Carcinogenicity testing of acetaminophen in F344 rats.

A study of acetaminophen (AAP) for possible carcinogenicity was conducted by administering the test chemical in pelleted diets to F344/DuCrj rats of each sex. Groups of 50 rats were administered AAP at one of two doses, either 0.45 or 0.9% for males and 0.65 or 1.3% for females. The rats were treated for 104 weeks, and then observed for 26 weeks. Control groups of 50 rats were fed basal diet throughout the study. Mean intakes of AAP by low- and high-dose rats were 195.4 and 402.1 in the males, and 335.7 and 688.0 mg/kg/day in the females, respectively. The survival rates at week 104 of each group were 86 to 90% in the males and 80 to 82% in the females. No pathologic or statistical evidence of induction of tumors by AAP was found. It is concluded that, under the conditions of this study, acetaminophen is not carcinogenic to F344/DuCrj rats of either sex.