Is Oseltamivir (Tamiflu) safe to use during pregnancy?

Oseltamivir Safety in Pregnancy

Oseltamivir (Tamiflu) can be used during pregnancy when the potential benefit justifies the potential risk to the embryo or fetus, as pregnant women are at higher risk for influenza complications. 1, 2

Safety Profile in Pregnancy

• Oseltamivir is classified as "Pregnancy Category C," indicating no clinical studies have specifically assessed its safety in pregnant women 1, 3
• No adverse effects have been reported among women who received oseltamivir during pregnancy or among infants born to such women 1
• Pregnancy should not be considered a contraindication to oseltamivir use, as pregnant women are known to be at higher risk for complications from influenza infection 1
• A retrospective cohort study found no evidence of an association between oseltamivir use during pregnancy and adverse events including preterm birth, premature rupture of membranes, increased hospital stay, malformations, or fetal weight 1
• A study of 232 maternal exposures to oseltamivir found that the incidence of adverse pregnancy outcomes was not higher than background rates: spontaneous abortions 6.1%, therapeutic abortions 11.3%, and pre-term deliveries 2.1% 4
• A more recent study (2019) found no evidence of increased risks for birth defects, preterm delivery, or small for gestational age infants following oseltamivir exposure during pregnancy 5

Pharmacokinetic Considerations

• Pregnancy alters the pharmacokinetics of oseltamivir carboxylate (the active metabolite), resulting in lower systemic levels compared to non-pregnant women 6
• The area under the plasma concentration time curve is significantly lower and clearance significantly higher in pregnant women compared with nonpregnant women 6
• This may potentially affect dosing requirements during pregnancy, though current guidelines do not specify pregnancy-specific dosing 6

Recommendations for Use

• Oseltamivir is preferred for treatment of pregnant women with suspected or confirmed influenza 1
• Treatment should begin as early as possible after onset of illness and should not be delayed while waiting for results of diagnostic testing 1
• Pregnant women should receive the same antiviral dosing as nonpregnant persons 1
• The benefits of treatment likely outweigh potential risks, especially considering the increased risk of complications from influenza infection during pregnancy 1, 4

Common Side Effects

• The most common side effects of oseltamivir are gastrointestinal symptoms:
  • Nausea without vomiting (approximately 10% vs. 6% with placebo) 1, 3
  • Vomiting (approximately 9% in adults vs. 3% with placebo) 1, 3
  • Diarrhea (reported in less than 5% of patients) 3
• Taking oseltamivir with food may reduce the severity of nausea and vomiting 1, 3

Important Considerations

• Influenza infection during pregnancy increases risks for adverse outcomes for both mother and fetus 5
• The physiologic adaptations of pregnancy may alter the pharmacokinetics of oseltamivir, potentially requiring dosage adjustments in some cases 7, 6
• When making treatment decisions, clinicians should consider the available safety information, the pathogenicity of the circulating influenza virus strain, the woman's general health, and guidance from health authorities 4

Monitoring

• Monitor for common side effects such as nausea and vomiting 3
• Be aware of potential neuropsychiatric events, though these are rare and primarily reported in adolescents and adults in Japan 1, 3