Animal studies have failed to reveal evidence of teratogenicity; animal data (with doses 2 to 100 times the maximum recommended human dose) have revealed that the drug crosses the placenta. There are no controlled data in human pregnancy; data from postmarketing reports and observational studies (over 1000 exposed outcomes during the first trimester) showed no malformative nor fetal/neonatal toxicity by this drug.

Published prospective and retrospective observational studies of about 1500 women exposed to this drug during pregnancy (including about 400 exposed in the first trimester) indicate no increase in the observed rate of congenital malformations above the general comparison population, regardless of when exposure occurred during the gestation period. However, when each study was evaluated separately, all had inadequate sample sizes and some lacked dosing information, preventing definitive assessment of risk.

Pregnant women have higher risk of severe complications from influenza, which may lead to adverse pregnancy and/or fetal outcomes.

AU TGA pregnancy category B1: Drugs which have been taken by only a limited number of pregnant women and women of childbearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed. Studies in animals have not shown evidence of an increased occurrence of fetal damage.

US FDA pregnancy category C: Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.

This drug should be used during pregnancy only if the benefit outweighs the risk to the fetus.

AU TGA pregnancy category: B1
US FDA pregnancy category: C

Comments:
-Maternal and embryo/fetal risk due to the mother's underlying condition, available safety data, and pathogenicity of circulating influenza virus strain should be considered.
-According to the US CDC, this drug is preferred for treatment of pregnant women with suspected/confirmed influenza.

See references

Caution is recommended; benefit should outweigh risk.

Excreted into human milk: Yes (parent drug and active metabolite in low levels)

Comments:
-Low levels in milk are not expected to cause harmful effects in the nursing infant.
-Low levels in milk resulting in a subtherapeutic dose to the infant, pathogenicity of circulating influenza virus strain, and underlying maternal condition should also be considered.

Based on limited data, parent drug (oseltamivir) and its active metabolite (oseltamivir carboxylate) are poorly excreted into breast milk. Maternal doses of 150 mg/day produced low levels in milk.

At 0, 0.5, 1, 2, 4, 8, 12, and 24 hours after a single 75 mg oral dose, milk samples were donated by 7 postpartum women bottle feeding their infants. Parent drug and active metabolite were measured in milk samples. The peak milk levels of parent drug and active metabolite averaged 26.9 mcg/L about 3.4 hours after the dose and 41.9 mcg/L about 18.9 hours after the dose, respectively. Based on AUC data reported in the paper and standardized milk intake of 150 mL/kg/day, a fully breastfed infant would receive about 0.9 mcg/kg/day of parent drug and 3.6 mcg/kg/day of active metabolite. The usual maternal dose (75 mg twice a day) would double these values, but the total is much less than doses reportedly used in infants (1 to 7 mg/kg/day).

A woman who was breastfeeding her 9-month-old infant received 75 mg orally twice a day for 5 days after accidentally sticking herself with a needle contaminated with 2009 H1N1 influenza virus. Breastfeeding was stopped during this time due to possible side effects in the infant. Eleven milk samples were collected twice daily over the 5-day period by completely emptying both breasts. The sample timing varied, with 8 of the samples collected 30 minutes before or after a dose. The steady-state concentration of the active metabolite was reached after 3 days and averaged 37 to 39 ng/mL. The maximum relative infant dose (parent drug plus active metabolite) was estimated to be 0.012 mg/kg/day, or about 0.5% of the mother's weight-adjusted dose (assuming 60 kg body weight). Based on this study, the drug level in breast milk appears to be clinically insignificant. Also, the potential dose for a nursing infant is much less than the pediatric dose.

The US CDC recommended women infected with 2009 H1N1 influenza virus breastfeed, regardless of whether they were being treated, due to the advantages of breast milk for the infant's immune system.

See references