Allopurinol and Pregnancy

The FDA has assigned allopurinol (Zyloprim) a pregnancy Category C rating, meaning this medication may not be safe to use during pregnancy. Allopurinol has been shown to cause certain birth defects and miscarriages when given in high doses to pregnant mice. However, most animal studies done on allopurinol and pregnancy indicate that the drug is not likely to cause problems during pregnancy.

 

An Overview of Allopurinol During Pregnancy

Allopurinol (Zyloprim®) is a prescription medication used to prevent gout attacks, high uric acid levels in cancer patients, and certain types of recurring kidney stones. It is not clear if allopurinol is safe for pregnant women to take.
 

Pregnancy Category C

The U.S. Food and Drug Administration (FDA) uses a pregnancy category system to classify the possible risks to a fetus when a specific medicine is taken during pregnancy. Pregnancy Category C is given to medicines that have not been studied in pregnant humans, but do appear to cause harm to the fetus in animal studies. Also, medicines that have not been studied in any pregnant women or animals are automatically given a "default" pregnancy Category C rating.
 
Most animal studies have indicated that allopurinol does not cause problems during pregnancy. However, one study in mice suggested that very high doses of allopurinol might increase the risk of certain birth defects and miscarriages.
 
It is important to note that animals do not always respond to medicines in the same way that humans do. Therefore, a pregnancy Category C medicine may be given to a pregnant woman if the healthcare provider believes that the benefits to the woman outweigh any possible risks to the unborn child. There is very little information available about the use of allopurinol in pregnant women, as this medication is used to treat conditions that are uncommon in women of childbearing age.
 
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Written by/reviewed by: Kristi Monson, PharmD; Arthur Schoenstadt, MD
Last reviewed by: Kristi Monson, PharmD;