Is oseltamivir (Tamiflu) safe to use during pregnancy?

Oseltamivir Use in Pregnancy

Yes, oseltamivir should be given to pregnant women with confirmed or suspected influenza, and pregnancy is not a contraindication to its use. 1, 2

Key Recommendation

Pregnant women with suspected or confirmed influenza should receive oseltamivir treatment immediately without waiting for diagnostic test results. 2 Treatment should begin as early as possible after symptom onset, as pregnant women are at significantly higher risk for influenza complications including maternal death, stillbirths, preterm delivery, and low birth weight. 1, 2

Dosing

• Use the same dosing as nonpregnant patients: 75 mg twice daily for treatment, 75 mg once daily for prophylaxis 1, 2
• No dose adjustment is needed based on pregnancy alone 1

Safety Profile

Oseltamivir is preferred over zanamivir for treating pregnant women. 1 While classified as Pregnancy Category C (indicating limited clinical trial data), extensive post-marketing surveillance demonstrates reassuring safety:

• A retrospective cohort study found no association between oseltamivir use during pregnancy and preterm birth, premature rupture of membranes, malformations, or abnormal fetal weight 1, 2
• Published observational studies of over 5,000 pregnant women exposed to oseltamivir, including more than 1,000 first-trimester exposures, showed no increased rate of congenital malformations above the general population 3
• Post-marketing data from 2,128 pregnant women showed spontaneous abortion rates of 2.9%, therapeutic abortion rates of 1.8%, and preterm delivery rates of 4.2%—all lower than background population rates 4
• A prospective cohort study of 112 oseltamivir-exposed pregnancies found 6.7% major birth defects versus 7.9% in unexposed controls (RR 0.84,95% CI 0.19-2.80) 5

Critical Context: Risk-Benefit Analysis

The risks of untreated influenza in pregnancy far outweigh any theoretical risks of oseltamivir. 1, 2 Pregnant women face:

• Higher risk for complications from seasonal and pandemic influenza 1
• Increased risk of severe disease, particularly from H1N1 infection 1
• Maternal death, stillbirths, and adverse fetal outcomes from influenza infection itself 2, 3
• Fever-related adverse fetal outcomes, which oseltamivir helps prevent by reducing illness duration and severity 1

Additional Management

• Treat fever with acetaminophen, as fever itself can cause adverse fetal outcomes 1, 2
• Do not delay treatment while awaiting diagnostic test confirmation 1, 2

Common Pitfalls to Avoid

• Do not withhold oseltamivir due to Pregnancy Category C designation. This classification reflects lack of controlled trial data (which are unethical to conduct), not evidence of harm. 1, 2
• Do not delay treatment for diagnostic testing. Early treatment is critical for high-risk patients including pregnant women. 1, 2
• Do not choose zanamivir over oseltamivir without specific indication. While zanamivir has limited systemic absorption, respiratory complications from its inhaled route are concerning, especially in women at risk for respiratory problems. 1

Pharmacokinetic Consideration

One study found pregnancy produces lower systemic levels of oseltamivir carboxylate (the active metabolite), with significantly lower AUC and higher clearance compared to nonpregnant women. 6 However, current guidelines do not recommend dose adjustment, and standard dosing remains appropriate. 1, 2