What are the side effects of Oseltamivir (Tamiflu)?

Side Effects of Oseltamivir (Tamiflu)

The most common side effects of oseltamivir are gastrointestinal symptoms, particularly nausea (10%) and vomiting (9% in adults, 14% in children), which are typically mild and transient. 1

Common Side Effects

• Nausea without vomiting occurs in approximately 10% of patients compared to 6% with placebo 2, 1
• Vomiting occurs in approximately 9% of adults (vs. 3% with placebo) and 14% of children (vs. 8.5% with placebo) 2, 1
• Gastrointestinal symptoms can be reduced by taking oseltamivir with food 2, 1
• Diarrhea is reported in less than 5% of patients 1
• Headache is reported in less than 5% of patients 2, 1
• Dizziness is reported in less than 5% of patients 1

Serious Side Effects

• Transient neuropsychiatric events have been reported during post-marketing surveillance, including: 1
  • Self-injury, delirium, abnormal behavior, hallucinations, agitation, anxiety
  • Altered level of consciousness, confusion, nightmares, and delusions
• The majority of neuropsychiatric event reports were among adolescents and adults in Japan 1, 3
• The FDA advises close monitoring for abnormal behavior in patients receiving oseltamivir 1, 4
• Serious skin and allergic reactions can occur, including: 4
  • Skin rash or hives
  • Blisters or peeling skin
  • Blisters or sores in the mouth
  • Swelling of face, eyes, lips, tongue, or throat
  • Trouble breathing
  • Chest pain or tightness

Special Populations

Children

• Vomiting is more common in children (14%) than adults (9%) 2, 1
• Children may be more susceptible to neuropsychiatric adverse events 3
• Careful attention to dosing is essential for infants, with close monitoring for adverse events 2

Pregnancy

• Oseltamivir is classified as "Pregnancy Category C," indicating no clinical studies have assessed its safety in pregnant women 1
• It should be used during pregnancy only if potential benefit justifies potential risk to the embryo or fetus 1
• No adverse effects have been reported among women who received oseltamivir during pregnancy or among infants born to such women 1

Elderly and High-Risk Patients

• Safety profile is similar to that in healthy adults 5
• No dose adjustment is needed for elderly patients with normal renal function 5

Drug Interactions

• Limited clinical data are available regarding drug interactions with oseltamivir 1
• Potential for interaction exists with other drugs excreted by the anionic pathway via glomerular filtration and tubular secretion 1
• Coadministration with probenecid results in approximately 50% reduced clearance of oseltamivir carboxylate and approximately twofold increase in plasma levels 1
• No impairment of immunologic response to trivalent inactivated influenza vaccine has been demonstrated 1

Monitoring Recommendations

• Monitor all patients, particularly adolescents, closely for abnormal behavior 1, 4
• Neuropsychiatric events generally occur within 48 hours of administration 3
• Stop taking oseltamivir and seek medical help immediately if serious skin or allergic reactions occur 4
• Serious adverse events should be reported to FDA's MedWatch program 1

Dose-Related Side Effects

• Higher doses of oseltamivir (up to 450mg twice daily) show dose-proportional pharmacokinetics without accumulation 6
• Dosage-related events include: 6
  • Nausea (up to 31.3% at higher doses)
  • Vomiting (up to 16.2% at higher doses)
  • Possibly dizziness (up to 11.3% at higher doses)

Taking oseltamivir with food and maintaining adequate hydration can help minimize gastrointestinal side effects while preserving the medication's effectiveness against influenza 1, 5.