How Does Tamiflu Work?

Tamiflu is an antiviral drug used in the treatment and prophylaxis of both Influenzavirus A and Influenzavirus B. Like zanamivr, Tamiflu is a neuraminidase inhibitor. It acts as a transition-state analogue inhibitor of influenza neuraminidase, preventing new viruses from emerging from infected cells. Tamiflu is the only neuraminidase inhibitor that has been proven to fight the Bird Flu.

Tamiflu was the first orally active neuraminidase inhibitor commercially developed. It is a considered a prodrug which is hydrolysed hepatically to the active metabolite, the free carboxylate of oseltamivir (GS4071). It was developed by Gilead Sciences and is currently marketed by Hoffmann-La Roche.

There are increasing fears about the potential for a new influenza pandemic around the world. With this new threat, Tamiflu has received substantial media attention. Production capacity is limited, and governments are stockpiling the drug because it has been proven to be effective. The drug has to be prescribed by a doctor and is not given out freely at this point because of supply concerns.

Tamiflu is indicated 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. It is not recommended that it be given to children under one year old. Reports are that it may have an adverse effect on infants under that age.

The usual adult dosage for treatment of influenza is 75 mg twice daily for 5 days, beginning within 2 days of the appearance of symptoms and with decreased doses for children and patients with renal impairment. Tamiflu may be given as a preventive measure either during a community outbreak or following close contact with an infected individual. Standard prophylactic dosage is 75 mg once daily for patients aged 13 and older, which has been shown to be safe and effective for up to six weeks.

It has been suggested that higher doses and longer durations of therapy should be used for treatment of patients with H5N1-type influenza A virus infection (avian influenza). It has been found that the standard recommended dose incompletely suppresses viral replication in at least some patients with H5N1 influenza, rendering therapy ineffective and increasing the risk of viral resistance.

It has been suggested that co-administration of Tamiflu with probenecid could extend the limited supply of Tamiflu. Probenecid reduces renal excretion of the active metabolite of Tamiflu. One study showed that 500 mg of probenicid given every six hours doubled both the peak plasma concentration and the half-life of Tamiflu increasing overall systemic exposure.