This section is from the book "A Text-Book Of Pharmacology, Therapeutics And Materia Medica", by T. Lauder Brunton. Also available from Amazon: A text-book of pharmacology, therapeutics and materia medica.
1 Bull, de Therap., Jan. 30, 1883; Centralblt. f. d. med. Wissenschaft, No. 42, 1883.
A crystalline acid obtained by the combination of the elements of carbolic acid with those of carbonic acid gas and subsequent purification, or from natural salicylates such as the oils of winter-green (Gaultheria procumbens, Linn.) and sweet birch (Betula lenta, Linn.).
Characters. - In white acicular crystals, inodorous but light and easily diffused and then irritating to the nostrils; taste at first sweetish, then acid.
The crystals melt at about 311° F. (155° C), and below 392° F. (200° C.) volatilise without decomposition.
Solubility. - It is soluble in 500 to 700 parts of water at ordinary temperatures; readily soluble in alcohol, ether, and hot water; soluble also in solutions of citrate or acetate of ammonium, phosphate of sodium, or borax.
Reactions. - The aqueous solution gives with solution of perchloride of iron a reddish-violet colour. An alcoholic solution allowed to evaporate spontaneously should leave a perfectly white residue.
Dose. - 5 to 30 grains.
Unguentum Acidi Salicylici (salicylic acid, 1; soft paraffin, 18; hard paraffin 9).
Action. - When mixed in a proportion of 1 to 10 per cent. with fluids containing the germs of bacteria it will prevent their development, and in the proportion of 1 in 60 will destroy bacteria when swarming in a fluid (p. 91). Salicylic acid likewise destroys the life of the torula, and prevents alcoholic fermentation, as well as the fermentation caused by the organic ferments, etc. (p. 78).
It has little power to reduce the temperature in health, but is a most powerful agent in lowering the temperature of fever. When injected into the blood, or administered by the stomach in large quantities, it lowers the pulse-rate, blood-pressure, and respiration. When taken in medicinal doses for some time, it produces noises in the ears, deafness, giddiness, and headache, in this respect resembling quinine. Occasionally it has caused sudden depression of the circulation and collapse.
In large doses salicylic acid causes feeble circulation, lowers the blood-pressure, and produces death through paralysis of the respiration. It is excreted in the perspiration, saliva, and urine. During its excretion it frequently irritates the kidneys and produces albuminuria. It appears in the urine partly as salts of salicylic acid, and partly in combination with glycol as salicyluric acid. After its use the urine is not unfrequently brown by reflected and green by transmitted light, and contains a substance which reduces copper solution.
Uses. - Externally it has been employed as an antiseptic instead of carbolic acid, and has been used by insufflation in diphtheria successfully. A mixture of 2 parts with 100 of tallow applied directly to the feet, not to the stockings, has been found most useful in preventing sweating and soreness of the feet in soldiers after a long march. In intertrigo 1 to 2 per cent. in starch soothes the irritation and prevents decomposition of the sweat. A lotion (4 per cent.) is useful in pruritus and chronic urticaria, and one of half per cent. in alopecia furfuracea. It has been recommended for soft sores, which should be kept covered with the pure acid for two days, and then treated with emollient ointment. Salicylic acid dissolved in collodion flexile (gr. xxx. to 3j.) is very useful for corns and warts, and in a plaster with gutta-percha in corns, tylosis, and in the thickened patches of chronic eczema; also to hasten the peeling of the palms and soles after scarlet fever.
In doses of 3 to 5 grains taken during meals it is very useful in arresting fermentative changes in the stomach and preventing acidity and flatulence. It is usually employed internally in the form of salicylate of sodium (p. 628). As already mentioned it is useful both in acute and chronic rheumatism. It is of much less use in typhoid fever than in rheumatism, and, although it has some antiperiodic action, it is not such a powerful remedy in malarious affections as quinine. Salicylate of sodium is useful in phlegmasia alba. As already mentioned, it relieves headache. It seems to have a peculiar power of increasing the secretion of bile and rendering it more watery. In this it differs from most other cholagogues, which increase the proportion of solids in the bile. It is therefore indicated in cases where there is a tendency to the formation of gall-stones.
Characters. - Colourless micaceous crystals with a peculiar smell.
Solubility. - Insoluble in water, dilute acids or alkalis. Sparingly soluble in cold alcohol, more readily in hot alcohol.
Purification. - As the commercial naphthalin is often impure it should be purified by washing it with alcohol on a filter until the alcohol is colourless, then drying and subliming.
Dose. - For adults 11/2 - 8 grains as a single dose. As much as 80 grains may be given during the day. For children, 1 1/2-3 grains every three hours.
Administration. - In the form of powder mixed with sugar and scented with oil of bergamot it may be taken in wafers or capsules. It may be used as enema, but as it is quite insoluble in water it must be suspended in a mucilaginous vehicle such as decoction of marsh mallow. The best way of doing this is by mixing the quantity of naphthalin required (15-75 grains) with 2 or 3 fluid ounces of boiling distilled water, and stirring until it is diffused in very fine drops throughout the liquid. It should then be poured into 15 or 30 fluid ounces of boiling marsh-mallow tea and vigorously stirred. The liquid is then allowed to cool, and introduced into the rectum by a soft tube and funnel (p. 484).
Action. - It destroys low organisms and prevents the germination of their spores. It is a powerful antiseptic, but must be intimately mixed with the substances on which it is to have this action. It has little or no poisonous action on the higher animals when given either by inhalation or internally, the reason probably being that it is so sparingly soluble that it is not absorbed in sufficient quantity from the intestinal canal to be injurious to the organism. When given internally it disinfects the whole contents of the intestinal canal, so that the feces have either no smell at all or a faint smell of naphthalin. It is so sparingly soluble that most of it remains in the intestine and acts on the contents of the intestinal tube along its whole length from the stomach to the rectum. It is excreted in the urine, partially unchanged and partially as naphthol and perhaps phenol.