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Oseltamivir

Posted Aug 19 2009 10:24pm
Oseltamivir is now the blockbuster drug in whole world, including Malaysia.

It is a neuraminidase inhibitor.

The influenze neuraminidase releases newly formed viruses from infected cells, allowing them to spread from cell to cell. This inhibitor mimic the natural substrate of the influenze neuraminidase and bind to the active site, preventing neuraminidase from cleaving host-cell receptors and releasing new virus.

As H1N1 virus attacking Malaysia, out-of-control-ly, nothing preventive can we do now. The last resort is to prescribe (by doctor) and dispense (by pharmacist) oseltamivir (also known as Tamiflu) to those having influenze-like-illness (ILI), especially those having co-morbidities (obesity, diabetes, asthma, etc).

As oseltamivir is being used so extensively, antimicrobial resistance is our concern now.

First, we look at the rational use of oseltamivir.

The sooner the drug is taken after the onset of symptoms (within 48 hours), the better the clinical efficacy (subside of the symptoms in shorter period). If the virus has replicated and infected many cells, the effectiveness of this drug will be severely diminished.

And it should be used in recommended dosage and duration (normally is 75mg twice daily for 5 days; but now the MOH guideline increased the dosing regime up to 150mg twice daily up to 10 days for children more than 12-year-old and more than 40kg).

The over-extensive use of oseltamivir will cause the shortage of supply. That will inspire the sharing of supply, resulting in adequate treatment.

Another problem is the compliance issue. If counselling on this drug is not done appropriately, patients tend to stop taking once the symptoms are gone, regardless the course of treatment already completed, or not (a well-established tendency seen in antibiotic treatment).

The other problem is rather simple: the more you use one antimicrobial on one microorganism, the higher probability the microorganism will develop resistance towards the antimicrobial.

These will lead to the development of oseltamivir-resistance-strain of H1N1 virus.

It's just a matter of when, rather than will it happen or not (there were case of H5N1 virus resistant to oseltamivir already).

We should ensure the proper use of oseltamivir, rather than just providing unlimited supply of it to the public.
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