Oseltamivir

Pregnancy

MotherToBaby reports that researchers have not found a higher chance of miscarriage after oseltamivir and that several studies did not find an increased chance of birth defects. The 2017 multinational register study included 5,824 pregnancies exposed to neuraminidase inhibitors; 74% of exposed women had received oseltamivir. It found no increased overall risk of congenital malformations or other measured newborn outcomes, but Scandinavian sites excluded women hospitalized with influenza. The 2018 Danish registry included 946,176 pregnancies and 1,898 oseltamivir exposures. It found no association with major malformations or spontaneous abortion, but reported a possible heart-defect signal based on seven exposed cases; the estimate was imprecise, and similar signals appeared at exposure times not expected to cause those defects. The Danish study was funded by Roche, and company employees were involved in design, interpretation, writing, and submission. A 2022 meta-analysis of nine cohort studies found no increase in congenital malformations, low Apgar score, or preterm birth; analyses limited to oseltamivir were consistent. The Tamiflu label summarizes observational studies of more than 5,000 pregnant women, including more than 1,000 first-trimester exposures, with no higher observed malformation rate; it cautions that study sizes, comparison groups, and missing dose data limit a definitive assessment. The label also reports no adverse developmental effects at clinically relevant exposures in animal studies, which are not human outcome data. A 2026 Taiwan birth cohort of 2,231,264 mother-child pairs found no significant ADHD association for prenatal oseltamivir in its sibling comparison, but the estimate was imprecise. A 2026 study of FDA adverse-event reports found reporting signals including congenital intestinal obstruction and placental necrosis. The reports cannot establish cause or event rates. A 2026 umbrella review of 43 reviews and 27 pregnancy cohorts reported a favorable evidence profile for oseltamivir, while noting that most evidence was observational with moderate-to-low certainty; its abstract does not provide an oseltamivir-specific effect estimate. Pregnancy evidence is mainly observational. The Australian guideline's recommendation against oseltamivir applies to critically ill adults, including pregnant adults; its evidence report cites one adult critical-care trial and notes serious risk-of-bias concerns.

Breastfeeding

MotherToBaby says oseltamivir passes into milk in small amounts and has not been shown to cause side effects in nursing babies. The 2011 Greer study measured milk and plasma levels after one dose in seven healthy postpartum women who were bottle-feeding; it did not study infant outcomes. The 2024 Fodor study measured milk, colostrum, and blood levels in six lactating patients with influenza during a five-day course; estimated infant exposure was below a treatment dose, but infant levels and effects were not measured. LactMed reports that relevant published infant-level and infant-effect information was not found as of its February 15, 2024 revision. NHS SPS calls oseltamivir the preferred antiviral during breastfeeding, limits its recommendation to full-term, healthy infants, and advises monitoring for vomiting, diarrhea, irritability, and sleep changes. The Tamiflu label reports low milk levels, says postmarketing reports had not suggested serious infant effects, and states that the effect on milk production is unknown.

What was tested

Pregnancy studies used population registries and observational cohorts to examine malformations, miscarriage, preterm birth, stillbirth, fetal growth, and newborn outcomes. They cannot fully separate the medicine's effects from influenza severity and other differences between exposed and unexposed pregnancies. Breastfeeding studies measured drug levels in milk and blood; the primary studies did not follow infant health outcomes. The Australian critical-care recommendation concerns adults with acute failure of one or more vital organs who need respiratory or blood-pressure support; it is not a pregnancy-specific trial result. The Tamiflu label also summarizes animal developmental studies, which are not equivalent to human pregnancy data.