When to start Oseltamivir (Tamiflu)?

From the Guidelines

Tamiflu (oseltamivir) should be started as soon as possible after flu symptoms begin, ideally within 48 hours of symptom onset for maximum effectiveness. The standard adult dose is 75 mg twice daily for 5 days, while children's dosing varies by weight, as outlined in the recommendations for prevention and control of influenza in children, 2019-2020 1. Symptoms that warrant treatment include sudden fever, body aches, fatigue, cough, sore throat, and headache. If you suspect you have the flu, contact your healthcare provider immediately for evaluation, as delaying treatment reduces its effectiveness. Tamiflu works by preventing the influenza virus from replicating in your body, which can reduce the duration of illness by 1-2 days and may decrease the severity of symptoms. It can also be prescribed as prevention for high-risk individuals who have been exposed to the flu. Side effects may include nausea and vomiting, which can be reduced by taking the medication with food. Tamiflu is not a substitute for the flu vaccine, which remains the best preventive measure against influenza.

Some key points to consider when deciding when to start Tamiflu include:

• The medication is most effective when started within 48 hours of symptom onset
• Children under 2 years are at an increased risk of hospitalization and complications attributable to influenza
• The FDA has licensed oseltamivir for children as young as 2 weeks
• Treatment should be offered as early as possible without waiting for confirmatory influenza testing for hospitalized children or those at high risk of complications
• Clinical judgment is an important factor in treatment decisions for pediatric patients who present with influenza-like illness

It's also important to note that antiviral resistance to any drug can emerge, necessitating continuous population-based assessment, and that local or national influenza surveillance data should be considered when making treatment decisions 1. Additionally, the CDC recommends that antiviral treatment should be started as soon as possible after illness onset and should not be delayed while waiting for a definitive influenza test result, because early therapy provides the best outcomes 1.

From the FDA Drug Label

Instruct patients to begin treatment with oseltamivir phosphate for oral suspension as soon as possible from the first appearance of flu symptoms, within 48 hours of onset of symptoms. Similarly, instruct patients to start taking oseltamivir phosphate for oral suspension for prevention as soon as possible after exposure [ see Dosage and Administration (2)] The patient should start taking Tamiflu (oseltamivir phosphate) as soon as possible from the first appearance of flu symptoms, within 48 hours of onset of symptoms 2.

From the Research

When to Start Tamiflu

• The decision of when to start Tamiflu (oseltamivir) depends on the timing of symptom onset and the patient's condition 3, 4, 5.
• According to the studies, treatment with oseltamivir is most effective when started within 48 hours of symptom onset 3, 4, 6.
• The benefit of treatment is greatest when antiviral therapy is started within 24 hours of symptom onset 3.
• Starting treatment more than 48 hours after symptom onset may not provide significant benefits in hospitalized general medicine patients or outpatients infected with either H1N1 or other influenza strains 5.
• However, oseltamivir may increase survival when used within five days of symptom onset in influenza H1N1-infected patients who require ICU admission 5.

Patient Factors to Consider

• The effectiveness of oseltamivir may vary depending on the patient's age, with older patients experiencing shorter durations of fever after administration of the first dose 7.
• Patients with influenza A infection may experience shorter durations of fever compared to those with influenza B infection 7.
• The number of biphasic fever episodes may be higher in patients with influenza B infection and in younger patients (aged 0-4 years) 7.