Description

Oseltamivir phosphate (trade name Tamiflu) is an oral antiviral prodrug used to treat and prevent influenza A and B viruses. As a prodrug, it is inactive until it is converted by the body into its active form, oseltamivir carboxylate. It belongs to a class of antiviral drugs known as neuraminidase inhibitors.

Indication

Oseltamivir phosphate is indicated for:

• Treatment of Influenza: It is used to treat acute, uncomplicated influenza in patients (typically 2 weeks of age and older) who have been symptomatic for no more than 48 hours. When started early, it can shorten the duration of flu symptoms and may reduce the risk of complications.

• Prevention of Influenza (Prophylaxis): It can be used to prevent influenza in individuals who are at least 1 year of age and have been in close contact with an infected person. It is not a substitute for the annual flu vaccine. Prophylaxis is generally reserved for high-risk individuals or during a community outbreak.

Mechanism of Action

Oseltamivir’s antiviral effect is achieved by targeting a key enzyme on the surface of the influenza virus called neuraminidase (NA). The mechanism of action involves the following steps:

1. Prodrug Conversion: After oral administration, oseltamivir phosphate is rapidly absorbed and converted by an enzyme in the liver (hepatic esterases) into its active form, oseltamivir carboxylate.

2. Inhibition of Neuraminidase: Oseltamivir carboxylate is a potent and selective inhibitor of the influenza virus neuraminidase enzyme. Neuraminidase is a glycoprotein on the viral surface that plays a critical role in the final stage of the viral replication cycle.

3. Prevention of Viral Release: The primary function of neuraminidase is to cleave sialic acid residues on the surface of infected host cells. This cleavage is necessary for newly formed viral particles to be released from the infected cell and to spread to other cells. By inhibiting neuraminidase, oseltamivir carboxylate prevents the release of these new viruses. The new viral particles become “stuck” to the surface of the infected cell, preventing them from infecting other cells and halting the spread of the infection within the body.

This mechanism effectively reduces the viral load and the severity and duration of influenza symptoms. The effectiveness of oseltamivir is highly dependent on timely administration, as it works best when started within 48 hours of the onset of symptoms.