What are the adverse effects of oseltamivir (Tamiflu)?

Adverse Effects of Oseltamivir (Tamiflu)

The most common adverse effects of oseltamivir are gastrointestinal symptoms, particularly nausea (10%) and vomiting (8-9%), which are typically mild, transient, and can be reduced by taking the medication with food. 1

Common Adverse Effects

• Gastrointestinal effects:

  • Nausea without vomiting: approximately 10% (vs. 6% with placebo) 1
  • Vomiting: approximately 9% in adults (vs. 3% with placebo) and 14% in children (vs. 8.5% with placebo) 1
  • Diarrhea: reported in <5% of patients 1
  • These symptoms typically occur on the first or second day of treatment and resolve spontaneously within 1-2 days 1
  • Taking oseltamivir with food may reduce the severity of nausea and vomiting 1

• Neurological effects:

  • Headache: reported in 2% of treatment patients and 17% of prophylaxis patients 2
  • Dizziness: reported in <5% of patients 1

• General symptoms:

  • Pain: reported in 4% of prophylaxis patients (vs. 3% with placebo) 2

Serious Adverse Effects

• Neuropsychiatric events:

  • Transient neuropsychiatric events including self-injury, delirium, abnormal behavior, hallucinations, agitation, anxiety, altered level of consciousness, confusion, nightmares, and delusions have been reported during post-marketing surveillance 1
  • The majority of these reports were among adolescents and adults in Japan 1
  • FDA advises close monitoring for abnormal behavior in patients receiving oseltamivir 1

• Skin and hypersensitivity reactions:

  • Allergic reactions including oropharyngeal or facial edema 1
  • Rash, dermatitis, urticaria, eczema 2
  • Rare but serious skin reactions including toxic epidermal necrolysis, Stevens-Johnson Syndrome, and erythema multiforme 2

• Other serious adverse events reported during post-marketing surveillance:

  • Cardiac disorders: arrhythmia, QT prolongation 2, 3
  • Hepatobiliary disorders: hepatitis, abnormal liver function tests 2
  • Nervous system disorders: seizures 2
  • Metabolic disorders: aggravation of diabetes, hyperglycemia 2, 3
  • Gastrointestinal bleeding, hemorrhagic colitis 2

Special Populations

• Children:

  • Vomiting is the most common adverse effect in children (14% vs. 8.5% with placebo) 1
  • In children aged 2 weeks to less than 1 year, vomiting (9%), diarrhea (7%), and diaper rash (7%) were most frequently reported 2

• Pregnancy:

  • Oseltamivir is classified as "Pregnancy Category C," indicating no clinical studies have assessed its safety in pregnant women 1
  • 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

• Patients with hereditary fructose intolerance:

  • One dose of 75 mg oseltamivir delivers 2 grams of sorbitol, which is above the daily maximum limit for patients with hereditary fructose intolerance and may cause dyspepsia and diarrhea 2

Drug Interactions

• Limited clinical data are available regarding drug interactions with oseltamivir 1
• Potential for interaction 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

Compliance Considerations

• In a school outbreak setting, 41% of pupils and 47% of staff reported adverse effects from oseltamivir 4
• 14% of pupils and 20% of staff did not complete the prescribed course, primarily due to adverse effects 4
• Nausea, vomiting, and rash were significantly associated with failure to complete the course 4

Monitoring Recommendations

• Monitor patients closely for abnormal behavior, particularly adolescents 1
• Serious adverse events should be reported to FDA's MedWatch program 1
• Be alert to potential secondary bacterial infections and treat them appropriately, as oseltamivir has not been shown to prevent such complications 2