Is oseltamivir (Tamiflu) safe to use during pregnancy?

Is Tamiflu (Oseltamivir) Safe in Pregnancy?

Yes, oseltamivir is safe and strongly recommended for pregnant women with suspected or confirmed influenza, regardless of trimester, and the benefits of treatment far outweigh any theoretical risks. 1, 2, 3

Key Safety Evidence

The FDA label explicitly states that published observational studies of more than 5,000 pregnant women exposed to oseltamivir, including over 1,000 women in the first trimester, show no increased risk of birth defects compared to the general population. 2

• Observational data demonstrate no association between oseltamivir use and adverse outcomes including preterm birth, premature rupture of membranes, congenital malformations, or abnormal fetal weight 4
• No adverse effects have been reported among women who received oseltamivir during pregnancy or among infants born to such women 1, 4
• The CDC explicitly states that "pregnancy should not be considered a contraindication to oseltamivir use" 4, 5

Treatment Recommendations

The American College of Obstetricians and Gynecologists recommends oseltamivir 75 mg orally twice daily for 5 days for any pregnant woman with suspected or confirmed influenza, regardless of trimester or vaccination status. 1, 3

• Treatment should begin immediately upon clinical suspicion—do not wait for laboratory confirmation 3
• Treatment is beneficial even if started beyond 48 hours of symptom onset 3
• Standard adult dosing applies: 75 mg twice daily for treatment, 75 mg once daily for prophylaxis 1

Clinical Rationale for Aggressive Treatment

Pregnant women face substantially higher risks from influenza infection than from oseltamivir treatment:

• Pregnant women are at higher risk for severe illness, pneumonia, ICU admission, and death compared to non-pregnant women 1
• The relative risk for hospitalization increases from 1.4 at 14-20 weeks gestation to 4.7 at 37-42 weeks 1
• Influenza infection during pregnancy is associated with maternal death, stillbirths, birth defects, preterm delivery, low birth weight, and small-for-gestational-age infants 1, 2
• Observational data show oseltamivir reduces severe outcomes in pregnant women without increased risk of adverse maternal, fetal, or neonatal outcomes 6

Important Clinical Caveats

The FDA classifies oseltamivir as Pregnancy Category C, but this cautious language reflects the lack of controlled trials (which are ethically difficult to conduct in pregnancy), not evidence of harm. 4, 2

• The extensive post-marketing surveillance data and experience from the 2009 H1N1 pandemic demonstrate both the severe risks of untreated influenza in pregnancy and the reassuring safety profile of oseltamivir 4
• Animal studies showed minor skeletal abnormalities only at doses 190 times the maximum recommended human dose 2
• Common side effects (nausea 10%, vomiting 8-9%) are typically mild, transient, and reduced by taking with food 4

Alternative Agent

Zanamivir 10 mg (two 5 mg inhalations) twice daily for 5 days can be used if oseltamivir is contraindicated or unavailable. 1

• Zanamivir is also approved for use during pregnancy, particularly for high-risk and moderate-risk exposure groups 1
• Zanamivir has lower systemic bioavailability than oseltamivir 7

Post-Exposure Prophylaxis

For pregnant women with high-risk or moderate-risk exposure to influenza, oseltamivir 75 mg once daily for 7-10 days after last known exposure is recommended. 7, 1

• Pregnant women in low-risk exposure groups should not receive prophylaxis, as this places higher value on avoiding possible but uncertain harm when disease risk is low 7

Additional Management

• Use acetaminophen for fever management, as fever itself can cause adverse fetal outcomes 5
• Monitor for warning signs requiring urgent evaluation: difficulty breathing, chest pain, persistent high fever, decreased fetal movement, or signs of preterm labor 1