Four antivirals not suitable for routine seasonal influenza control

EMBARGO: 00:01H (London time) Thursday January 19, 2006. In North America the embargo lifts at 18:30H ET Wednesday January 18, 2006.

The commonly prescribed antiviral medications amantadine and rimantidine should not be used for seasonal or pandemic influenza control because they are ineffective and can cause adverse side-effects, according to a study published online today (Thursday January 19, 2006) by The Lancet. Another two antivirals--zanamivir and oseltamivir--should not routinely be used for seasonal influenza control and should only be used in a serious epidemic or pandemic alongside other public health measures, state the authors. The researchers also found no evidence that zanamivir (Relenza) and oseltamivir (Tamiflu) were effective against avian influenza.

The news follows the recent interim recommendations from the US Centres of Disease Control (CDC) that neither amantadine or rimantadine should be used for the treatment or prevention of influenza A in the US for the remainder of the 2005-2006 influenza season because of growing resistance to the drugs. The CDC instead recommends the use of zanamivir or oseltamivir for treatment or prevention.

Tom Jefferson (Cochrane Vaccines Field) and colleagues combined data from 50 trials on two classes of drugs, the M2 ion channel inhibitors, amantadine and rimantadine, and the newer neuraminidase inhibitors zanamivir and oseltamivir. They found that while both classes of antivirals prevented or eased symptoms of influenza they did not prevent infection. They also found that neither class of antivirals could effectively treat influenza-like illnesses. Influenza is caused by influenza A and B viruses, whereas influenza-like illness is caused by scores of different viruses, not all of which are influenza. In practice, influenza like-illness is what doctorsdiagnose prior to testing for specific types of influenza.

Another finding was that the neuraminidase inhibitors did not stop virus shedding from the nose (an important mechanism for influenza spread) but did diminish the effect. The M2 ion channel blockers did not have an effect on viral shedding. The investigators also found that the use of amantadine quickly led to the emergence of resistant viral strains and both amantadine and rimantadine caused unpleasant adverse effects, such as hallucinations.

Dr Jefferson states: "The use of amantadine and rimantadine should be discouraged. Because of their low effectiveness, neuramidase inhibitors should not be used in seasonal influenza control and should only be used in a serious epidemic or pandemic alongside other public-health measures such as use of masks, gowns, gloves, quarantine, and hand washing." (Quote by e-mail; does not appear in the published paper)

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Contact: Dr Tom Jefferson, Cochrane Vaccines Field. Via Adige 28a, 00061 Anguillara Sabazia, Roma, Italy. T) 39-069-990-0989 /39-329-202-5051 (mobile) toj1@aol.com


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