "entrap" or "entrapment" refer to the bilayer membrane of the multilamellar vesicles encapsulating, embedding, or associating the target drug substance.

[0026] The particle size distribution of lipid-based complexes according to the present disclosure can be determined by various methods known in the art. In some embodiments, the mean particle size of the lipid-based complexes of the anesthetic composition is 1 μm or greater; optionally, 5 μm or greater, e.g., in the range of 5 μm to 50 μm, or 10 μm to 25 μm. Alternatively, the volume median particle size (D50) of the lipid-based complexes of the anesthetic composition is 1 μm or greater, and optionally, 5 μm or greater, e.g., in the range of 5 μm to 50 μm, 5 μm to 40 μm, 5 μm to 30 μm, 5 μm to 20 μm, or 5 μm to 15 μm. In some embodiments, the median particle size (D50), which refers to the particle size at which the cumulative percentage of lipid-based complexes made of aggregated particles is 50% in the cumulative particle size distribution, is 5 μm or greater, or 7 μm or greater. In some embodiments, the median particle size (D50), which refers to the particle size at which the cumulative percentage of lipid-based complexes made of aggregated particles is 50% in the cumulative particle size distribution, is 25 μm or less, 20 μm or less, or 15 μm or less.

[0027] In some embodiments, the particle size at 90% of the cumulative particle size distribution (D90) of the lipid-based complex of the anesthetic composition is 10 μm or more, for example, in the range of 10 μm to 300 μm, 20 μm to 200 μm, or 20 μm to 100 μm. Furthermore, the lower limit of D90 is not particularly limited to 25 μm or more or 30 μm or more. In addition, the shape of aggregated particles of the lipid-based complex for improving the aggregation efficiency per unit dose is not particularly limited.

[0028] To prepare the anesthetic composition for use, the lipid cake is hydrated with an aqueous buffer solution at a pH of 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, or 7.0 or greater. In some embodiments, the aqueous buffer solution has a pH range of 5.5-8.0, optionally 6.0-7.8, 6.0-7.5, 6.3-7.5, 6.5-7.5, 6.7-7.5, or 6.8-7.5.

[0029] Suitable aqueous buffers according to the present disclosure include, but are not limited to, citrate, acetate, malate, piperazine, succinate, 2-(N-morpholino)ethanesulfonic acid (MES), histidine, bis-tris, phosphate, ethanolamine, N-(2-acetamido)iminodiacetic acid (ADA), carbonate, N-(2-acetamido)-2-aminoethanesulfonic acid (ACES), 1,4-piperazinediethanesulfonic acid (PIPES), 3-morpholino-2-hydroxypropanesulfonic acid (MOPSO), imidazole, N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES), 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid (HEPES), triethanolamine, lysine, tris, and glycylglycine. The amount of unentrapped amide-type anesthetic in the composition can be adjusted based on the distribution coefficient of the anesthetic by selecting an appropriate pH value of the aqueous buffer based on the clinical indication and the total injection dose.

[0030] In some embodiments, the aqueous buffer solution contains histidine at a concentration ranging from 1 mM to 200 mM, 10 mM to 150 mM, or 40 mM to 120 mM.

[0031] In some embodiments, the aqueous buffer solution comprises phosphate at a concentration ranging from 1 mM to 200 mM, 10 mM to 180 mM, or 40 mM to 160 mM.

[0032] The amount of unentrapped amide anesthetic is a function of the association efficiency (AE) of the anesthetic composition, as determined by centrifugation. Mathematically, the amount of unentrapped amide anesthetic is expressed as: A untrapped =A total ×(1-AE) In the formula, A untrapped is the amount of untrapped amide-type anesthetic; A totalis the total amount of amide anesthetic in the anesthetic composition; AE is the amount of amide anesthetic entrapped in the lipid-based complex divided by the total amount of amide anesthetic in the anesthetic composition. AE according to the present disclosure is at least 60%, optionally 70% to 99%.

[0033] In some embodiments, the molar ratio of amide-type anesthetic to phospholipid in the lipid-based complex (mol drug :mol phospholipid , D:PL) is at least 0.5:1, including but not limited to 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, or 1.5:1. In certain embodiments, the median diameter (D50) of the lipid-based complexes is 1 μm or more, optionally 5 μm or more, e.g., in the range of 5 μm to 50 μm, 5 μm to 40 μm, 5 μm to 30 μm, 5 μm to 20 μm, or 5 μm to 15 μm; and the D90 of the lipid-based complexes is 10 μm or more, e.g., in the range of 10 μm to 300 μm, 20 μm to 200 μm, or 20 μm to 100 μm.

[0034] The amide anesthetic concentration of the anesthetic composition should be greater than 2 mg / mL to achieve clinical therapeutic benefit. Suitable amide anesthetic concentrations include, but are not limited to, 2 mg / mL to 30 mg / mL and 10 mg / mL to 20 mg / mL. The limited amount of untrapped anesthetic in the anesthetic composition of the present disclosure can provide the advantage of achieving a higher maximum tolerated dose (depending on the plasma anesthetic concentration causing central nervous system and cardiovascular toxicity) and can be used to provide a rapid onset of action.

[0035] For clinical use, the AE in certain embodiments of the present disclosure ranges from 70% to 99.9%, 75% to 99.5%, 80% to 99.5%, 85% to 99.5%, 90% to 99.5%, or 95% to 99.5%. The remaining lipid-based complex acts as a depot to gradually release the amide-type anesthetic into the local environment in a manner that maintains a therapeutically effective dose at the local site. In some embodiments, the half-life of ropivacaine from a single subcutaneous administration of a ropivacaine composition according to the present disclosure is extended by at least 10-fold compared to the half-life of unformulated ropivacaine. The duration of anesthetic effect following administration of a ropivacaine composition of the present disclosure extends significantly beyond that of unformulated ropivacaine.

[0036] multilamellar vesicles The term "multilamellar vesicle" as used herein refers to a particle characterized by having an aqueous internal space separated from the external medium by one or more bilayer membranes forming the vesicle.The bilayer membrane of multilamellar vesicles is typically formed by lipids, i.e., amphiphilic molecules of synthetic or natural origin that contain spatially separated hydrophobic and hydrophilic domains.In certain embodiments of the present disclosure, the multilamellar vesicle has a membrane formed by multiple lipid bilayers.

[0037] Generally, the bilayer membrane of a multilamellar vesicle comprises a lipid mixture including phospholipids, diglycerides, dialiphatic chain lipids such as dialiphatic glycolipids; single lipids such as sphingomyelin and glycosphingolipids; steroids such as cholesterol and its derivatives; and combinations thereof. Examples of phospholipids according to the present disclosure include, but are not limited to, 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1-palmitoyl-2-stearoyl-sn-glycero-3-phosphocholine (PSPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC), 1,2-di Stearoyl-sn-glycero-3-phosphocholine (DSPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), hydrogenated soy phosphatidylcholine (HSPC), 1,2-dimyristoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (DMPG), 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (DP PG), 1-palmitoyl-2-stearoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (PSPG), 1,2-distearoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (DSPG), 1,2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DOPG), 1,2-dimyristoyl-sn-glycero-3-phospho -L-serine (sodium salt) (DMPS), 1,2-dipalmitoyl-sn-glycero-3-phospho-L-serine (sodium salt) (DPPS), 1,2-distearoyl-sn-glycero-3-phospho-L-serine (sodium salt) (DSPS), 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS), 1,2-dimyristoyl-sn-glycero-3-phosphate (sodium salt) (DMPA), 1,2-Dipalmitoyl-sn-glycero-3-phosphate (sodium salt) (DPPA), 1,2-distearoyl-sn-glycero-3-phosphate (sodium salt) (DSPA), 1,2-dioleoyl-sn-glycero-3-phosphate (sodium salt) (DOPA), 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE), 1 , 2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-myo-inositol) (ammonium salt) (DPPI), 1,2-distearoyl-sn-glycero-3-phosphoinositol (ammonium salt) (DSPI), 1,2-dioleoyl-sn-glycero-3-phospho-(1'-myo-inositol) (ammonium salt) (DOPI), cardiolipin, L-α-phosphatidylcholine (EPC), and L-α-phosphatidylethanolamine (EPE).

[0038] Examples of phospholipids include, but are not limited to, dimyristoylphosphatidylcholine (DMPC), 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), dipalmitoylphosphatidylcholine (DPPC), diolylphosphatidylglycerol (DOPG), 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC), 1,2-dioleoyl-sn-glycero-3-phosphatidylserine (DOPS), diolylphosphatidic acid (DOPA), egg phosphatidylcholine (egg PC), phosphatidylethanolamine (egg PE), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylethanolamine (POPE), cardiolipin, and 1,2-dimyristoyl-sn-glycero-3-phosphate (sodium salt) (DMPA).

[0039] Suitable phospholipids according to the present disclosure are saturated phospholipids derived from two saturated long carbon chain fatty acids, each fatty acid having a carbon chain length of at least 12 and no more than 20 carbons. In some embodiments, suitable saturated phospholipids according to the present disclosure are selected from the group consisting of DLPC, DMPC, DPPC, and combinations thereof.

[0040] In some embodiments, the lipid mixture comprises a suitable phospholipid according to the present disclosure, such as a positively or negatively charged phospholipid and a determined amount of an unsaturated phospholipid, wherein the determined amount is less than 10% molar percent, e.g., 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1%, based on the total amount of phospholipid.

[0041] Local anesthesia and pain prevention Anesthetic compositions according to the present disclosure are for use in local anesthesia and can be administered perineurally or into surgical wounds to treat pain. In some embodiments, the pain is postoperative pain or labor pain. In some embodiments, the anesthetic composition is administered subcutaneously, intradermally, or intramuscularly to treat a painful condition in a subject in need thereof.

[0042] In some embodiments, local anesthesia includes circumferential infiltration and infiltration anesthesia. Circumferential infiltration is directed at injecting a local anesthetic around the border of the area to be anesthetized, without attempting to identify the location of a specific nerve. Infiltration anesthesia is directed at injecting a local anesthetic directly into the area of ​​the terminal nerve endings.

[0043] In some embodiments, compositions according to the present disclosure are administered as nerve blocks in a subject in need thereof as a preventative treatment of a painful condition, such as administration before surgery to treat post-operative pain.

[0044] Nerve blocks involve introducing an agent near or into a peripheral nerve to reduce pain or provide numbness.

[0045] Types of nerve blocks include, but are not limited to, motor, sensory, differential, and autonomic blocks, and further include, but are not limited to, brachial plexus (axillary, interscalene, supraclavicular, infraclavicular), individual upper extremity nerve blocks (median, radial, ulnar, musculocutaneous, axillary), ischial, ankle, metatarsal, oral, femoral, popliteal, saphenous, distal, digital, deep peroneal, superficial peroneal, tibial, peroneal, peroneal, and saphenous blocks.

[0046] The disclosure will be further described with reference to the following specific, non-limiting examples. [Example]

[0047] The following examples illustrate the preparation and properties of certain embodiments of the present disclosure.

[0048] Example 1 Preparation of ropivacaine compositions with various phospholipids Phospholipids, including DLPC, DMPC, DPPC, DOPG, DOPC, DOPS, DOPA, egg PC, egg PE, POPE, cardiolipin, and DMPA, were purchased from NOF Corporation (Tokyo, Japan) or Lipoid GmbH (Ludwigshafen, Germany). Cholesterol was purchased from Sigma-Aldrich (Darmstadt, Germany) or Dishman Pharmaceuticals and Chemicals (Gujarat, India). Ropivacaine was purchased from Apollo Scientific (Cheshire, UK) or Dishman Pharmaceuticals and Chemicals. All other chemicals were purchased from Sigma-Aldrich.

[0049] To prepare lipid cakes, ropivacaine was combined with various lipid mixtures, as shown in Table 1, at a drug-to-phospholipid (D:PL) ratio of 1.458 μmol / μmol, i.e., phospholipid:cholesterol:ropivacaine = 2:1:2.9. The lipid and ropivacaine were mixed and then dissolved in tert-butanol or a tert-butanol / water cosolvent system (1 / 1, vol / vol) to form liquid structures. Each liquid structure sample was frozen for 30–60 min and then lyophilized overnight to obtain lipid cakes.

[0050] To prepare the lipid structure for the vehicle control, a lipid mixture with a 2:1 molar ratio of DMPC:cholesterol was weighed and then dissolved in tert-butanol. The resulting sample was frozen for 60 minutes and then lyophilized overnight to obtain the vehicle lipid cake.

[0051] The lipid cake was hydrated in 50 mM histidine buffer at pH 6.5 at a temperature not lower than 25°C / ambient temperature (AT) for 2-10 minutes to form the vehicle and ropivacaine compositions, respectively, followed by characterization of association efficiency and particle size distribution.

[0052] Example 2 Characterization of ropivacaine compositions The association efficiency (AE) of each formulation described in Example 1 was determined as follows: 200 microliters of each ropivacaine composition was transferred to a centrifuge and spun at 3000 × g for 5 minutes at 4 °C. After decanting the supernatant, the separated lipid-based complex was obtained and resuspended to a final volume of 200 μL. For each drug substance (e.g., ropivacaine), a reference absorbance standard was established based on a solution of the test drug substance of known concentration. The amount of drug substance in both the initial ropivacaine composition and the separated lipid-based complex was measured using an ultraviolet / visible (UV / Vis) spectrophotometer. AE represents the ratio of the amount of drug substance in the separated lipid-based complex to the amount of drug substance in the initial ropivacaine composition. The D:PL of the separated lipid-based complex was calculated by multiplying the D:PL of the lipid cake by the AE and was designated as the "resulting D:PL."

[0053] The particle size of each ropivacaine composition was measured using a laser diffraction particle size analyzer (LA-950V2, Horiba or Mastersizer 3000, Malvern). The volume median diameter (D50) of lipid-based complexes containing ropivacaine formed by hydrating the lipid cake with 50 mM histidine buffer (pH 6.5) or phosphate buffer (pH 7.0) was tested and compared in Table 1.

[0054] Lipid cakes containing DMPC, DLPC, or DPPC showed very similar AEs (90%, 90%, and 92%, respectively). However, the median diameters (D50) of the lipid-based complexes containing ropivacaine were different. The D50s of the resulting lipid-based complexes containing ropivacaine in the ropivacaine compositions from the hydration of lipid cakes with DMPC, DLPC, and DPPC were 6.6 ± 0 to 12.7 ± 0.4, 7.8 ± 0.1, and 14.9 ± 0.1 μm, respectively. A summary of the results is shown in Table 1.

[0055] [Table 1]

[0056] Example 3 Preparation of ropivacaine compositions by combining various phospholipids The sources of phospholipids, cholesterol, ropivacaine, and all other chemicals were described in Example 1.

[0057] To prepare the lipid cakes, ropivacaine was combined with various lipid mixtures in a molar ratio of 2:1:2.9 phospholipid:cholesterol:ropivacaine. The phospholipids were a combination of DMPC and one of the other phospholipids listed in Table 2 in a molar ratio of 1.8:0.2 DMPC:other phospholipid. The lipid and ropivacaine were mixed and then dissolved in tert-butanol to form liquid structures. Each liquid structure sample was frozen for 30–60 min and then lyophilized overnight to obtain lipid cakes.

[0058] The lipid cake was hydrated with 50 mM histidine buffer at pH 6.5 at ambient temperature to form the ropivacaine composition, followed by characterization of association efficiency and particle size distribution.

[0059] The resulting lipid-based complexes containing ropivacaine in ropivacaine compositions from the hydration of lipid cakes consisting of combinations of DMPC / DLPC, DMPC / DPPC, DMPC / egg PC, DMPC / egg PE, or DMPC / POPE showed very similar AEs (90%, 91%, 91%, 91%, and 91%, respectively). The mean diameters (D50) of the lipid-based complexes containing ropivacaine in ropivacaine compositions also showed similar results. The D50s of the resulting lipid-based complexes in ropivacaine compositions from the hydration of lipid cakes consisting of combinations of DMPC / DLPC, DMPC / DPPC, DMPC / egg PC, DMPC / egg PE, or DMPC / POPE were 11.4 ± 0.3, 14.3 ± 0.1, 11.6 ± 0.0, 11.5 ± 0.0, and 11.0 ± 0.3 μm, respectively. A summary of the results is shown in Table 2.

[0060] [Table 2]

[0061] Example 4 Anesthetic effects in a rat paw incision model Sprague-Dawley rats were used to evaluate the effects of anesthesia after paw incision as described in Pain. 1996 Mar;64(3):493-501. The rat housing facility was operated on a 12-hour light / 12-hour dark circadian cycle, and experiments were conducted during the diurnal portion of the circadian cycle only. A ropivacaine composition (ropivacaine composition) as one embodiment of an anesthetic composition according to the present disclosure was prepared according to Example 1, in which a lipid cake of DMPC:cholesterol:ropivacaine = 2:1:2.9 was hydrated with 50 mM histidine buffer at pH 6.8. Unformulated ropivacaine was prepared by dissolving ropivacaine in 19.0 mg / mL water for injection. A commercially available FDA-approved sustained-release liposomal bupivacaine formulation (ER bupivacaine) was purchased from Pacira Pharmaceuticals, Inc. The in vivo efficacy of ropivacaine compositions, plain ropivacaine, saline, and ER bupivacaine was compared following intraplantar injection after paw incision at doses of 1.9 mg per incision for plain ropivacaine and ropivacaine compositions, and 1.33 mg per incision for ER bupivacaine (isotonic dose).

[0062] Twenty-seven rats were measured for pre-surgery baseline (BBL) measurements between days -1 and -3 before surgery; 27 rats were measured for post-surgery baseline (ABL) measurements 30 minutes after surgery. Rats with a BBL baseline threshold greater than 9 g and an ABL baseline threshold less than 4 g were used for formal testing. A final total of 20 rats were randomly assigned to four groups (five rats per group). While anesthetized with 2-3.5% isoflurane in 100% oxygen, each rat underwent a 1-cm longitudinal plantar incision in the left hind paw, and three additional incisions were made in the fascia. Each rat received a single intraplantar injection of saline (100 μl), ropivacaine composition (100 μl of 19.0 mg / mL), ER bupivacaine (100 μl of 13.3 mg / mL), or unformulated ropivacaine (100 μl of 19.0 mg / mL). The 50% paw withdrawal threshold for each rat was obtained using the Dixon up-down method at the BBL time point (days −1 to −3), the ABL time point, and at designated time points (0.5, 1, 2, 3, 4, 5, 6, 7, and 24 h) after intraplantar injection.

[0063] The anesthetic effects of formula ropivacaine (diamonds), plain ropivacaine (triangles), ER bupivacaine (squares), and saline (circles) after paw incision are shown in Figure 1A and Figure 1B. The mean 50% paw withdrawal threshold for each treatment group was graphed, and data presented as 50% paw withdrawal threshold (g) were plotted against time (Figure 1A). The percentage of maximum possible effect (%MPE) for each treatment was calculated from the 50% paw withdrawal threshold using the formula %MPE = (threshold after treatment The %MPE was calculated using the formula: (-ABL) / (BBL-ABL) × 100%. The %MPE for each treatment was graphed, and the data, expressed as %MPE, were plotted against time (Figure 1B). The ropivacaine composition and unformulated ropivacaine had similar onset of action, with withdrawal thresholds increasing from 1.83 g to 13.00 g and from 1.74 g to 11.47 g, respectively, at T = 0.5 hours. The ropivacaine composition also had a faster onset of action than ER bupivacaine, showing an increase in withdrawal threshold from 1.80 g to 6.51 g at T = 0.5 hours. The ropivacaine composition produced the longest analgesic effect (lasting at least 6 hours) compared with ER bupivacaine (less than 5 hours).

[0064] Example 5 Anesthetic effect of cuff implantation in a rat model of sciatica Sprague-Dawley rats were used to evaluate the effects of anesthesia after implantation of a cuff on the sciatic nerve as described in Pain. 1999 Oct;83(1):37-46. The rat housing facility was operated on a 12-hour light / 12-hour dark circadian cycle, and experiments were conducted during the diurnal portion of the circadian cycle only. A ropivacaine composition (ropivacaine composition) as one embodiment of an anesthetic composition according to the present disclosure was prepared according to Example 1, in which a lipid cake of DMPC:cholesterol:ropivacaine = 2:1:2.9 was hydrated with 50 mM histidine buffer at pH 6.8. A commercially available FDA-approved sustained-release liposomal bupivacaine formulation (ER bupivacaine) was purchased from Pacira Pharmaceuticals, Inc. The in vivo efficacy of ropivacaine compositions, ER bupivacaine, and saline was compared following sciatic nerve injection after implantation of a cuff over the sciatic nerve in rats at doses of 25 mg / kg for ropivacaine compositions and 25 mg / kg and 35 mg / kg for ER bupivacaine.

[0065] While under anesthesia, a 3-4 mm PE 60 or PE 90 tube was placed over the sciatic nerve in the left leg. After cuffing, the muscle and skin were apposed with two to three sutures. Post-cuff baseline (2-3 weeks after cuff implantation) samples were collected to confirm pain induction. Rats demonstrating a baseline threshold of less than 4 g were used for formal testing. A total of 21 rats were randomly divided into three groups (7 rats each) and administered ropivacaine composition (25 mg / kg), ER bupivacaine (25 mg / kg), or ER bupivacaine (35 mg / kg) via sciatic nerve block. Four rats were treated with saline as controls. The 50% paw withdrawal threshold for each rat was obtained using the Dixon up-down method before administration and at designated time points (1, 3, 4, 5, 6, 7, 8, and 9 hours) after administration.

[0066] The anesthetic effects of ropivacaine composition (25 mg / kg, open triangle), ER bupivacaine (25 mg / kg, open circle; 35 mg / kg, closed inverted triangle), and saline (closed circle) after administration are shown in Figures 2A and 2B. The mean 50% paw withdrawal threshold for each treatment group was graphed, and data presented as 50% paw withdrawal threshold (g) were plotted against time (Figure 2A). The percentage of maximum possible effect (%MPE) of each treatment was calculated from the 50% paw withdrawal threshold using the formula %MPE = (threshold after treatment - Pre-administration baseline) / (Threshold Cut-off The %MPE was calculated using the following formula: (-pre-administration baseline) × 100%. The cutoff threshold was 15 g in this study. The %MPE for each treatment was graphed, and the data expressed as %MPE were plotted against time (Figure 2B). The ropivacaine composition produced the longest analgesic effect (more than 9 hours) compared to ER bupivacaine (less than 8 hours) for both the 25 mg / kg and 35 mg / kg groups. A percentage of MPE greater than 30% was considered effective.

Claims

1. 1. An anesthetic composition for topically administering a local anesthetic to a subject in need thereof, comprising: an amide-type anesthetic in its free base form; and Lipid mixture comprising at least one neutral saturated phospholipid and a sterol at pH 6.0-8.0 Including, the amide anesthetic is bupivacaine, levobupivacaine, or mepivacaine; the at least one neutral saturated phospholipid is derived from saturated fatty acids, each fatty acid independently comprising a carbon chain having 18 or fewer carbon atoms; the lipid-based complexes have an average diameter of 1 μm or greater; and An anesthetic composition, wherein the molar ratio of the amide-type anesthetic to phospholipid in the lipid-based complex is at least 0.5:

1.

2. 2. The anesthetic composition of claim 1, wherein the neutral saturated phospholipid is selected from the group consisting of dimyristoylphosphatidylcholine (DMPC), 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), and dipalmitoylphosphatidylcholine (DPPC).

3. 10. The anesthetic composition of claim 1, wherein the lipid mixture further comprises an unsaturated phospholipid present in an amount less than 10% mole percent based on the amount of total phospholipid.

4. 4. The anesthetic composition of claim 3, wherein the unsaturated phospholipid is 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylethanolamine (POPE), phosphatidylethanolamine (egg PE), or egg phosphatidylcholine (egg PC).

5. 2. The anesthetic composition of claim 1, wherein the molar percentage of sterols in the lipid mixture is 50% or less.

6. 2. The anesthetic composition of claim 1, wherein the at least one neutral saturated phospholipid and the sterol are in a molar ratio of 1:0.01 to 1:

1.

7. 2. The anesthetic composition of claim 1, wherein the sterol is cholesterol.

8. 10. The anesthetic composition of claim 1, wherein the lipid-based complexes have a median diameter in the range of 5 μm to 50 μm.

9. 9. The anesthetic composition of claim 8, wherein the lipid-based complexes have a median diameter in the range of 5 μm to 20 μm.

10. 10. The anesthetic composition of claim 1, wherein the anesthetic composition has an association efficiency (AE) of the amide-type anesthetic of at least 60%.

11. 2. The anesthetic composition of claim 1, wherein the anesthetic composition has an AE of 70% to 99% of the amide-type anesthetic.

12. 10. The anesthetic composition of claim 1, wherein the molar ratio of the amide-type anesthetic to phospholipid in the lipid-based complex ranges from 0.5:1 to 2:

1.

13. 10. The anesthetic composition of claim 1, wherein the molar ratio of the amide-type anesthetic to phospholipid in the lipid-based complex ranges from 0.7:1 to 2:

1.

14. 10. The anesthetic composition of claim 1, wherein the molar ratio of the amide-type anesthetic to phospholipid in the lipid-based complex ranges from 0.7:1 to 1.5:

1.

15. 1. An anesthetic composition for use in the treatment of pain in a subject in need of anesthesia, comprising: (a) Below: an amide-type anesthetic in its free base form; and Lipid mixture comprising at least one neutral saturated phospholipid and a sterol at a pH of 6.0 to 8.0, the amide anesthetic is bupivacaine, levobupivacaine, or mepivacaine; the at least one neutral saturated phospholipid is derived from saturated fatty acids, each fatty acid independently comprising a carbon chain having 18 or fewer carbon atoms; The anesthetic composition, wherein the lipid-based complex has an average diameter in the range of 1 μm to 30 μm, and the molar ratio of the amide-type anesthetic to phospholipid in the lipid-based complex is at least 0.5:

1.

16. 16. The anesthetic composition of claim 15, wherein the saturated phospholipid is selected from the group consisting of dimyristoylphosphatidylcholine (DMPC), 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), and dipalmitoylphosphatidylcholine (DPPC).

17. 16. The anesthetic composition of claim 15, wherein the anesthetic composition is administered perineurally or into a surgical wound.

18. 16. The anesthetic composition of claim 15, wherein the pain is post-operative pain or labor pain.

19. 16. The anesthetic composition of claim 15, wherein the anesthetic composition is administered as a nerve block.

20. 16. The anesthetic composition of claim 15, wherein the anesthetic composition is administered as a field block.

21. 16. The anesthetic composition of claim 15, wherein the anesthetic composition is administered as an infiltration anesthetic.

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