What are the common side effects of oseltamivir (Tamiflu)?

Common Side Effects of Oseltamivir (Tamiflu)

The most common side effects of oseltamivir are gastrointestinal symptoms—specifically nausea (approximately 10% of adults) and vomiting (approximately 9% of adults, 14% of children)—which are typically mild, transient, and can be significantly reduced by taking the medication with food. 1, 2, 3

Gastrointestinal Effects

• Nausea without vomiting occurs in approximately 10% of adults receiving oseltamivir for treatment compared to 6% with placebo 1, 2
• Vomiting occurs in approximately 9% of adults (versus 3% with placebo) and 14% of children (versus 8.5% with placebo) 1, 2
• Diarrhea is reported in less than 5% of patients 2
• These gastrointestinal symptoms are generally mild, occur predominantly on Day 1 of treatment, and last less than 1 day 4
• Taking oseltamivir with food significantly reduces the severity of nausea and vomiting—this is the single most important strategy to minimize these effects 1, 2, 3
• Only 1% of patients discontinue oseltamivir due to gastrointestinal side effects 1, 2

Neurological Effects

• Headache is common (16.8-23.7% across dosage groups) but its incidence is unrelated to oseltamivir dosage 4
• Dizziness occurs in up to 11.3% of patients and may be dose-related 4

Serious Adverse Effects (Rare but Important)

Neuropsychiatric Events

• Transient neuropsychiatric events including self-injury, delirium, abnormal behavior, hallucinations, agitation, anxiety, altered consciousness, confusion, nightmares, and delusions have been reported during post-marketing surveillance 1, 2, 3
• The majority of these reports were among Japanese adolescents and adults 1
• Multiple recent analyses have found that oseltamivir is NOT associated with an increased risk for neuropsychiatric events, but the FDA still advises close monitoring for abnormal behavior, particularly in adolescents 1, 2, 3
• A large insurance database study showed no evidence of increased risk of neuropsychiatric events in oseltamivir recipients compared to non-recipients 5

Allergic and Skin Reactions

• Serious skin and allergic reactions can occur, including skin rash, hives, blistering and peeling skin, blisters or sores in the mouth, and oropharyngeal or facial edema 2, 3
• Stop oseltamivir immediately if any of these symptoms develop and seek medical attention 3
• However, a clear association between skin reactions and oseltamivir has not been definitively established based on post-marketing surveillance 5

Safety Profile Across Populations

Children

• Vomiting is the most common adverse effect in children (14% versus 8.5% with placebo) 1, 2
• Careful attention to dosing is essential in young children to avoid dosing errors 1

Pregnancy

• Oseltamivir is FDA Pregnancy Category C, but no adverse effects have been reported among women who received oseltamivir during pregnancy or among infants born to such women 1, 2
• The CDC explicitly states that pregnancy should not be considered a contraindication to oseltamivir use 2

Elderly and High-Risk Patients

• Similar adverse event profiles to otherwise healthy adults, with no age-related safety concerns identified 6, 5

Drug Interactions and Other Considerations

• Limited potential for drug interactions due to oseltamivir's simple pharmacology and minimal protein binding (3%) 7
• Coadministration with probenecid results in approximately 50% reduced clearance and twofold increase in plasma levels, but this is rarely clinically significant 2
• No impairment of immunologic response to influenza vaccine has been demonstrated 1, 2
• Oseltamivir has no relevant effects on vital signs, laboratory parameters, or cardiac function, including QT interval 5, 4

Clinical Monitoring Recommendations

• Monitor all patients, especially adolescents, closely for abnormal behavior during treatment 1, 2, 3
• Advise patients to take oseltamivir with food to minimize gastrointestinal symptoms 1, 2, 3
• Report serious adverse events to FDA's MedWatch program 2, 3

Important Caveats

The overall safety profile of oseltamivir is excellent based on extensive clinical trial data (>11,000 subjects) and post-marketing surveillance (>4 million prescriptions dispensed worldwide), with serious adverse events occurring in only 1.3% of recipients (similar to 1.2% with placebo) 5. The gastrointestinal effects, while common, are mild and transient, and the neuropsychiatric concerns, while requiring vigilance, have not been definitively linked to the medication in controlled analyses 1, 5.