pharmacological substances of various chemical structures that have a fever-reducing, analgesic (pain-relieving), and anti-inflammatory effect. Antipyretics include derivatives of salicylic acid (sodium salicylate, acetylsalicylic acid, salicylamide, and methyl salicylate), pyrazolone (antipyrine, aminopyrine, Analgin, and Butadion), and aniline (phenacetin and acetaminopen). Antipyretics are often combined with each other or with caffeine to strengthen their pharmacological effect. The most widely used combinations are Analgin + aminopyrine + caffeine; askofen + acetylsalicylic acid + phenacetin + caffeine; tsitramon + acetylsalicylic acid + phenacetin + caffeine + cacao + citric acid + sugar; and pirafen (aminopyrine + phenacetin). The combined preparation reopirin (Butadion + aminopyrine) is produced in Hungary;piranal (aminopyrine + Analgin) and sedalgin (codeine + caffeine + phenacetin + acetylsalicylic acid + phenobarbital) are produced in Bulgaria.

The antipyretic effect of these substances is observed if they are administered to an organism that is suffering from fever; at normal body temperatures there is no lowering of temperature. The antipyretic effect is explained by the selective action of the antipyretics on the heat-regulation centers of the body; increased heat loss occurs, which is caused by the dilation of the skin blood vessels, increased secretion of the sweat glands, and acceleration of respiration. The analgesic effect of antipyretics is not completely understood; it is thought that they act on the pain centers of the brain. The anti-inflammatory properties of the salicylates are associated with their stimulating effect on the pituitary and an increase in the secretion of adrenocorticotropic hormone (ACTH). They decrease the activity of the enzyme hyaluronidase and lower the permeability of the capillaries. These properties of antipyretics determine their therapeutic use for headaches, neuralgia, and muscle and joint pains, as well as their use as anti-inflammatory agents for acute rheumatic fever, non-rheumatoid arthritis, and exudative pleurisy.

Antipyretics are usually taken internally, but methyl salicylate is applied externally (for rubdowns), according to a doctor’s instructions. Complications may arise during prolonged use of antipyretics. The side effects of salicylic acid derivatives include nausea, vomiting, noise in the ears, irritation, and sometimes ulceration of the mucous lining of the stomach; the derivatives of pyrazolone may suppress leuko-poiesis and cause agranulocytosis, and aniline derivatives may cause the formation of methemoglobin. As a rule, all of these complications disappear after the medication is discontinued.