Vigabatrin: placental transfer in vivo and excretion into breast milk of the enantiomers.

AIMS Vigabatrin is a new antiepileptic medication consisting of a racemic mixture of 50% active S enantiomer and 50% inactive R enantiomer. Since patients suffering from epilepsy may become pregnant, it is important to understand the extent of placental transfer of such medication. METHODS During steady-state, vigabatrin enantiomer concentrations were measured in maternal and umbilical blood and in breast milk of two patients. RESULTS The concentration ratios from the umbilical vein to maternal plasma were R:0.068, S:0.16; 4h25 min after drug administration (case 1) and R: 1.39, S: 0.91; 9h after drug administration (case 2). The milk: plasma concentration ratio was lower than 1 at pre dose sampling in both cases, as well as 3 and 6 h post dose in one case. An estimate of the maximum amount of R and S enantiomers of vigabatrin that a suckling infant would ingest in a day is 3.6% and 1% of the weight-adjusted daily dose respectively. CONCLUSIONS These results would suggest a slow placental transfer of the vigabatrin enantiomers and that the quantity ingested through milk is small.