Is Oseltamivir (Tamiflu) safe during pregnancy?

Oseltamivir Safety in Pregnancy

Oseltamivir is safe to use during pregnancy and should be prescribed when indicated for influenza treatment or prophylaxis, as pregnant women are at significantly higher risk for severe influenza complications and the benefits clearly outweigh any theoretical risks. 1, 2

Key Safety Evidence

Pregnancy Category and Clinical Data

• Oseltamivir is classified as FDA Pregnancy Category C, meaning adequate clinical studies in pregnant women have not been conducted 3, 2
• However, published epidemiological data from over 5,000 pregnant women exposed to oseltamivir, including more than 1,000 first-trimester exposures, show no increased risk of birth defects above baseline population rates 2
• Post-marketing surveillance data from 2,128 pregnant women showed adverse pregnancy outcomes at rates lower than background population rates: spontaneous abortion 2.9% (vs. 15-20% baseline), therapeutic abortion 1.8%, and preterm delivery 4.2% 4

Birth Defect Analysis

• Among 81 reported birth defect cases in the Roche safety database, only 11 occurred during the sensitive period for the respective defects, with no causal pattern suggesting oseltamivir exposure as the cause 4
• Animal reproduction studies showed no adverse developmental effects at clinically relevant exposures 2
• One retrospective cohort study found no association between oseltamivir use during pregnancy and preterm birth, premature rupture of membranes, malformations, or abnormal fetal weight 1

Clinical Recommendations

When to Prescribe

Pregnant women with suspected or confirmed influenza should receive oseltamivir treatment immediately, without waiting for diagnostic test results 1

• Pregnant women are at higher risk for influenza complications including maternal death, stillbirths, preterm delivery, and low birth weight 2
• Treatment should begin as early as possible after symptom onset 1

Dosing in Pregnancy

• Use the same dosing as nonpregnant patients: 75 mg twice daily for treatment, 75 mg once daily for prophylaxis 1
• Note that pregnancy increases clearance of the active metabolite (oseltamivir carboxylate), resulting in lower systemic levels 5, though current standard dosing remains recommended 1

Adverse Effects to Anticipate

• Nausea (10%) and vomiting (9%) are the most common side effects 3
• Taking oseltamivir with food significantly reduces gastrointestinal symptoms 3, 2
• Acetaminophen should be used for fever management, as fever itself can cause adverse fetal outcomes 1

Important Caveats

Risk-Benefit Context

The older ACIP guidelines 1 stated that oseltamivir "should be used during pregnancy only if the potential benefit justifies the potential risk to the embryo or fetus" based on lack of clinical trial data. However, this cautious language predated the extensive post-marketing surveillance data and the 2009 H1N1 pandemic experience, which demonstrated both the severe risks of influenza in pregnancy and the safety profile of oseltamivir 1, 2, 4.

Current Evidence Hierarchy

• The 2011 CDC guideline explicitly states that "pregnancy should not be considered a contraindication to oseltamivir use" 1
• The FDA label (2025) confirms that available epidemiological data suggest oseltamivir is not associated with increased risk of birth defects in any trimester 2
• Post-marketing data from nearly 3,000 exposures reinforce the safety profile 4

Lactation Safety

• Oseltamivir and its active metabolite are present in breast milk at low levels considered unlikely to cause toxicity in breastfed infants 2
• No adverse effects have been reported in breastfed infants whose mothers received oseltamivir 3