For what purposes can anti-viral drugs be used against influenza A (H1N1)?
So far most people who have contracted the new Influenza A (H1N1) virus have experienced influenza-like symptoms (such as sore throat, cough, runny nose, fever, malaise, headache, joint/muscle pain) and recovered without antiviral treatment.
Anti-viral drugs may reduce the symptoms and duration of illness, just as they do for seasonal influenza. They also may contribute to preventing severe disease and death. Influenza A (H1N1) is a new virus and only a small number of people with the infection have been treated for it with anti-viral drugs. WHO is in touch with public health authorities and clinicians in affected countries and is gathering information about how effective the drugs are.
To which antiviral drugs does this H1N1 influenza virus respond?
There are two classes of anti-viral drugs for influenza: inhibitors of neuraminidase such as oseltamivir (Tamiflu) and zanamivir (Relenza); and adamantanes, such as amantadine and rimantadine. Tests on viruses obtained from patients in Mexico and the United States have indicated that current new H1N1 viruses are sensitive to neuraminidase inhibitors, but that the viruses are resistant to the other class, the adamantanes.
Could the virus become resistant to oseltamivir and zanamivir?
Resistance can develop to antiviral drugs used for influenza. Therefore, WHO and its partners are monitoring anti-viral drug resistance. MOH has advised that Tamiflu and Relenza are to be reserved for treatment of cases to minimize the risk of the virus acquiring resistance through inappropriate usage of the medication.
Under what circumstances should anti-viral drugs be administered?
The anti-viral drugs are to be administered when there is confirmation of an infection. They can be used for prophylaxis to prevent infection during a pandemic or it can be issued as post-exposure prophylaxis after a person is exposed in close proximity to a patient with confirmed infection. Prophylaxis can also be provided for travel to high risk affected areas, however MOH has advised against unnecessary travels to these areas. MOH has reserved anti-viral medication to provide prophylaxis for essential services such as healthcare personnel in the event of a pandemic influenza.
Treatment should be initiated within 48 hrs of onset of symptoms and consist of one 75 mg capsule twice a day for 5 days. Prophylaxis consists of one 75mg capsule once per day for up to 6 weeks. Prophylaxis of close contacts will be implemented during the early phase of outbreak in order to slow down the spread of disease. Protection stops when prophylaxis is terminated. Oseltamivir is well tolerated with minimal side-effects. Most common side effects are nausea and vomiting.
Which drug will be provided, and how much of it do WHO and MOH have available?
WHO had a global stockpile of approximately 5 million adult treatment courses of oseltamivir. Part of this stockpile has already been distributed through the WHO Regional Offices, which are handling allocation and distribution. WHO is currently distributing the remaining 3 million adult treatment courses of this stockpile to developing countries in need.
WHO continues to assess needs and to work with manufacturers to secure more donations of anti-virals. More anti-viral drugs will be distributed once these donations are received.
MOH have a stockpile of enough medication for treatment of ¼ of the population based on an influenza attack rate of 25%.