Tamiflu is designed for the treatment of infections due to influenza A and B virus in people at least one year of age, and prevention of influenza in people at least 1 year or older. Adult dosage for treatment of influenza is normally 75 mg twice daily for 5 days, starting within 2 days of the appearance of symptoms children and patients with kidney problems should be given reduced doses. Oseltamivir may be given as a preventive measure either during a community outbreak or following close contact with an infected individual. The standard prophylactic dose is 75 mg once daily for patients aged 13 and older, which would be safe and effective for up to six weeks. 

For treatment of patients with H5N1-type influenza A virus infection (avian influenza) higher doses over a longer period should be given. It has been found that the standard recommended dose does not suppress viral replication in at least some patients with H5N1 influenza, rendering medication ineffective and increasing the risk of viral resistance.

Administering Oseltamivir with Probenecid could extend the limited supply of Tamiflu. Probenecid reduces renal excretion of the active metabolite of Tamiflu. Studies have shown s that 500 mg of Probenecid given every six hours doubled both the peak plasma concentration and the half-life of Oseltamivir, increasing overall systemic exposure by 2.5-fold. Whilst the evidence for this interaction comes from a study by Roche, it was publicised in October 2005 by a doctor who had reviewed the data. Probenecid was used in similar fashion during World War II to extend limited supplies of penicillin, and is still currently used to increase penicillin concentrations in serious infections.

Tamiflu is marketed by Gilead as capsules containing oseltamivir phosphate 98.5 mg equivalent to oseltamivir 75 mg and as a powder for oral suspension containing oseltamivir phosphate equivalent to oseltamivir 12 mg/ml.

Common adverse drug reactions associated with oseltamivir medication include: nausea, vomiting, diarrhoea, abdominal pain, and headache. Rare drug reactions include: hepatitis and elevated liver enzymes, rash, allergic reactions including anaphylaxis, and Stevens-Johnson syndrome.

Other associated drug reactions have been reported in pos marketing surveillance including: toxic epidermal necrolysis, cardiac arrhythmia, seizure, confusion, aggravation of diabetes, and haemorrhagic colitis.

As a prescription drug check with your doctor about interactions with other drugs you may be taking. Some pre-existing health issues may also affect the way this drug interacts with you. Talk to your doctor when considering a new drug and be open and honest.