Benefit should outweigh risk

AU TGA pregnancy category: B2
US FDA pregnancy category: Not assigned

Risk Summary: Limited data available on use of this drug in pregnant women to inform a drug-related risk.

Comments: This drug should only be used during pregnancy when there is no safe alternative and when the disease itself carries risks for the mother or child.

Administration to rats and rabbits at doses up to 20 times the usual human dose (5 mg/kg/day) did not result in fetal harm. A study in pregnant mice receiving 50 or 100 mg/kg intraperitoneally on gestation days 10 or 13 showed an increased number of external and skeletal malformations in fetuses and an increased number of dead fetuses in dams given 100 mg/kg; it cannot be determined whether this may have been a fetal effect or an effect secondary to maternal toxicity. Experience in women of reproductive age is limited due to infrequent use. A 35 year old woman with recurrent kidney stones who had been taking allopurinol since age 18, took this drug throughout pregnancy and gave birth to a full-term baby with multiple complex birth defects who later died at 8 days old. In an analysis of 31 prospectively ascertained pregnancies in mothers exposed to allopurinol for varying durations during the first trimester, an overall rate of major fetal malformations and spontaneous abortions was within the normal expected range with 1 child having severe malformations similar to the case described above. There are no adequate and well controlled trials in pregnant women.

AU TGA pregnancy category B2: Drugs which have been taken by only a limited number of pregnant women and women of childbearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed. Studies in animals are inadequate or may be lacking, but available data show no evidence of an increased occurrence of fetal damage.

US FDA pregnancy category Not Assigned: The US FDA has amended the pregnancy labeling rule for prescription drug products to require labeling that includes a summary of risk, a discussion of the data supporting that summary, and relevant information to help health care providers make prescribing decisions and counsel women about the use of drugs during pregnancy. Pregnancy categories A, B, C, D, and X are being phased out.

See references

Caution is recommended

Excreted into human milk: Yes

Comments: The effects in the nursing infant are unknown.

Allopurinol and its active metabolite oxypurinol are excreted into human breast milk. Based on a case study in a 5-week old breastfed infant, the calculated daily dose of allopurinol and oxypurinol received by an exclusively breastfed infant would be between 0.14 and 0.2 mg/kg and 7.2 to 8 mg/kg, respectively. Limited data have found no observable side effects in breastfed infants. If this drug is needed, monitor breastfed infants closely for allergic reactions (e.g. rash), and perform periodic blood counts (including a differential).

See references