May 23 2022

Classification of the active ingredient allopurinol


Risk level in pregnancy: This medicine is classified as Category C.

There are no adequate and well-controlled studies in pregnant women regarding the use of this medicine.

Few observations have been published on the use of allopurinol during pregnancy, as this drug is rarely used in women of childbearing age. Perhaps for this reason it has been published a very low number of adverse effects in children exposed to the drug.

In general, reproduction studies in rats and rabbits at doses up to twenty times the usual human dose (5 mg / kg per day), have not shown impaired fertility or harm to the fetus, although one study on mice showed cleft palate and skeletal defects upon exposure to allopurinol, but these or other effects have not been reproduced in other species.

In four pregnant women treated with doses of 300-400 mg / day of allopurinol associated with chemotherapy for the treatment of leukemia from the second trimester of pregnancy, showed two normal births, one fetal death and one case of delayed intrauterine growth with liver calcifications, aplasia of one kidney and hydronephrosis of the opposite. Not established a causal link.

Given that animal reproduction studies are not always predictive of what happens in humans, this drug should be used during pregnancy only if clearly needed.

Update 18.07.2009

Meaning of category C

Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.