Oral TDLO (rat): 10 mg/kg; Oral LD50 (mouse): 78 mg/kg; Oral TDLO (mouse): 100 mg/kg ^F3985

Use in pregnancy

Reproductive studies have been completed using rats and rabbit models at doses up to twenty times the normal human dose ( about 5 mg/kg per day), and it was concluded that fertility was not impaired and there was no fetal harm. There is a published report of a study in pregnant mice administered 50 or 100 mg/kg allopurinol intraperitoneally on gestation days 10 or 13. There were increased numbers of dead fetuses in dams administered 100 mg/kg allopurinol, however, death did not occur in those given 50 mg/kg. There were higher numbers of external malformations in fetuses at both doses of allopurinol on gestation day 10 and higher numbers of skeletal malformations in fetuses at both doses on gestation day 13. Despite the above findings, there are no adequate or well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if it is absolutely required ^{FDA label}.

Use in nursing

Both allopurinol and the metabolite oxipurinol have been found in the milk of a mother who was receiving allopurinol. Since the effect of allopurinol on the nursing infant is unknown, it is advisable to exercise caution when allopurinol is taken by a nursing woman ^{FDA label}.

Mutagenicity and carcinogenicity

Cytogenic studies demonstrate that allopurinol does not induce chromosomal abnormalities in human blood cells in vitro at concentrations up to 100 g/mL and in vivo at doses up to 60 mg/day for an average duration of 40 months. Allopurinol does not form nitroso compounds (which may be carcinogenic) or affect lymphocyte transformation in vitro. Evidence suggests that allopurinol does not have deleterious effects on DNA at any stage of the cell cycle and was not found to be mutagenic. No evidence of carcinogenicity has been observed in mice treated with allopurinol for up to a 2 year period ^F3988.