PHARMACEUTICAL PRODUCTS PROVIDING ENHANCED ANALGESIA

Abstract: An analgesic composition comprising capsaicin or a capsaicin analogue and an analgesic selected from the class of non-steroidal anti-inflammatory, antipyretic and analgesic drugs is disclosed. This combination has been found to exhibit unexpectedly enhanced analgesic activity in humans and lower animals without a corres­ ponding increase in undesirable side effects.

Description: The present invention relates to analgesic compositions comprising capsaicin or a capsaicin analog combined with a drug selected from the class of non-steroidal anti-inflammatory, antipyretic and analgesic compounds. These compositions, when administered to humans or lower animals, provide a synergistic analgesic effect while minimizing undesirable side effects and toxicity. Capsaicin and its derivatives appear to produce an analgesic effect through a mechanism largely unrelated to that of the other two categories of analgesics, opioids (narcotics) and non-steroidal analgesics (aspirin-like drugs). Since both capsaicin and the non-steroidals produce an analgesic effect, although apparently through different mechanisms, it might be expected that their combined effect would be at best additive. However, tests have shown that the analgesic effect of the combination is not merely the sum of the effects of each component, but rather an unexpected, greatly enhanced synergistic effect. Furthermore, the undesirable side effects of the two categories of analgesics are not closely related and the addition of the second analgesic does not appear to potentiate the side effects of the first. It is therefore possible to combine the two analgesics in such a dosage as to provide greatly enhanced analgesia with no enhancement of side effects. Depending on the dosages employed, the capsaicin may either potentiate the degree of analgesia beyond that obtainable using the non-steroidal alone, or it may induce analgesia at dosages where no analgesic effect is obtained from either component alone. Traditionally, analgesics have fallen into two broad categories. Simple, non-narcotic analgesics, such as aspirin, which appear to work by inhibition of prostaglandin synthetase, are effective against pain of integumental origin such as headache and muscle aches, but are often ineffective in controlling deeper, more intense pain. Furthermore, they may cause undesirable side effects even at therapeutic dosages. The most common of these side effects is a propensity to induce dyspepsia and gastrointestinal bleeding. At higher dosages, the salicylates may have toxic effects on the central nervous system consisting of stimulation (including convulsions) followed by depression. Headache, dizziness, mental confusion, hearing difficulties and hyperventilation may also occur. Gastrointestinal symptoms may include epigastric distress, nausea and vomiting. The narcotic analgesics appear to work through interaction with the endorphin/enkephalin receptor system of the central nervous system and are useful in controlling pain which is too intense to be controlled by the weaker, non-narcotic analgesics. However, centrally-acting narcotic analgesics have several serious undesirable side effects, including the development of physical dependence and tolerance, sedation, respiratory depression, hypotension, increase in cerebrospinal fluid pressure, nausea, vomiting and constipation. In some patients, particularly the chronically ill, the narcotic side effects make it impossible to administer dosages sufficient to adequately control pain over the required time period. This invention combines capsaicin or a capsaicin analog with a drug from the class of non-narcotic, non-steroidal anti-inflammatory, antipyretic and analgesic compounds producing a synergistic increase in analgesia without a corresponding increase in side effects. The degree of analgesia produced by this combination has been found in some cases to be equivalent to that formerly obtainable only through the use of narcotics. Thus, the claimed combination makes it possible to control pain which is too severe to be adequately controlled by the non-steroidals alone, while avoiding the serious side effects and addiction potential inherent in the use of opioids. It has been recently discovered that capsaicin, a natural product of certain species of the genus Capsicium , induces analgesia. Capsaicin (8-methyl-N-vanillyl-6Z-nonenamide) and "synthetic" capsaicin (N-vanillyl-nonanamide) are disclosed as analgesics in US-A-4,313,958, LaHann, issued February 2, 1982. Analgesic activity of capsaicin has also been discussed in the chemical and medical literature, including Yaksh, et al, Science , 206 , pp 481-483 (1979); Jancso, et al, Naunyn - Schmiedeberg's Arch . Pharmacol ., Vol. 311, pp 285-288 and Holzer et al, Eur . J . Pharm . Vol. 58, pp 511-514 (1979). US-A-4,238,505, Nelson, issued December 9, 1980, discloses 3-hydroxyacetanilide for use in producing analgesia in animals. EP-A-0089710, LaHann, et al, published September 28, 1983, describes hydroxyphenylacetamides with analgesic and anti-irritant activity. Similarly, analgesic and anti-irritant activity is disclosed for N-vanillylsulfonamides in US-A-4,401,663, Buckwalter, et al, issued August 30, 1983; N-vanillylureas in EP-A-0068590, Buckwalter, et al, published January 5, 1983; N-vanillylcarbamates in EP-A-0068592, Buckwalter, et al, published January 5, 1983; N-[(substituted phenyl)methyl]alkynlamides in US-A-4 532 139; methylene substituted N-[(substituted phenyl)methyl]-alkanamides in US-A-4 544 668; N[(substituted phenyl)methyl]-cis-monounsaturated alkenamides in US-A-4 493 848 and N-[substituted phenyl)methyl-]diunsaturated amides in US-A-4 544 669. However, none of these references suggest in any way the desirability of concurrent administration of a capsaicin derivative with a non-steroidal. Further, the art suggests that it is extremely difficult to predict when a synergistic effect will be obtained from the concurrent administration of two pharmaceutical compounds which take effect through different mechanisms. Although there are many patents which disclose analgesic and anti-inflammatory compositions containing a combination of two or more mechanistically unrelated analgesic and/or anti-inflammatory compounds, none of these compounds has a structure at all similar to that of capsaicin. See US-A-4,404,210, Schmidt, issued September 13, 1983; US-A-4,083,981, Yamamoto, issued April 11, 1978; US-A-4,315,936, Capetola et al, issued February 16, 1982; US-A-4,379,789, Capetola et al, issued April 12, 1983; and US-A-4,275,059, Flora, et al, issued June 23, 1981. Thus, based on the art, one could not have predicted that the combination of a capsaicin analog with a non-steroidal would result in a synergistic increase in analgesia. Accordingly, the present invention provides an analgesic composition comprising a safe and effective amount of a) a capsaicinoid analgesic compound of the general formula wherein R₁ is selected from OH and OCH₃, R₂ is OH, X is selected from and R is C₁₆-C₂₁ cis alkenyl; b) a non-steroidal analgesic selected from acetylsalicylic acid, diflunisal and acetaminophen and their pharmaceutically-acceptable salts; and c) a pharmaceutically-acceptable carrier; wherein the weight ratio of (a):(b) is from 3:1 to 1:3. By the term "comprising" as used herein is meant that various other inert ingredients, compatible drugs and medicaments, and steps can be employed in the compositions and methods of the present invention as long as the critical capsaicinoid/non-steroidal combination is present in the compositions and is used in the manner disclosed. The term "comprising" thus encompasses and includes the more restrictive terms "consisting essentially of" and "consisting of" which characterize the use of the compositions and methods disclosed herein. By "compatible" herein is meant that the components of the composition are capable of being commingled without interacting in a manner which would substantially decrease the analgesic efficacy of the total composition under ordinary use situations. All percentages and ratios herein are by weight unless otherwise specified. A safe and effective amount of the composition is that amount which provides analgesia, thereby alleviating or preventing the pain being treated at a reasonable benefit/risk ratio, as is intended with any medical treatment. Obviously, the amount of the composition used will vary with such factors as the particular condition that is being treated, the severity of the condition, the duration of the treatment, the physical condition of the patient, the nature of concurrent therapy (if any), the method of administration, and the specific formulation and carrier employed. By the term "capsaicin analog" or "capsaicinoid" is meant a compound of the general formula wherein R₁ is selected from OH and OCH₃, R₂ is OH, X is selected from and R is C₁₆-C₂₁ cis alkenyl. Preferred compounds include those wherein both R₁ and R₂ are OH and those wherein R₁ is OCH₃, R₂ is OH or and X is R is preferably C₁₇H₃₃. A particularly preferred capsaicinoid is N-vanillyl-9E-octadecenamide [N-vanillyloleamide]. The non-steroidal analgesic herein is selected from acetylsalicylic acid (aspirin(RTm)), diflunisal and acetaminophen. In some cases, the non-steroidals may be mixed with each other or with other drugs such as caffeine. Two popular analgesic combinations are aspirin, phenacetin and caffeine (APC) and aspirin, phenacetin and acetaminophen. Weight ratios of capsaicinoid to non-steroidal useful in the present invention range from 3:1 to 1:3. The optimum weight ratio is dependent primarily upon the relative strength of the particular capsaicinoid and non-steroidal used, and the type of severity of the pain being treated. The preferred weight ratio for the preferred combination of N-vanillyl-9E-octadecenamide and aspirin(RTm) is about 2:1. By "pharmaceutically acceptable salts" is meant those salts of the above disclosed acids which are toxicologically safe for topical or oral administration. These include the sodium, calcium, potassium, magnesium, ammonium, lysine, and arginine salts. By "pharmaceutically acceptable carrier" is meant a solid or liquid filler, diluent or encapsultaing substance which may be safely used in systemic or topical administration. Depending upon the particular route of administration, a variety of pharmaceutically-acceptable carriers, well-known in the art, may be used. These include solid or liquid fillers, diluents, hydrotropes, surface-active agents, and encapsulating substances. The amount of the carrier employed in conjunction with the capsaicinoid/opioid combination is sufficient to provide a practical quantity of material per unit dose of analgesic. Pharmaceutically-acceptable carriers for systemic administration, that may be incorporated into the compositions of this invention, include sugars, starches, cellulose and its derivatives, malt, gelatin, talc, calcium sulfate, vegetable oils, synthetic oils, polyols, alginic acid, phosphate buffer solutions, emulsifiers, isotonic saline, and pyrogen-free water. Specific pharmaceutically-acceptable carriers are described in the US-A-4,401,663, Buckwalter, et al issued August 30, 1983; EP-A-089710, LaHann, et al, published September 28, 1983; and EP-A-0068592, Buckwalter, et al, published January 5, 1983. Preferred carriers for parenteral administration include propylene glycol, ethyl oleate, pyrrolidone, aqueous ethanol, sesame oil, corn oil, and combinations thereof. Various oral dosage forms can be used, including such solid forms as tablets, capsules, granules and bulk powders. Tablets can be compressed, tablet triturates, enteric-coated, sugar-coated, film-coated or multiple compressed, containing suitable binders, lubricants, diluents, disintegrating agents, coloring agents, flavoring agents, flow-inducing agents, and melting agents. Liquid oral dosage forms include aqueous solutions, emulsions, suspensions, solutions and/or suspensions reconstituted from non-effervescent granules and effervescent preparations reconstituted from effervescent granules, containing suitable solvents, preservatives, emulsifying agents, suspending agents, diluents, sweeteners, melting agents, coloring, and flavoring agents. Preferred carriers for oral administration include ethyl oleate, methyl cellulose, gelatin, propylene glycol, cottonseed oil, sesame oil, peanut oil, corn oil, soybean oil, oil and water emulsions, and self-emulsifying oils either as free-flowing liquids or encapsulated in soft gelatin capsules. Specific examples of pharmaceutically-acceptable carriers and excipients that may be used to formulate oral dosage forms, which may be used in formulating oral dosage forms containing monoalkenamides, are described in US-A-3,903,297, Robert, issued September 2, 1975. Techniques and compositions for making solid oral dosage forms are described in Marshall, "Solid Oral Dosage Forms", Modern Pharmaceutics , Vol. 7 , (Banker and Rhodes, editors), 359-427 (1979). Specific systemic and topical formulations useful in this invention are described in the following U.S. Patent Applications, relating to specific capsaicin analogs and methods of treatment: US-A-4,401,663, Buckwalter, et al, issued August 30, 1983; EP-A-0089710; LaHann, et al, published September 28, 1983; EP-A-0068590, Buckwalter, et al, published January 5, 1983; and EP-A-0068592, Buckwalter, et al, published January 5, 1983. Topical vehicles, useful herein, are disclosed in the following U.S. Patent Applications; "Improved Penetrating Topical Pharmaceutical Compositions Combining 1-dodecylazacycloheptan-2-one", US-A-4,557,934; "Penetrating Topical Pharmaceutical Compositions Containing N-(1-hydroxyethyl)-pyrrolidone", US-A-4,537,776; and "Compounds Useful for Producing Analgesia", US-A-4,493,848. Dosages required, as well as methods of administration, are dependent on the type of non-steroidal employed, the physical condition of the patient, the severity of the pain which must be prevented or alleviated, the relative severity and importance of adverse side effects, and other factors within the judgment of the physician. The preferred method of administration in most cases will be orally. The maximum dosage of the preferred capsaicin analogue vanillyloleamide (VO) which would normally be administered orally to an average adult without unacceptable side effects is about 2000 mg (35.4 mg/kg). The minimum effective dosage is about 50 mg (0.85 mg/kg). The maximum dosage of a non-steroidal which can be administered to the average adult is also about 2000 mg (35.4 mg/kg). Thus, the maximum allowable dosage of the combination will be about 2000 mg (35.4 mg/kg). It should be noted that a sub-effective dosage of one compound may effectively potentiate the other compound; therefore, less-than-minimum dosages of each component may be utilized in some cases. Thus, when dealing with safe and effective dosage levels of the present invention, it is more appropriate to speak of safe and effective dosages of the combination rather than of the individual components. The compositions and combinations of this invention can be used to treat and prevent pain and inflammation associated with certain diseases, particularly muscular-skeletal disorders, and to provide analgesia in various disorders at the deeper structures, muscles, tendons, bursa and joints associated with disease and trauma, and in various other conditions in which capsaicinoids and/or non-steroidals have heretofore been used to alleviate pain and discomfort. The compositions of the instant invention are normally administered either topically or orally. The following non-limiting Examples illustrate the compositions of the present invention. EXAMPLE I An analgesic composition for oral administration was made using the following ingredients: N-Vanillyl-9E-octadecenamide 120 mg Aspirin(RTm) 60 mg Methylcellulose 30 mg Saline 6.0 ml The composition was prepared by dissolving the methylcellulose in the saline to yield a 0.5% solution, after which the solid aspirin(RTm) and N-vanillyl-9-octadecenamide were added and uniformly suspended in the solution by exposure to sonication. Male mice weighing approximately 25 g were orally dosed with a volume of this suspension sufficient to deliver 200 mg/kg of the octadecenamide and 100 mg/kg of the aspirin(RTm). Identical groups of mice were dosed orally with similarly prepared formulations which lacked either the aspirin(RTm), the octadecenamide, or both. Analgesic activity was demonstrated using the phenylquinone writhing test. EXAMPLE II An analgesic composition for oral administration is made using the following ingredients: N-vanillyl-9E-octadecenamide 100 g Acetylsalicylic acid 100 g Ethyl oleate 300 g The composition is made by simple dissolution of the octadecenamide in the ethyl oleate, followed by suspension of the finely divided acetylsalicylic acid in the resulting solution by vigorous mechanical blending under an inert atmosphere of argon or dry nitrogen. The creamy suspension is then loaded into soft gelatin capsules to deliver 325 mg acetylsalicylic acid and 325 mg N-vanillyl-9-octadecenamide per capsule. One such capsule is administered orally to a 60 kg human, producing analgesia. Substantially similar results are also obtained when the acetylsalicylic acid is replaced, in whole or in part, by the sodium, calcium, or lysine salts of aspirin(RTm), diflunisal, or an aspirin-phenacetin-caffeine combination (APC). EXAMPLE III A composition for oral administration is made with the following ingredients: N-vanillyl-9E-octadecenamide 225 g Aspirin(RTm) 125 g Phenacetin 83 g Caffeine 17 g Mannitol 487 g Acacia 29.3 g Starch 48.1 g Talc 15 g Calcium stearate 2 g The above ingredients are admixed in bulk and formed into tablets weighing 100 mg each using tabletting methods known in the art. Two such tablets are administered orally to a 70 kg human, producing analgesia. Effectiveness in Providing Analgesia Phenylquinone Writhing Tests The extent of analgesia obtained was determined using the phenylquinone writhing test model. Groups of eight male mice weighing between approximately 25 and 30g were dosed orally by gavage with the analgesic composition to be tested. Identical groups of mice were dosed with control compositions. Three hours after this initial administration, the mice were injected intraperitoneally with a 0.2% solution of phenylbenzoquinone in aqueous ethanol. The ability of the analgesic compositions tested to relieve the discomfort induced was measured by counting the number of abdominal contractions, or "writhes", occurring in each mouse during a 10 minute period beginning 10 minutes after injection of the phenylbenzoquinone solution. The results are expressed as a percent of the "writhing" response observed in the vehicle control group. EXAMPLE IV An analgesic composition for oral administration was made using the following ingredients: N-vanillyl-9-octadecenamide 120 mg Aspirin(RTm) 60 mg Methylcellulose 30 mg Saline 6.0 ml The composition was prepared by dissolving the methylcellulose in the saline to yield a 0.5% solution, after which the solid aspirin and N-vanillyl-9-octadecenamide were added and uniformly suspended in the solution by exposure to sonication. Male mice weighing approximately 25 g were orally dosed with a volume of this suspension sufficient to deliver 200 mg/kg of the octadecenamide and 100 mg/kg of the aspirin. Identical groups of mice were dosed orally with similarly prepared formulations which lacked either the aspirin, the octadecenamide, or both. The mouse "writhing" method for assessing pain response described above was used. The data, summarized in the following table, were normalized based on the vehicle control taken as 100. Treatment % Writhing Response Methylcellulose alone 100 Octadecenamide (200 mg/kg) 54 Aspirin(RTm) (100 mg/kg) 78 Aspirin(RTm) (100 mg/kg) + octadecenamide (200 mg/kg) 10 The response of the group given aspirin alone was not statistically distinguishable from that of the control group. The 90% inhibition of the writhing response resulting from the combination treatment (aspirin(RTm) plus octadecenamide) is greater than that expected from the sum of the aspirin treatment (22% inhibition) and octadecenamide treatment (45% inhibition) when given separately. EXAMPLE V An analgesic combination for oral administration was prepared in a manner similar to that described for Example I, the only difference being the ratio of aspirin to N-vanillyl-9-octadecenamide: N-vanillyl-9-octadecenamide 120 mg Aspirin(RTm) 120 mg Methylcellulose 30 mg Saline 6.0 ml A solution was prepared as described in Example I. The analgesic activity of the combination was assessed in mice using the "writhing" method described above. The activity of the combination was contrasted with those of similar formulations lacking the aspiring component, the octadecenamide component or both: Treatment % Writhing Response Methylcellulose alone 100 Aspirin(RTm) (200 mg/kg) 15 Octadecenamide (200 mg/kg) 33 Aspirin (200 mg/kg + octadecenamide (200 mg/kg) 1.5 The analgesic efficacy obtained from the combination is significantly greater than that from either component alone. EXAMPLE VI An analgesic composition for oral administration was made using the following ingredients: N-vanillyl-9E-octadecenamide 120 mg 3-(2',4'-diflurophenyl)-salicylic acid (diflunisal) 60 mg Ethyl oleate 6.0 ml The two analgesics were suspended in ethyl oleate with the aid of sonication and were evaluated for analgesic efficacy as described in Example X. TREATMENT % WRITHING RESPONSE Ethyl oleate alone 100 Diflunisal (100 mg/kg) 121 Octadecenamide (200 mg/kg) 50 Diflunisal (100 mg/kg) + Octadecenamide (200 mg/kg) 15 In this case, the addition of an ineffective dose of diflunisal to a moderately effective dose of octadecenamide resulted in a greatly potentiated analgesic effect. Additionally, diflunisal provides anti-inflammatory activity not possessed by the octadecenamide alone. EXAMPLE VII An analgesic composition for oral administration was made using the following ingredients: N-vanillyl-9E-octadecenamide 75 mg Acetaminophen 75 mg Ethyl oleate/benzyl alcohol (98:2 vol/vol) 5 ml The two analgesics were suspended in the ethyl oleate solution with the aid of sonication and were evaluated using the "writhing" method described above. TREATMENT % WRITHING RESPONSE Ethyl oleate solution alone 100 Acetaminophen (150 mg/kg) 127 Octadecenamide (150 mg/kg) 57 Acetaminaphen (150 mg/kg + octadecenamide (150 mg/kg) 17 In this case, the addition of an ineffective dose of acetaminophen to a marginally effective dose of octadecenamide resulted in a greatly potentiated analgesic effect. EXAMPLE VIII In order to determine the preferred capsaicinoid: non-steroidal ratios, an analgesic combination for oral administration was made using the following ingredients: 1:1 Octadecenamide:aspirin Combination N-vanillyl-9E-octadecenamide 75 mg Aspirin(RTm) 75 mg Ethyl oleate 10 ml 1:2 Octadecenamide:aspirin Combination N-vanillyl-9E-octadecenamide 50 mg Aspirin(RTm) 100 mg Ethyl oleate 10 ml 1:5 Octadecenamide:aspirin Combination (Control) N-vanillyl-9E-octadecenamide 25 mg Aspirin(RTm) 125 mg Ethyl oleate 10 ml The two analgesics were suspended in ethyl oleate with the aid of sonication and were evaluated for analgesic efficacy using the "writhing" method described above. TREATMENT % WRITHING RESPONSE Ethyl oleate alone 100 150 mg/kg aspirin(RTm) 92 150 mg/kg Octadecenamide 43 150 mg/kg Octadecenamide:Aspirin(RTm) (1:1) 48 150 mg/kg Octadecenamide:Aspirin(RTm) (1:2) 28 150 mg/kg Octadeceaamide:Aspirin(RTm) (1:5) 77 The responses of the ethyl oleate control group, the 1:5 combination control group (25 mg/kg octadecenamide + 125 mg/kg aspirin(RTm)) and the group receiving 150 mg/kg aspirin(RTm) were not significantly different. The groups receiving the octadecenamide alone and the 1:1 combination (75 mg/kg aspirin(RTm) + 75 mg/kg octadecenamide) displayed a moderate analgesic effect. The group receiving the 1:2 combination (50 mg/kg octadecenamide + 100 mg/kg aspirin(RTm)) displayed an analgesic effect unexpectedly superior to that of any of the other groups. Since the aspirin(RTm) component of this combination provides an anti-inflammatory benefit not possessed by the octadecenamide or the other capsaidin analogs, and the octadecenamide provides greater analgesia than is obtainable using aspirin alone without many of the limitative side effects of aspirin(RTm), including gastrointestinal effects, the combination clearly provides benefits not attainable using either compound alone.

Claims: An analgesic composition characterised in that it comprises a safe and effective amount of: a) a capsaicinoid analgesic compound of the general formula wherein R₁ is selected from OH and OCH₃, R₂ is OH, X is selected from and R is C₁₆-C₂₁ cis alkenyl; b) a non-steroidal analgesic selected from acetylsalicylic acid, diflunisal and acetaminophen and their pharmaceutically-acceptable salts; and c) a pharmaceutically-acceptable carrier; wherein the weight ratio of (a):(b) is from 3:1 to 1:3. A composition according to Claim 1, characterised in that R₁ and R₂ are both OH. A composition according to Claim 1, characterised in that R₁ is OCH₃, R₂ is OH, and X is A composition according to any of Claims 1 to 3 characterised in that the capsaicinoid is N-vanillyl-9-octadecenamide.

Inventors: BRAND, LARRY MILTON
Applicants: THE PROCTER & GAMBLE COMPANY
Application year: 1985
Main classification: A61K31
IPC codes: C07C271, C07C235, C07C239, A61K31, C07C301, C07C233, C07C67, A61K45, A61P25, C07C325, C07C335, C07C311, C07C275