Pregnancy: Letrozole may cause fetal harm when administered to a pregnant woman. Reproduction studies in rats at doses equal or greater than 0.003 mg/kg (about 1/100 the daily maximum recommended human dose on a mg/m2 basis) administered during the period or organogenesis, have shown that letrozole is embrotoxic and fetotoxic, as indicated by intrauterine mortality, increased post implantation loss, decreased numbers of live fetuses and incomplete ossifications of frontal skull and metatarsals. Letrozole was teratogenic in rats. A 0.03 mg/kg doses (about 1/10 the daily maximum recommended human dose on an mg/m2 basis) caused fetal domed head and cervical/centrum vertebral fusion.
Letrozole is embriotoxic at doses equal to or greater than 0.002 mg/kg and fetotoxic when administered to rabbits at 0.02 mg/kg respectively (about 1/100.000 and 1/10.000 the daily maximum recommended human dose on an mg/m2 basis, respectively). Fetal anomalies included incomplete ossification of the skull, sternebrae, and fore and hind legs.
There are no studies in pregnant women. Letrozole is indicated for postmenopausal women. If there is exposure to letrozole during pregnancy, the patient should be apprised of the potential hazard to the fetus and potential risk for loss of the pregnancy.
The physician needs to discuss the necessity of adequate contraception with women who have the potential to become pregnant including women who are perimenopausal or who recently became postmenopausal, until their post menopausal status is fully established.