Use in Pregnancy: Letrozole may cause fatal harm when administered to pregnant women. Studies in rats at doses equal to or greater than 3 mcg/kg (about 1/100 the daily maximum recommended human dose on a mg/m2 basis) administered during the period of organogenesis, have shown that letrozole is embryotoxic and fetotoxic, as indicated by intrauterine mortality, increased resorption, increased postimplantation loss, decreased numbers of live fetuses and fetal anomalies including absence and shortening of renal papilla, dilation of ureter, edema and incomplete ossification of frontal skull and metatarsals. Letrozole was teratogenic in rats. A 30 mcg/kg dose (about 1/10 the daily maximum recommended human dose on a mg/m2 basis) caused fetal domed head and cervical/centrum vertebral fusion. Letrozole is embryotoxic at doses equal to or greater than 2 mcg/kg and fetotoxic when administered to rabbits at 20 mcg/kg (about 1/100,000 and 1/10,000 the daily maximum recommended human dose on a mg/m2 basis, respectively). Fetal anomalies included incomplete ossification of the skull, sternebrae, and fore- and hindlegs. There are no studies in pregnant women. Letrozole tablets is indicated for post-menopausal women. If there is exposure to letrozole during pregnancy, the patient should be apprised of the potential of the potential hazard to the fetus and potential risk for loss of the pregnancy.
Use in Lactation: It is not known if letrozole is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when letrozole is administered to a nursing woman.