Findings from animal studies have suggested that leflunomide may be a human teratogen. In the only human cohort study published to date, an increase in adverse outcomes in pregnancies after exposure to leflunomide was not detected. The aim of the present analysis was to expand on the previously published data with a description of birth outcomes among women who did not meet the previous cohort study criteria but who were exposed to leflunomide either during pregnancy or prior to conception.
Data on pregnancy exposures and outcomes were collected from 45 pregnant women who had contacted counseling services of the Organization of Teratology Information Specialists in the US or Canada between 1999 and 2009. Sixteen women were exposed to leflunomide during the first trimester of pregnancy and 29 women were exposed preconception.
All 16 of the pregnancies with leflunomide exposure during pregnancy and 27 (93%) of the pregnancies with exposure prior to conception resulted in liveborn infants. There were 2 infants with major malformations from mothers who were exposed during pregnancy, and no malformations reported in the preconception group. There was a potential known alternative etiology for at least some of the defects observed.
These data provide additional reassurance to women who inadvertently become pregnant while taking leflunomide and who undergo the washout procedure, as well as women who discontinue the medication prior to conception but have no prepregnancy documentation of drug clearance. However, until more conclusive data become available, women receiving leflunomide should be advised to use contraceptive methods and avoid pregnancy.