How long after you have taken Tamiflu is it still effective?

Can taking Tamiflu as a preventive make you resistant to the drug if it is taken later?

• Answer:

  No. The resistance would be the resistance of the virus to the Tamiflu, not your resistance to Tamiflu (Oseltamivir). There have been some but very few cases of strains of 2009 H1N1 Pandemic Swine Flu that are resistant to Tamilfu. This can happen when there is mass use of the drug in an area to prevent infection, or when someone taking the drug does not take it regularly or as long as prescribed, which allows the virus to learn how to mutate to be resistant. According to the CDC: Antiviral Resistance Oseltamivir resistance appears to be rare at this time. However, oseltamivir-resistant 2009 H1N1 viruses have been identified, typically among persons who develop illness while receiving oseltamivir for chemoprophylaxis or immunocompromised patients with influenza who are being treated. These findings underscore the importance of careful and limited use of antiviral medications for chemoprophylaxis and the need for persons taking antiviral medications to continue to follow recommendations for hand and respiratory hygiene to prevent the spread of antiviral resistant viruses. Additional information on oseltamivir resistance among 2009 H1N1 viruses is available at http://www.cdc.gov/h1n1flu/HAN/070909.htm. Monitoring for antiviral resistance is ongoing and clinicians and state health departments should continue to follow state and national guidance for submission and testing of clinical specimens from persons with suspected 2009 H1N1 virus infection, particularly from those who develop influenza while taking chemoprophylaxis or who have prolonged viral shedding while on treatment.