Pharmacology of Oseltamivir phosphate.

Oseltamivir is an ethyl ester prodrug which requires conversion to the corresponding carboxylate to be physiologically active. The proposed mechanism of action is that oseltamivir inhibits the neuraminidase protein on the viral surface and interferes with virus particle aggregation and release. A nice simple flash animation of oseltamivir can be found via the following link: Oseltamivir flash program. (Requires flash software)

Oseltamivir phosphate has been proved to be effective against influenza A and B types. It is administered ether as a 75mg oral capsule or as a powder suspension, twice daily for approximately 5 days depending on severity of infection. It has shown minor adverse effects such as tiredness, Diarrhoea and rash. It has been proved to be more than 85% effective than a placebo trial.

Mean (% CV) Pharmacokinetic Parameters of Oseltamivir and Oseltamivir Carboxylate After a Multiple 75 mg Capsule Twice Daily Oral Dose (n=20)

Parameter
Oseltamivir
Oseltamivir
Carboxylate
Cmax (ng/mL)
65.2 (26)
348 (18)
AUC0-12h (ngh/mL)
112 (25)
2719 (20)

The above table shows basic pharmokinetic data for the distribution of the inactive and active form of Oseltamivir in the blood plasma during a typical day of treatment (two 75mg oral capsules) The Cmax is a representation of the peak plasma concentration, it clearly shows that the active form is more easily absorbed into the blood than the inactive form. The second parameter is the area under the curve of a concentration-time graph for both forms. Oseltamivir Carboxylate is over 20X more widely distributed and persistent than the inactive Oseltamivir free base. On comparison to other commonly used antiviral drugs used in influenza treatment such as zanamivir, The Cmax and AUC are higher for the active form of Oseltamivir then any other commonly used anti influenza drug. This implies the effectiveness of this drug should be higher, this claim reflects that in 2004 Tamiflu was the worlds number one prescribed antiflu drug.

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