This section is from the book "Botanic Drugs Their Materia Medica, Pharmacology and Therapeutics", by Thomas S. Blair. Also available from Amazon: Botanic Drugs, Their Materia Medica, Pharmacology and Therapeutics.
As an antiseptic, salicylic acid is little used externally, other substances being preferable. The salts of salicylic acid pass so rapidly from the intestine as to possess little antiseptic action there. It is also excreted from the blood so freely that it does not occur in sufficient concentration to be markedly antiseptic in the bloodstream. But the salicylates enter into nearly all of the secretions.
The antipyretic action is not especially important and is due to the diaphoresis induced rather than to any antiseptic effect. The cholagogue action is slight.
If there is any renal inflammation use the salicylates cautiously, as grave symptoms may supervene. In the presence of cardiac symptoms, the salicylates have the reputation of being deleterious; but the matter is not definitely determined. Some authorities claim that they diminish the liability to pericarditis, while others assert an increase in the percentage of rheumatic cases resulting in endocarditis.
Externally, a 3 per cent powder in any inert medium is used for dusting sweating feet and for the removal of corns (1 drachm in an ounce of flexile collodion). In dermatology it is esteemed in affections characterized by thickening of the epidermis and in parasitic diseases. It may be used in weak solution as a mouth wash.
In gout the salicylates are less esteemed than formerly. My own view is that certain manifestations of gout, not the disease itself, are met successfully with the salicylates. The pains of gout and tabes dorsalis, sciatic pain, and some cases of migraine, are assuredly relieved by the salicylates; but the cure of gout requires more brisk elimination than that afforded by the salicylates alone. Somewhat the same view may be held as regards its action in lithemia. However, the salicylates do increase the excretion of uric acid; but the so-called uric acid diathesis has been vastly overstated.
In conditions associated with serous effusions the salicylates may be of value. Perhaps its failing reputation in the treatment of pneumonia was dependent upon relief in cases that were complicated with pleuritic effusions and not upon any direct influence upon pneumonia itself.
In interstitial keratitis large doses have been given with excellent response. Quinsy responds fairly well to the salicylates, as well as tonsillar infections.
Waller has claimed that the salicylates influence thyroid activity; hence its use in Graves' disease and thyroiditis is suggested.
But by far the most important use of the salicylates is in rheumatism. This use is proven out thoroughly by clinical experience, though not pharmacologically. Gaglio has advanced a theory to the effect that the action of the salicylates in rheumatism is due to the rapid excretion into the joints (by the synovial membranes) of the salt, as received from the blood.
In rheumatism, in the form of acute rheumatic fever, the sodium salicylate must be begun at once and in full dosage, well diluted with water, and even as high as 20 grains every three hours for the first twenty-four hours; then half as much as first given thrice daily for quite a period. It is well to give sodium bicarbonate with the salicylate.
Many so-called cases of rheumatism are not such; in fact, most cases of chronic arthritis are not, being due to other infections, such as gonorrhea; therefore the salicylates must be used in so-called "chronic rheumatism" with considerable diagnostic discrimination.
Doses of salicylic acid range from 2 to 15 grains; of sodium salicylate, from 5 to 30 grains.
Methyl Salicylate is prepared from the natural oil and may be used externally as an application to painful joints, but should not be taken internally. It would better be diluted, as it appears to be stronger than the synthetic methyl salicylate. Oils of Gaultheria (wintergreen) and Betula (sweet birch) are about 90 per cent methyl salicylate. Dose, 10 to 15 drops. Salicin is given in doses of 5 to 30 grains and is less energetic than salicylic acid. It is well borne by the stomach and is of slight toxicity. It is slow in action. Xanol is a caffeine-sodio salicylate from natural oil and is a cardiac stimulant. Salicylic Acid Compounds are more or less insoluble, especially the esters, the salicyl radical being liberated in the intestine or after absorption. In practice these synthetic preparations are not superior in effect to sodium salicylate, especially that from the natural oil. They are, however, nearly tasteless, most of them, and are very expensive. For a description of these synthetic products see "New and Nonofficial Remedies"; and for a description of the many salts of synthetic salicylic acid see the general text-books.