Leflunomide - A human teratogen? A still not answered question. An evaluation of the German Embryotox pharmacovigilance database.

The teratogenic potential of leflunomide (LEF) in humans is still a matter of debate. We evaluated exposed pregnancies of our German Embryotox pharmacovigilance database. Inclusion criteria were LEF exposure anytime between 2 years before and 10 weeks after conception and no wash-out therapy before pregnancy. Of 65 prospectively enrolled pregnancies 47 were exposed during the 1st trimester and 18 preconceptional. Wash-out therapy was confirmed in 25 pregnancies. There were 10 spontaneous abortions and 19 elective terminations. Among 39 live-born children (including twins) one major malformation was recorded. A separate analysis of our retrospective adverse drug reaction database revealed one LEF-exposed case having no malformations. Our findings provide further evidence that LEF is not a major human teratogen. However, an embryotoxic potential resulting in an increased miscarriage rate cannot be ruled out. The recommendation of a waiting period of two years and a plasma level below 0.02mg/L seems too cautious.