Abstract:
Alkali and alkaline earth metal salts of salicylamide are administered in solid oral dosage forms with substantially improved analgesic, anti-inflammatory, antipyretic and sedative results as compared with salicylamide. Highest blood levels are obtained by administering enteric-coated salicylamide salt dosage forms.

Description:
This is a continuation of application Ser. No. 255,901, filed May 22, 1972 now abandoned, in turn a continuation of Ser. No. 22,049 filed Mar. 23, 1970 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to orally administratable dosage units for use as an analgesic, antipyretic, anti-inflammatory, or sedative. 
     Salicylamide is widely used in analgesic, anti-inflammatory, and antipyretic preparations. There are many conflicting reports, however, as to the efficacy of this drug. Salicylamide is a relatively insoluble drug, having a water solubility of only 0.2 percent at 30°C. When orally administered from tablets or capsules, a substantial amount of salicylamide fails to dissolve during passage through the gastrointestinal tract and can be recovered in the feces. Often as much as one-third of the drug is lost in this manner. 
     Additionally, a significant portion of the salicylamide which does go into solution is conjugated during absorption through the intestinal walls to its glucuronide and sulfate derivatives, neither of which has the desired pharmacological activity. Thus, very little of the salicylamide orally administered in solid dosage forms reaches the blood stream in active form. 
     When administered intravenously, salicylamide elicits excellent analgesic, anti-inflammatory, antipyretic and sedative responses. The relative strength of these responses is dose dependent. Because intravenous administration is impractical for most conditions of use, a need remains for a means of orally administering effective amounts of salicylamide. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of this invention to provide a solid oral dosage form for use as an analgesic, anti-inflammatory, antipyretic, or sedative. 
     Another object of this invention is to provide a solid oral dosage form for effectively administering salicylamide. 
     In accomplishing these objects, one feature of this invention resides in an orally administratable dosage unit for use as an analgesic, antipyretic, anti-inflammatory, or sedative comprising a unit dosage amount of an alkali or alkaline earth metal salt of salicylamide in an orally acceptable solid pharmaceutical carrier. 
     Another feature of this invention resides in a dosage unit, as described above, having an enteric coating that resists solution in gastric fluid but disintegrates in the small intestine. 
     Other objects, features and advantages of this invention will become more apparent to those skilled in the art from the detailed description of the invention which follows. 
    
    
     DESCRIPTION OF THE INVENTION 
     In accordance with this invention, it has been found that oral administration of alkali and alkaline earth metal salts of salicylamide from solid dosage forms provides therapeutically effective blood levels of salicylamide, substantially higher than when salicylamide itself is administered. Dosage forms containing these salicylamide salts have greater usefulness as analgesics, antipyretics, anti-inflammatories, and sedatives than do similar dosage forms containing salicylamide. 
     Salts useful in the present invention can be represented by the formula: ##SPC1## 
     wherein Me is an alkali or alkaline earth metal cation of valence n and n is 1 or 2. 
     Various pharmaceutically acceptable alkali and alkaline earth metal salts of salicylamide can be orally administered. Of these, the sodium, potassium, magnesium and calcium salts are preferred. Best results are obtained with the sodium salt. 
     Two major problems with oral salicylamide administration, namely, insolubility and conjugation during absorption, have long been recognized. Both are improved upon by the present invention. Thus, alkali and alkaline earth metal salts of salicylamide dissolve substantially completely in the gastro-intestinal tract and are available for absorption, eliminating the problem of the drug simply passing through the gastro-intestinal tract. And, significantly, the greater availability of the drug to the wall of the small intestine can overcome the problem of inactivation by conjugation during absorption. This is especially true when the dosage unit is provided with an enteric coating that resists solution in gastric fluids but disintegrates in the small intestine. Through use of an enteric coating, the highly soluble salicylamide salt is presented to a relatively small area of the intestinal wall in high concentration. By presenting a quantity of drug higher than that which can be conjugated by the means available, the bulk of the salicylamide salt is absorbed in a free state. Thus, the large quantity of salicylamide salt presented to a small segment of the small intestine wall tends to overwhelm or swamp the inactivation mechanism. 
     Salicylamide salts can be effectively administered from various solid oral dosage forms, such as tablets, pills, powders, or capsules. These dosage forms can contain conventional additives such as diluents, binders, lubricants, disintegrators, and coloring agents. Typical diluents include dicalcium phosphate, calcium sulfate, lactose, kaolin, mannitol, dry starch, and powdered sugar. Typical binders include starch, gelatin, sugars such as sucrose, molasses, and lactose, natural and synthetic gums such as acacia, sodium alginate, extract of Irish moss, carboxymethylcellulose, methylcellulose, and polyvinylpyrrolidone, polyethylene glycol, ethylcellulose, and waxes. Typical lubricants for use in these dosage forms include boric acid, sodium benzoate, sodium acetate, sodium chloride, leucine, and polyethylene glycol. Disintegrators which can be present include such agents as starch, methylcellulose, agar, bentonite, cellulose and wood products, alginic acid, guar gum, citrus pulp carboxymethylcellulose, and sodium lauryl sulfate. If desired, conventional pharmaceutically acceptable dyes can be incorporated in the dosage unit. 
     Best results are obtained when the oral dosage unit has an enteric coating. Any enteric coating can be employed so long as it will protect the salicylamide salt from dissolution as it passes through the stomach and disintegrate in the small intestine. Usually, the enteric coating material is a cellulose lower fatty acid phthalate, particularly cellulose acetate phthalate. However, other cellulose derivatives can be used. For example, cellulose ethers or mixed ether esters can be substituted for the cellulose esters. Thus, among the enteric coating materials which can be used are the materials formed by reacting cellulose acetate, cellulose propionate, cellulose acetate butyrate, ethyl cellulose, butylcellulose, etc., with phthalic or maleic anhydrides or the like in the presence of a tertiary organic base. The only limitation on the enteric coating is that it shall preserve the salicylamide salt from dissolution until it reaches the small intestine. Therefore, in addition to the coatings described above, one can use any of the conventional enteric coatings such as shellac and others described in Remington&#39;s &#34;Pharmaceutical Sciences&#34;, Thirteenth Edition, Mach Publishing Company, 1965, pp 604-605. 
     The solid oral dosage form, whether tablets, capsules, pills or powders, is prepared in the conventional manner. When an enteric coating is used, the dosage form can be dipped, sprayed, etc., with the coating material until a coating of the desired thickness is obtained. Those skilled in the art are well aware of the standard techniques which can be used to prepare these dosage forms and to provide them with an enteric coating. 
     Salicylamide salts are administered in the same unit dose amounts conventionally used with salicylamide. In general each dosage contains from 50 to 750 milligrams of the salcylamide salt. Typically, about 300 milligrams are incorporated in the dosage unit. 
     Salicylamide salts can be administered in conjunction with other drugs to obtain enhanced efficacy. When this is done, the amount of the salicylamide salt in the dosage unit can vary from the ranges previously set forth and the amount to be administered can be readily determined by those skilled in the art. Typical of other drugs that can be combined with the alkali and alkaline earth metal salts of salicylamide to provide a combination dosage unit are: phenacetin, aspirin, sodium salicylate, caffeine, acetaminophen, scopolamine, phenylephrine hydrochloride, glycerol guaiacolate, chlorpheniramine maleate, belladonna alkaloids, dextromethorphan hydrobromide, ephidrine hydrochloride, and phenylpropanolamine hydrochloride. 
     Unexpectedly good results are obtained when a salicylamide salt is combined with an alkali or alkaline earth metal salt of acetominophen having the formula: ##SPC2## 
     wherein Me is an alkali or alkaline earth metal cation of valence n and n is 1 or 2. Such dosage forms, containing salts of both drugs, are prepared in a conventional manner, as described above. The mole ratio of the salicylamide salt to the acetominophen salt can vary in the range of 0.25:1 to 4:1 but the total unit dosage amount of drug should be from 50 to 750 milligrams. Though one can depart from these ranges, the synergistic effect, resulting in higher blood levels of drug, is not present. These combination dosage forms too benefit from enteric coating. 
     In a specific example of the invention, sodium salicylamide was prepared by incrementally adding salicylamide (10 grams, 0.073 mole) to 1 Normal sodium hydroxide (70 milliliters, 70 milliequivalents) and stirring the mixture for 1 hour. Thereafter, the reaction product was extracted with chloroform and ether to remove excess salicylamide. Water was removed from the aqueous layer by spin evaporation under vacuum, depositing the sodium salicylamide product. The solid product was purified by dissolving in methyl alcohol containing anhydrous sodium sulfate. The methyl alcohol solution was filtered and spin evaporated in vacuo leaving the purified white solid sodium salicylamide product. 
     Other alkali and alkaline earth metal salts of salicylamide can be prepared in a similar manner. 
     To compare the dissolution rates of sodium salicylamide and salicylamide, 300 milligram half-inch diameter tablets having a thickness of 1 millimeter, were prepared in a Carver Press at 10 pounds per square inch pressure. When placed in simulated gastric fluid (400 milliliters, 0.1 Normal HCl) at 37°C in a round bottom flask magnetically stirred at 60 RPM, the results set forth in the following table were obtained. 
     
         ______________________________________    PERCENT DISSOLVEDELAPSED    SODIUMTIME       SALICYLAMIDE SALICYLAMIDE______________________________________1       min.   16             &lt;12       min.   34             &lt;15       min.   68             111      min.   97             120      min.   100            21       hr.    --             52       hr.    --             184       hr.    --             328       hr.    --             5420      hr.    --             8840      hr.    --             9744      hr.    --             100______________________________________ 
    
     When tablets prepared in an identical manner were tested under the same conditions in simulated intestinal fluid (6.80 parts monobasic potassium phosphate, 1.52 parts sodium hydroxide, 1000 parts distilled water) of pH 7.5, the following results were obtained. 
     
         ______________________________________  PERCENT DISSOLVEDELAPSED TIME    SODIUM SALICYLAMIDE                      SALICYLAMIDE______________________________________ 1 Min.  15.0              -- 5 min.  78.5              --10 min.  96.8              --15 min.  98.5              --20 min.  100               --25 min.  --                --30 min.  --                6.2 4 hr. 35 min.    --                33.417 hr.  5 min.    --                89.524 hr. 10 min.    --                93.026 hr. 25 min.    --                96.546 hr. 30 min.    --                100.0______________________________________ 
    
     Conventionally prepared tablets containing alkali and alkaline earth metal salts of salicylamide provide substantially higher blood levels, in mammals, of salicylamide than do identical tablets containing salicylamide itself. Thus, this invention provides solid dosage forms with significantly improved usefulness as analgesics, antipyretics, anti-inflammatories, and sedatives. 
     While the invention has been described and pointed out with reference to certain preferred embodiments thereof, those skilled in the art will appreciate that various changes and modifications and substitutions can be made without departing from the spirit of the invention. It is intended, therefore, that the invention be limited only by the scope of the claims which follow.