Introduction: Arava™ (leflunomide) is a pyrimidine synthesis inhibitor used in the treatment of active rheumatoid arthritis (RA). The chemical name for leflunomide is N- (4’-trifluoromethylphenyl)-5-methylisoxazole-4-carboxamide. Because the drug has been successful in the treatment of rheumatoid arthritis (RA), it is being widely prescribed. In spite of the clear warning that the drug should not be prescribed for pregnant women, approximately 30 women have become pregnant while taking leflunomide as of December 1999. This commentary was prepared to aid teratology counselors and genetic counselors that might be contacted by physicians or patients about the risk of leflunomide exposure during pregnancy. Before the subject of risk is discussed, it would be important to understand the results of preclinical testing, phamacokinetic studies and clinical studies that are available.
II. Background Information:
Preclinical and clinical studies pertaining to the reproductive risks of preconception and postconception exposures to leflunomide, a new drug, marketed by Aventis became available for analysis and interpretation. Utilizing the basic science principals of teratology and the preclinical reproductive toxicology studies, an attempt was made to estimate the reproductive risks of leflunomide. All of the preclinical and clinical data that was prepared for submission to the Food and Drug administration were available for analysis.
The scientists and clinicians of Aventis concluded that Arava™ should not be administered to pregnant women. The drug was marketed as a category X drug according to the present FDA classification. The actual wording in the product label with regard to reproductive warnings is: