SALICYLIC ACID AND THE SALIC YLATES.
Salicylic acid (ortho-oxy-benzoic acid; acidum salicylicum, U. S. P.) is an or ganic acid existing naturally in the oils of wintergreen (Gaultheria procumbens) and sweet-birch (Betula lenta) in com bination as methyl-salicylate; its arti ficial preparation was discovered by Kolbe in 1874, who produced it from carbolic acid, caustic soda, and carbonic acid gas by the aid of moderate heat, and subsequent treatment with hydro chloric acid. Salicylic acid occurs as a light, fine, white, crystalline powder or as small needles, having no odor and a sweet taste, with acrid after-taste. It is soluble in 2 parts of ether, 2.4 parts of alcohol, 60 parts of cold and 16 parts of warm glycerin, in SO parts of chloro form, in 14 parts of hot or 450 parts of cold water, in 2 parts of olive-oil (by aid of heat), and in 30 parts of sweet spirit of nitre. Its solubility is increased by addition of the phosphates, citrates, and acetates of the alkalies and borax. Pure salicylic acid should be free from color and from the odor of phenol, and when heated on platinum foil it should leave no ash.
Preparations and Doses. — Acidum salicylicum (U. S. P.), 10 to 30 grains.
Lithii salicylas (U. S. P.), 10 to 30 grains.
Methyl salicylas, U. S. P. (artificial or synthetic oil of wintergreen), 1 to 10 minims.
Phenyl salicylas (salol, U. S. P.), 3 to 15 grains.
Physostigminw salicylas, U. S. P. (eserine salicylate), to grain.
Sodii salicylas (U. S. P.), 8 to GO grains.
Administration.—Salicylic acid should not be administered in pill, powder, or capsule, but always in solution, as it is very irritating to mucous surfaces. It is preferably given with ammonium or potassium acetate, potassium citrate, or ammonium phosphate, all of which in crease its solubility in water, or it may be given in some syrup, flavored with compound spirit of lavender, or in elixir of orange. H. C. Wood suggests an extemporaneous solution of ammonium salicylate made by mixing 1 drachm of salicylic acid and 5 drachms of syrup, adding aqua ammoniac in sufficient quan tity to dissolve the acid, which yields a finished product of about 6 drachms, one teaspoonful representing about 10 grains of the acid. A similar result may be obtained by administering the acid (10 to 15 grains) in a tablespoonful of spirit of Mindererus (liquor ammonii acetatis, U. S. P.). The sodium salicylate (con taining SO per cent. of salicylic acid) or lithium salicylate may be given in a strongly-aromatized syrup. Methyl-salic ylate, or artificial oil of wintergreen, or the natural oil of wintergreen may be given in emulsion or in capsule. The tinnitus caused by salicylic acid may be relieved by a 20-grain dose of bromide of sodium. Physostigmine salicylate is not used for the same purposes as the other official salicylates, and will be found under PIIYSOSTIGMA.
Salicylic acid should not be combined with exalgin, as a reaction takes place between them.
Contra-indications.—The use of sali cylic acid and the salicylates is contra indicated in middle-ear disease, inflam mation or congestion of the brain or meninges, albuminuria, and renal disease with impaired function, as in pregnancy and Bright's disease.
Physiological Action.—Salicylic acid has an irritant action upon the mucous membranes. When given to man in medicinal doses it produces symptoms simulating cinchonism: a feeling of full ness in the head, tinnitus aurium, and, perhaps, slight giddiness. Larger doses may give rise to headaches, partial deaf ness, mydriasis, amblyopia, or partial blindness. Moderate doses do not seem to affect the respiration or circulation very much. The respiration is somewhat quickened, owing to an irritation of the pulmonary vagi and probably some stim ulation of the respiratory centres; after very large doses failure of respiration occurs through a gradual or sudden depression or paralysis of the centres (Wood). Moderate doses seem to increase arterial pressure slightly by exciting the vasomotor centres and directly increase the cardiac force. Very large doses cause a fall of arterial pressure, due, in part, to direct action upon the heart. The action of salicylic acid upon the nervous system appears to be a depression of the motor nervous centres, full doses caus ing, in addition to the head-symptoms noted above, a diminution of the reflexes and, in large doses, epileptiform convul sions by direct action upon the brain. The action of salicylic acid in medicinal doses upon the normal temperature is variable and slight; if fever be present, its lowering action upon the fever is marked. This latter effect is supposed to be produced by inhibiting heat-produc tion and increasing heat-dissipation, but our knowledge upon this point is far from certain. The first effect of an antipyretic dose in fever is profuse sweating, which may appear within fifteen minutes. Very scan the temperature begins to fall, the depression reaching its maximum in about six hours (Justi). Wood believes that the perspiration can scarcely be the only factor in the reduction of tempera ture, as there appears to be no relation between its amount and the degree of the fall, and it usually ceases before the latter reaches its maximum. Salicylic acid is absorbed and circulates in the blood, probably, as sodium salicylate, and is eliminated chiefly through the kidneys, partly unchanged and partly as salic yluric acid, the green discoloration of the urine being due to indican or pyro catechin. The salicylates increase the elimination of urea and uric acid (Haig). Large doses of salicylic acid produce an irritant effect upon the kidneys. The action of salicylic acid and its salts ap pears to be identical.