From the FDA Drug Label
The efficacy of oseltamivir phosphate in treating influenza has not been demonstrated in patients with influenza symptoms for more than 48 hours [no direct information is provided for 10 days post-symptom onset].
The FDA drug label does not answer the question.
From the Research
I would not recommend giving Tamiflu (oseltamivir) to an 87-year-old patient who tested positive for influenza A but is already 10 days past symptom onset. Antiviral medications like Tamiflu are only effective when started within 48 hours of symptom onset, as stated in various studies 1, 2, 3, 4, 5. After 10 days, the viral replication phase has typically ended, and the patient is likely no longer shedding significant amounts of virus. At this point, the patient's symptoms are more likely due to the inflammatory response rather than ongoing viral activity. Some key points to consider in this scenario include:
- The importance of early treatment with oseltamivir, as emphasized in a study from 1, which highlights that achieving therapeutic concentrations early in the course of the infection greatly impacts the magnitude of benefit.
- The fact that current dosing recommendations for oseltamivir may not be optimal for patients with renal impairment or large body mass, as discussed in 1 and 2.
- The potential for oseltamivir to be used in combination with other treatments, such as baloxavir, in certain cases, as reported in 5. However, these considerations do not change the fact that oseltamivir is not effective when started 10 days after symptom onset. Treatment should instead focus on supportive care to manage any remaining symptoms, such as:
- Acetaminophen for fever or discomfort
- Adequate hydration
- Rest For elderly patients who may have developed complications like secondary bacterial pneumonia, assessment for these complications and appropriate treatment (such as antibiotics if bacterial infection is present) would be more beneficial than starting Tamiflu this late in the course of illness. The reason Tamiflu works only early in infection is that it inhibits the viral neuraminidase enzyme, preventing new virus particles from being released from infected cells—a process that has largely concluded by day 10 of illness.