The antipyretic effect of suprofen in rats with yeast-induced fever.

The antipyretic activity of alpha-methyl--4-(2-thienylcarbonyl)benzeneacetic acid (suprofen) was studied in rats with comparable hyperthermia after s.c. injection of brewer's yeast. The lowest dose effectively reducing fever is 5 mg/kg and restoration of normal body temperature is obtained with 40 mg/kg. Hypothermia is not observed even after treatment with 160 mg/kg. The ED50 (with confidence limits), which reduces fever below 39 degrees C in 50% of the animals, at the time of peak hyperthermia is 10.0 (6.6--15.2) mg/kg. ED50's of simultaneously studied reference compounds are 5.7 (3.9--8.3) mg/kg for indometacin, 38 (24--61) mg/kg for tolmetin, 76 (47--121) mg/kg for phenylburazone and 113 (75--170) mg/kg for acetyl-salicylic acid. Two to four times higher doses of these compounds restore normal body temperature but further increase of the dose induces hypothermia, which is particularly pronounced for acetyl-salicylic acid and phenylbutazone. Suprofen is a potent antipyretic agent, devoid of hypothermic activity even at 32 times the lowest effective dose.