Is azathioprine (AZA) safe for pregnant women with rheumatoid arthritis (RA)?

Updated: May 11, 2018
  • Author: Katherine K Temprano, MD; Chief Editor: Christine Isaacs, MD  more...
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Azathioprine (AZA), although a category D medication, can be used if the benefits outweigh the risks. AZA crosses the placenta, but the fetal liver lacks the enzyme inosinate pyrophosphorylase, which converts AZA to its active metabolite, 6-mercaptopurine; thus, the fetus is protected from the agent's teratogenic effects.

A meta-analysis of four studies that evaluated AZA/6-mercaptopurine use in 312 pregnant women with inflammatory bowel disease (IBD) found no increased risk for spontaneous abortion, prematurity or low birth weight. However, an increased risk for congenital abnormalities was found in women taking the drug, compared with women with IBD not on medications (OR, 2.95; 95% CI, 1.03-8.43). [29]

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