Fetal Risk Summary
Oseltamivir is an ethyl ester prodrug that is metabolized primarily in the liver by esterases to oseltamivir carboxylate, the active agent. The drug is active against influenza viruses, types A and B, and is given orally for the treatment of uncomplicated acute illness due to influenza infection.
In reproduction studies, doses up to approximately 100 times the human systemic exposure based on AUC (0 to 24 hours) of oseltamivir carboxylate (HSE) had no effects on fertility or mating performance in male and female rats, or on embryo-fetal development (1). Similarly, doses in rabbits up to 50 times the HSE also had no effect on embryo-fetal development (1). In both species, fetal exposure to the antiviral agent was documented. Although a dose-dependent increase in the incidence rates of skeletal abnormalities and variants were observed in both species, the individual incidence rate of each defect remained within the expected background rates of occurrence (1).
It is not known if oseltamivir or oseltamivir carboxylate cross the placenta to the human fetus. The molecular weight (about 312 for the free base of oseltamivir) is low enough that transfer to the fetus should be expected.
No reports describing the use of oseltamivir during human pregnancy have been located. The lack of embryo and fetal toxicity in two animal species is reassuring, but an assessment of the risk this antiviral agent presents to a human embryo or fetus cannot be determined.
Breast Feeding Summary
No reports describing the use of oseltamivir during human lactation have been located. In lactating rats, both oseltamivir and oseltamivir carboxylate are excreted into milk (1). Because the molecular weight of oseltamivir (about 312 for the free base) is low enough, excretion into breast milk should be expected. The effects of this exposure on a nursing infant are unknown.
- Product information. Tamiflu. Roche Laboratories, 2000.