indication

Oseltamivir (Tamiflu) is for the treatment of uncomplicated acute illness due to influenza infection in patients 1 year and older who have been symptomatic for no more than 2 days. It is also used for the prophylaxis of influenza in adult patients and adolescents 13 years and older.

pharmacology

Oseltamivir is an antiviral drug, a neuraminidase inhibitor used in the treatment and prophylaxis of both influenza A and influenza B. Oseltamivir is a prodrug (usually administered as phosphate), it is hydrolysed hepatically to the active metabolite, the free carboxylate of oseltamivir (GS4071). Like zanamivir, oseltamivir acts as a transition-state analogue inhibitor of influenza neuraminidase.

mechanism of action

Oseltamivir is an ethyl ester prodrug requiring ester hydrolysis for conversion to the active form, oseltamivir carboxylate. The proposed mechanism of action of oseltamivir is inhibition of influenza virus neuraminidase with the possibility of alteration of virus particle aggregation and release.

toxicity

At present, there has been no experience with overdose. Single doses of up to 1000 mg of oseltamivir have been associated with nausea and/or vomiting. Mean LD (intravenous, mouse) = 100 mg/kg.

biotransformation

Extensively converted to oseltamivir carboxylate by esterases located predominantly in the liver. Neither oseltamivir nor oseltamivir carboxylate is a substrate for, or inhibitor of, cytochrome P450 isoforms. At least 75% of an oral dose reaches the systemic circulation as oseltamivir carboxylate.

absorption

Readily absorbed from the gastrointestinal tract after oral administration with a bioavailability of 75%.

half life

1 to 3 hours in most subjects after oral administration.

route of elimination

Absorbed oseltamivir is primarily (>90%) eliminated by conversion to oseltamivir carboxylate. Oseltamivir carboxylate is not further metabolized and is eliminated in the urine. Oseltamivir carboxylate is eliminated entirely (>99%) by renal excretion.