ANTIPYRINE, a colourless and slightly bitter alkaloidal substance derived from coal tar, used in medicine as an antipy retic and analgesic, called also phenazonum and analgesine. It melts at 113° C, is soluble in 1.3 parts of water and dissolves even more readily in alcohol. It reduces the temperature of fevers and pyrexia of pneumonia, pleurisy and phthisis. It relieves loco motor ataxy, facial neuralgia and rheumatism. Administered hypodermically it is beneficial in lumbago, sciatica and angina pectoris. A skin rash has been observed after its use, poisonous effects have been noticed with injudicious usage, and it has even been employed homicidally. The safe dose is .03 grams (5 grains). In aqueous solution it has a mild anaesthetic action when painted on the mucous membrane.
Antipyrine was first prepared (1884) by L. Knorr. In study ing the condensation of acetoacetic ester (q.v.) with phenyl hydrazine, this investigator obtained phenylmethylpyrazolone, a substance which has since proved useful as an intermediate for certain azo-dyes (see DYES : SYNTHETIC). Methylation of this pyrazolone derivative led to phenyldimethylisopyrazolone (I. antipyrine).
The success attending the use of antipyrine in therapeutics led to many researches in the pyrazolone series, and out of these the most important drug obtained was Pyramidon or Dimethylamino antipyrine (formula II.) which had similar uses to antipyrine but was efficacious in smaller doses and of special effect in sciatica. In its preparation, antipyrine was converted into the green nitroso antipyrine by the action of nitrous acid. Reduction with zinc dust and acetic acid led to aminoantipyrine (yellow needles, m.p. 109° C) which was methylated with methyl iodide in methyl alcoholic potash. Pyramidon is a white powder melting at io8°, soluble in nine parts of water. Both antipyrine and pyramidon are used in combination with other drugs. Salipyrine (antipyrine sali cylicum) is antipyrine salicylate, employed in acute rheumatic fever, sciatica and chronic rheumatism. Acetopyrine (antipyrine acetosalicylate), an analgesic and antipyretic, is used in sciatica, influenza, etc. Amidopyrine acetosalicylate and veramon (amido antipyrine diethylbarbiturate) are salts of pyramidon with aspirin and veronal respectively, used in headache and neuralgia.
(G. T. M.)