it has not been possible to avoid exposure during early organogenesis, in most instances. Nevertheless, it is theoretically possible to lower the leflunomide level substantially before organogenesis begins, if pregnancy is diagnosed at the time of the first missed menstrual period and the washout is begun immediately. Therefore, in most instances, the mother has to be told that there is a theoretical risk that the fetus may have been affected, based on animal studies.
The sensitive period for the interference with neuronal cell migration and proliferation is between the 8th and 15th week of pregnancy. Washouts that begin in the third week post conception, would prevent the risk of microcephaly and mental retardation, but would not prevent effects during early organogenesis.
Men taking leflunomide who inseminate their partner have a much different situation. Leflunomide and its main metabolites do not have mutagenic potential and TFMA is a weak mutagen and is present in extremely low concentrations. Therefore , the theoretical risk of a chromosome abnormality or a point mutation at the molecular level is extremely small. This is also true for women who have a washout before they get pregnant..
When enough human experience with inadvertent exposure to men fathering children while on leflunomide is accumulated, , we may conclude that men taking leflunomide need not consider stopping the medication if they contemplate having children, because leflunomide and its main metabolites do not have mutagenic potential and TFMA is a weak mutagen and is present in extremely low concentrations.
C. Breast Feeding
The package insert indicates that mothers who are taking leflunomide should not breast feed their infants. Phamacokinetic data concerning the level of leflunomide in breast milk is not available in order to determine the leflunomide exposure to a breast-feeding infant. It is possible that the