Compositions and Methods Useful for Producing Analgesia

This invention relates to compositions, containing certain N-phenylmethylalkenamides, having analgesic activity.

While "pain" is incapable of precise definition due to its basically subjective nature, it can generally be said that the term refers to feelings of distress or suffering caused by stimulation of specialized nerve endings. A great variety of drugs have been developed to reduce pain in man and other animals; some directed to eliminating pain at its source, and others directed to blocking the assimilation of pain by the brain. Among the latter group of drugs that are designed to block the sensation of pain, are the analgesics, which generally relieve pain without causing unconsciousness. Analgesics can be further classified in two main categories: opioid analgesics, including morphine, codeine, levorphanol, and the morphine-like analgesics meperidine, and methadone; and antipyretic analgesics, such as aspirin, phenacetin, acetaminophen, phenylbutazone, and indomethacin.

Although the precise pharmacological action of these analgesics is uncertain, there are certain effects which readily distinguish the opioid analgesics from the antipyretics. In particular, the antipyretics are weak analgesics, with much of their effect in the peripheral nervous system, so that behavioral changes do not usually occur. Generally, these analgesics relieve only somatic pain originating from muscles, joints, tendons and fasciae, and are ineffective against deep visceral pain. However, the opioid analgesics are quite effective against all types of pain, with broad based action in the central nervous system. Aside from potent analgesia, the opioids, also known as narcotics, often produce effects on mood and other behavioral changes. Perhaps the most notable side effect of the opioid analgesics is the fact that their repeated use is associated with tolerance as well as psychic and physical dependence.

It has been recently discovered that capsaicin, a natural product of certain species of the genus Capsicum, induces analgesia in animals. Capsaicin (8-methyl-N-vanillyl-6E-nonenamide) and "synthetic" capsaicin (N-vanillylnonanamide) are disclosed as analgesics in U.S. Pat. No. 4,313,958, LaHann, issued Feb. 2, 1982. Analgesic activity of capsaicin has also been discussed in the chemical and medical literature, including Yaksh, et al., Science, 206, 481-483 (1979). The use of capsaicin to prevent dipilatory irritation is also disclosed in U.S. patent application Ser. No. 330,731, LaHann, et al., filed Dec. 14, 1981.

Specifically, capsaicin prevents the development of cutaneous hyperalgesia and also provides relief of deep visceral pain and severe pain. In certain tests, capsaicin produces a level of analgesia comparable to morphine, yet it is not antagonized by such narcotic antagonists as nalorphine and naloxone. Thus, capsaicin does not appear to belong to either of the major categories of analgesics, described above.

Compounds structurally similar to capsaicin have been described in the chemial literature. These references, though, do not suggest analgesic activity for these compounds. For example, Newman, "Natural and Synthetic Pepper-Flavored Substances (6)," Chemical Products, 102-106 (1954) lists the relative pungency of approximately 164 compounds, including N-vanillyloleamide and other alkenamide derivatives of capsaicin. Ott and Zimmermann, Liebigs Ann., 425, 314-337 (1921) discloses a synthesis for N-vanillyloleamide. A synthesis for N-vanillyllinoleamide is disclosed in Ferris, Australian Commonwealth, Dep. Supply, Def. Stand. Lab., No. 89 (1966) (Chem. Abs. 67:22919).

U.S. Pat. No. 4,238,505, Nelson, issued Dec. 9, 1980, discloses 3-hydroxyacetanilide for use in producing analgesia in animals. U.S. patent application Ser. No. 359,464, LaHann, et al., filed Mar. 18, 1982, describes hydroxyphenylacetamides with analgesic and anti-irritant activity. Similarly, analgesic and anti-irritant activity is disclosed for N-vanillylsulfonamides in U.S. patent application Ser. No. 360,953, Buckwalter, et al., filed Mar. 23, 1982; N-vanillylureas in U.S. patent application Ser. No. 381,672, Buckwalter, et al., filed May 25, 1982; and N-vanillylcarbamates in U.S. patent application Ser. No. 384,685, Buckwalter, et al., filed June 3, 1982.

It has now been discovered that certain N-phenylmethyl-cis-monoalkenamides have analgesic activity in humans and lower animals. In particular, these alkenamides have potent analgesic activity similar to that of capsaicin, but are substantially less toxic.

The present invention provides compositions, for producing analgesia in humans and lower animals, comprising:

(a) a safe and effective amount of a compound or pharmaceutically-acceptable salts thereof, or mixtures thereof, of the formula: ##STR1## wherein X is 0 or S, R is straight or branched cis-monounsaturated alkene having from 11 to 23 carbon atoms, R.sub.1 is H, OH, or OCH.sub.3, R.sub.2 is OH or a short-chain ester, and wherein at least one of R.sub.1 and R.sub.2 is OH or OCH.sub.3 ; and

(b) a pharmaceutically-acceptable carrier.

This invention also provides methods of producing analgesia by administering these compounds and compositions.

The compositions and methods of this invention incorporate certain N-[(substituted phenyl)methyl]-cis-monounsaturated amides (e.g., N-vanillyl-cis-monounsaturated amides), or pharmaceutically-acceptable salts thereof, (herein "monoalkenamides") of the formula: ##STR2## wherein X is O or S; R is straight or branched, cis-monounsaturated alkene having from 11 to 23 carbon atoms; R.sub.1 is H, OH or OCH.sub.3 ; R.sub.2 is OH or a short-chain ester; and wherein at least one of R.sub.1 and R.sub.2 is OH or OCH.sub.3. R preferably contains from 16 to 21 carbon atoms and, preferably, the unsaturated bond is at position six or greater, i.e., wherein R is a (nZ-alkene), n is at least six. Also preferred are monoalkenamides wherein X is O, monoalkenamides wherein R.sub.1 is OCH.sub.3 and R.sub.2 is OH, and monoalkenamides wherein R.sub.2 is a short-chain (i.e., C.sub.1 -C.sub.6) ester, e.g., acetoxy.

It has been found that the "cis" (or "Z") monounsaturated alkenamides have analgesic activity significantly greater than that of their "trans" (or "E") isomers. The "cis" prefix is used in designating geometrical isomers in which there is a double bond between two carbon atoms and wherein the primary substituent group for each of the two carbon atoms is on the same side of the double bond axis. (Conversely, the "trans" isomer designates a spatial arrangement wherein the primary substituent groups on each of the two carbon atoms in the double bond are on the opposite sides of the double bond axis.)

Preferred monoalkenamides include those wherein R is derived from such cis-monounsaturated fatty acids as 9Z-tetradecenoic (myristoleic) acid, 9Z-hexadecenoic (palmitoleic) acid, 9Z-octadecenoic (oleic) acid, 6Z-octadecenoic (petroselinic) acid, 11Z-octadecenoic acid, 10Z-nonadecenoic acid, and 13Z-docosenoic (erucic) acid. Particularly preferred monoalkenamides include N-vanillyl-9Z-octadecenamide (N-vanillyloleamide) and N-[(4-acetoxy-3-methoxyphenyl)methyl]-9Z-octadecenamide. Preferred pharmaceutically-acceptable monoalkenamide salts include the sodium, potassium, calcium, magnesium, and ammonium salts.

The monoalkenamides described herein can be readily prepared by the following general synthetic scheme: ##STR3## The fatty acids used in the synthesis of preferred monoalkenamides are commercially-available.

The compositions of the present invention comprise:

(a) a safe and effective amount of a monoalkenamide; and

(b) a pharmaceutically-acceptable carrier.

A safe and effective amount of monoalkenamide 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 monoalkenamide 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 specific formulation and carrier employed, and the solubility and concentration of monoalkenamide therein.

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 monoalkenamide 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 composition 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 following U.S. patent applications, all incorporated by reference herein: Ser. No. 359,464, LaHann, et al., filed Mar. 18, 1982; Ser. No. 360,953, Buckwalter, et al., filed Mar. 23, 1982; Ser. No. 381,672, Buckwalter, et al., filed May 25, 1982; and Ser. No. 384,685, Buckwalter, et al., filed June 3, 1982. Preferred carriers for parenteral administration include propylene glycol, ethyl oleate, pyrrolidone, ethanol, and sesame oil. Preferably, the pharmaceutically-acceptable carrier, in compositions for parenteral administration, comprises at least about 90% by weight of the total composition.

Various oral dosage forms can be used, including such solid forms as tablets, capsules, granules and bulk powders. These oral forms comprise a safe and effective amount, usually at least about 5%, and preferably from about 25% to about 50% of the monoalkenamide. 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 gelatin, propylene glycol, cottonseed oil and sesame oil. 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 U.S. Pat. No. 3,903,297, Robert, issued Sept. 2, 1975, incorporated by reference herein. 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), incorporated by reference herein.

The compositions of the present invention can also be administered topically to a biologic subject, i.e., by the direct laying on or spreading of the composition on epidermal or epithelial tissue. Such compositions include lotions, creams, solutions, gels and solids. These topical compositions comprise a safe and effective amount, usually at least about 0.5%, and preferably from about 1% to about 2%, of the monoalkenamide. Suitable carriers for topical administration of the monoalkenamide preferably remain in place on the skin as a continuous film and resist being washed off easily be perspiration or by immersion in water. Generally, the carrier is organic in nature and capable of having dispersed or dissolved therein the monoalkenamide. The carrier may include pharmaceutically-acceptable emollients, emulsifiers, thickening agents, and solvents.

Specific systemic and topical formulations useful in this invention are described in the following U.S. patent applications, all incorporated by reference herein: Ser. No. 359,464, LaHann, et al., filed Mar. 18, 1982; Ser. No. 360,953, Buckwalter, et al., filed Mar. 23, 1982; Ser. No. 381,672, Buckwalter, et al., filed May 25, 1982; and Ser. No. 384,685, Buckwalter, et al., filed June 3, 1982. Topical vehicles, useful herein, are disclosed in the following U.S. patent applications, incorporated by reference herein: "Improved Penetrating Topical Pharmaceutical Compositions Combining 1-dodecylazacycloheptan-2-one", Ser. No. 506,275, Cooper, filed June 21, 1983; and "Penetrating Topical Pharmaceutical Compositions Containing N-(2-hydroxyethyl)-pyrrolidone", Ser. No. 506,273, Cooper, filed June 21, 1983. Additional formulations, useful for parenteral, oral, and topical administration of monoalkenamides, are disclosed in the following U.S. patent applications concurrently filed herewith, all incorporated by reference herein: "Novel Compounds and Compositions Useful for Producing Analgesia", Ser. No. 514,207, LaHann, Janusz, and Buckwalter; "Novel Compounds and Compositions Useful for Producing Analgesia" , Ser. No. 514,204, Janusz and LaHann; and "Novel Compounds and Compositions Useful for Producing Analgesia", Ser. No. 514,205, Janusz, Buckwalter and LaHann.

The present invention also encompasses methods of producing analgesia in humans or lower animals through administering, to the human or lower animal, a safe and effective amount, usually from about 1 mg to about 3600 mg per day, preferably from about 200 mg to about 2000 mg per day, of a monoalkenamide. While dosages higher than the foregoing are effective to produce analgesia, care must be taken in some individuals to prevent adverse side effects. The monoalkenamides and compositions of this invention can be used to treat and prevent pain, 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 compounds such as aspirin, codeine, and morphine have heretofore been used to alleviate pain and discomfort.

The monoalkenamides and compositions of the instant invention can be administered topically or systemically. Systemic application includes any method of introducing the monoalkenamide into the tissues of the body, e.g., intrathecal, epidural, intramuscular, transdermal, intravenous, intraperitoneal, subcutaneous, sublingual, and oral administration.

A preferred method of parenteral administration is through intramuscular injection. As is known and practiced in the art, all formulations for parenteral administration must be sterile. For mammals, especially humans, (assuming an approximate body weight of 70 kg) individual doses of from about 2 mg to about 400 mg of monoalkenamide are acceptable. Individual doses of from about 50 mg to about 200 mg are preferred.

A preferred method of systemic application of the monoalkenamides is through oral administration. For mammals, especially humans, (assuming an approximate body weight of 70 kg) individual doses of from about 1 mg to about 900 mg of monoalkenamide are acceptable. Individual doses of from about 50 mg to about 600 mg are especially preferred.

Topical administration can be used to produce local or systemic analgesia, through directly laying on or spreading a safe and effective amount of the monoalkenamide, or composition containing a monoalkenamide, on epidermal or epithelial tissue, including outer skin and oral, gingival, and nasal tissue. The amount of monoalkenamide to be topically administered depends upon such factors as the sensitivity, type and location of tissue to be treated, the composition and carrier (if any) to be administered, and the particular monoalkenamide to be administered as well as the particular disorder to be treated and the extent to which systemic (as distinguished from local) analgesic effects are desired. The extent of systemic analgesia also depends upon such factors as the amount of monoalkenamide, the area of tissue to be covered, and the ability of the monoalkenamide composition to penetrate the skin tissues.

The following non-limiting Examples illustrate the compositions, processes, and uses of the present invention.

N-vanillyl-9Z-octadecenamide (N-vanillyloleamide) was synthesized by the following method: ##STR4## Specifically, 3.15 g of 4-hydroxy-3-methoxybenzylamine-HCl was suspended in 25 ml of N,N-dimethylformamide (DMF), and stirred. Added were 6.6 ml of a 5N solution of NaOH, and the mixture was stirred for an additional 10 to 15 minutes. The DMF mixture was chilled in an ice bath, and 5 g of 9Z-octadecenyl chloride (oleoylchloride), dissolved in chloroform, was added dropwise. The mixture was then stirred for 3 hours, allowing it to come to room temperature. The mixture was then poured into 300 ml water, layers separated, and the aqueous layer extracted with ethyl ether. The extracts were washed with HCl, sodium bicarbonate, water, and brine, and then dried and filtered. 7.63 g of crude N-vanillyl-9Z-octadecenamide was obtained. Purification by chromatography (silica gel with 40% ethyl acetate/hexane) and recrystallization from methanol and water gave 5.9 g of analytically pure product. Its structure was confirmed via nuclear magnetic resonance and infrared spectroscopy.

In the above example, 9Z-tetradecenyl chloride, 6Z-octadecenyl chloride, 11Z-octadecenyl chloride, 10Z-nonadecenyl chloride, 13Z-docosenyl chloride, and 9Z-hexadecenyl chloride are substituted for 9Z-octadecenyl chloride, respectively, thereby obtaining each respective N-vanillyl-alkenamide.

An analgesic composition, according to the present invention, was made comprising:

The composition was made by simple dissolution of the monoalkenamide in the liquid solvents. A mouse weighing 30 g, was injected subcutaneously with 0.2 ml of the composition, producing analgesia.

A composition, according to the instant invention, for parenteral administration, is made with the following ingredients:

The monoalkenamide is dissolved in the carrier and a human subject, weighing 70 kg, is injected subcutaneously with 1.0 ml of the composition thereby prepared, producing analgesia. At eight-hour intervals, two more subcutaneous injections are made, of 1.0 ml of the composition per administration, for a total of 300 mg N-vanillyl-10 Z-nonadecenamide administered over a twenty-four hour period.

In the above example, N-vanillyl-9Z-tetradecenamide, N-vanillyl-6Z-octadecenamide, N-vanillyl-11Z-octadecenamide, 9-methyl-N-vanillyl-9Z-octadecenamide, and 9-ethyl-N-vanillyl-9Z-octadecenamide are substituted, respectively, for N-vanillyl-10Z-nonadecenamide, with substantially similar results.

A composition, according to the instant invention, for parenteral administration, is made with the following components:

A human subject, weighing 70 kg, is injected via deep-intramuscular injection, with 1.0 ml of the composition prepared above, producing analgesia.

In the above example, N-vanillyl-10Z-nonadecenamide, N-vanillyl-9Z-dodecenamide, N-vanillyl-13Z-docosenamide, 12-hydroxy-N-vanillyl-9Z-octadecenamide, N-vanillyl-9Z-octadecethioamide, and N-[(3,4-dihydroxyphenyl)methyl]-9Z-octadecenamide are substituted, respectively, for N-vanillyl-9Z-octadecenamide, with substantially similar results.

A composition, according to the instant invention, for parenteral administration, is made with the following components:

The above ingredients are admixed, forming a suspension. A human subject, weighing approximately 70 kg, is injected, via intramuscular injection, with 2.0 ml of the composition formed above, producing analgesia.

A composition, according to the instant invention, for parenteral administration, is made by admixing the following components:

A human subject, weighing 70 kg, is injected via intramuscular injection, with 2.0 ml of the composition prepared above, producing analgesia.

In the above example, N-[(4-butoxy-3-methoxyphenyl)methyl]-9Z-octadecenamide and N-[(4propioxy-3-methoxyphenyl)methyl]-11Z-octadecenamide are substituted, respectively, for N-[(4-acetoxy-3-methoxyphenyl)methyl]-9Z-octadecenamide, with substantially similar results.

A composition, according to the instant invention, was made with the following components:

The monoalkenamide was dissolved in the sesame oil carrier and the solution thus obtained was administered orally to a rat, weighing 100 g, (resulting in a dose of 200 mg per kg) producing analgesia.

A composition, according to the instant invention, for oral administration, is made with the following components:

5.0 ml of the syrup thereby prepared is administered orally to a human subject, producing analgesia.

In the above example, flavoring agents, sweetening agents such as sucrose, lactose, mannitol and saccharin, and preservatives such as glycerin, methyl paraben, propylparaben, benzoic acid, sodium benzoate and alcohol, are added, singly or in combination, to the composition formed above, with substantially similar results.

A composition, according to the instant invention, for oral administration, is made with the following components:

Soft gelatin capsules, each having a volume of 0.3 ml, are filled with the composition formed above. Two capsules are administered to a human subject every eight hours, producing sustained analgesic effects.

A composition, according to the instant invention, for oral administration, is made with the following components:

The above ingredients are admixed into a bulk mixture, totalling 100 g. Compressed tablets are formed, using tabletting methods known in the art, each containing 0.5 g of the bulk mixture. A human subject, weighing approximately 70 kg, is orally administered two of the tablets, for a total dose of 700 mg of monoalkenamide, producing analgesia.

A composition, according to the instant invention, for oral administration, is made with the following components:

The above ingredients are admixed into a bulk mixture totalling 217.4 g. Chewable tablets are formed, using tabletting methods known in the art, each containing 1.09 g of the bulk mixture, for a total of 200 tablets formed. A human subject, weighing approximately 70 kg, is orally administered three of the tablets, for a total dose of 1500 mg of monoalkenamide, producing analgesia.

A composition, according to the instant invention, for oral administration, is made with the following components:

A capsule is made by filling with the above ingredients, and administered to a human subject, weighing approximately 70 kg, producing analgesia.

A lotion composition, according to the instant invention, for topical administration, is formed through admixing the following components (percentages-by-weight):

Approximately 4 ml of the lotion formed is applied to a 80 cm.sup.2 portion of the skin of a human subject, producing analgesia.

In the above example, N-vanillyl-9Z-octadecenamide is substituted for N-vanillyl-6Z-octadecenamide, with substantially similar results.

An ointment composition, according to the instant invention, for topical administration, is formed with the following components (percentages-by-weight):

The components are admixed and approximately 6 ml of the ointment is applied to a 100 cm.sup.2 portion of the skin of a human subject, producing analgesia.

Five compositions were prepared, each containing an equimolar quantity of a monoalkenamide or other alkenamide. The alkenamides incorporated into each composition were as follows:

Compositions were formulated so that equal volumes of carrier contained equimolar amounts of alkenamide. For example, the specific formulation of Composition A was:

The degree of thermal analgesia induced by each of Compositions A through E was determined by the "mouse hot plate test" (MHP). An additional composition, F, containing no alkenamide, was tested as a vehicle control. The MHP system is designed to detect and evaluate agents which elevate the threshold for the perception of pain. Classically, this method has been utilized primarily to evaluate opioid (narcotic) analgesic agents, such as morphine. Unless administered in toxic quantities, antipyretic analgesics, such as aspirin or acetaminophen, exhibit little or no activity in the MHP system.

Groups of 10 male CF-1 mice were used to evaluate each alkenamide composition. The test procedure consisted of placing a particular mouse on a surface heated to 55.degree. C. and observing its behavior. The point in time at which the mouse either rapidly fanned or licked one of its paws was noted, and the total elapsed time from the first contact with the heated surface was determined (herein "response time"). If the response time for a particular mouse reached sixty seconds, the mouse was removed from the hot plate so as to prevent organic damage, and the response time recorded as sixty seconds. Hence, the maximum measurable response time for any particular composition was sixty seconds.

For each mouse in a group, the pre-drug response time was determined, i.e., before administration of the test composition. The pre-drug response times were averaged for each mouse in the group, ranging from 4.7 to 5.3 seconds.

The MHP test was repeated 3 hours after each mouse in a group was injected subcutaneously with 0.2 ml of the compositions to be evaluated, resulting in a total dose of 0.68 millimoles of alkenamide per kilogram weight for each mouse. These post-drug response times were noted and are set forth in Table 1, below for each composition tested.

The data in Table 1 demonstrate that the monoalkenamides of the present invention, e.g., N-vanillyl-9Z-octadecenamide and N-vanillyl-6Z-octadecenamide, have significantly higher analgesic activity than their trans-monounsaturated alkenamide isomers.