Allopurinol is a hypoxanthine analogue that inhibits xanthine oxidase, thereby decreasing the production of uric acid. Exposure in females of childbearing age is most commonly in the treatment of inflammatory bowel disease (IBD). Allopurinol is also used in the management or prophylaxis of gout, uric acid or calcium oxalate renal calculi, hyperuricaemia associated with cancer chemotherapy, as a thiopurine adjunct in renal transplant recipients, and in the treatment of protozoan infections.
Allopurinol is sometimes used in pregnant women with IBD, often as adjunctive therapy. Effective control of IBD is crucial in pregnancy for both maternal wellbeing and to mitigate the risks of some adverse pregnancy outcomes associated with active (uncontrolled) IBD, including miscarriage, preterm delivery, and reduced fetal growth.
Published case reports describe the presence/absence of congenital malformations for a collective total of just 43 live-born infants following first trimester exposure. Overall, 41 infants were born without major congenital malformations (MCMs). While two infants with MCMs (reported in 2011 and 2013) had a partially overlapping malformation pattern, a genetic basis for the malformations was not fully explored and a causal association with allopurinol exposure cannot be established. No subsequent publications have described major congenital malformations in allopurinol-exposed infants.
Miscarriage rates were not increased above background rates in a prospective case series (n=31). However, conclusions are limited by the small sample size and lack of a control group. Data are either too limited or are unavailable to assess the risks of other adverse pregnancy outcomes.
If allopurinol use is being considered in pregnancy, the benefits of effective disease control vs. the possible risks to the fetus should be discussed with the patient. Other factors may also be present in individual cases which may independently increase the risk of adverse pregnancy outcome. Clinicians are reminded of the importance of consideration of such factors when performing case-specific risk assessments.
In order that further outcome information is formally collected for women who have taken allopurinol in pregnancy, please report any exposed pregnancies to UKTIS using the pregnancy reporting form.
This is a summary of the full UKTIS monograph for health care professionals and should not be used in isolation. The full UKTIS monograph and access to any hyperlinked related documents is available to NHS health care professionals who are logged in.
If you have a patient with exposure to a drug or chemical and require assistance in making a patient-specific risk assessment, please telephone UKTIS on 0344 892 0909 to discuss the case with a teratology specialist.
If you would like to report a pregnancy to UKTIS please click here to download our pregnancy reporting form. Please encourage all women to complete an online reporting form.