Singapore, March 6, 2008: Physicians from countries affected by the deadly H5N1 influenza virus (bird or avian flu) have presented case reports about antiviral use in patients infected with H5N1, including treatment with the oral antiviral Tamiflu (oseltamivir). The physicians' reports were revealed at the International Symposium on Respiratory Viral Infections (ISRVI), February 28–March 2, 2008 in Singapore.

 

In Indonesia, of the total of 119 H5N1 human cases reported, 22 survived – an 18 percent survival rate overall. Of the 119, 33 patients received no Tamiflu, all of whom died. Tamiflu was administered to the other 86 patients, with a 26 per cent survival rate overall.

 

Recent information about eight Vietnamese patients infected with H5N1 was also presented. All eight patients received Tamiflu, however, all eight patients presented to the hospital later than five days after onset of illness. Only three of the eight patients survived reinforcing that treatment benefit is reduced for patients that receive the drug later in the course of illness. In two patients who were unable to take the drug orally due to the severity of their illness, physicians administered the drug by nasogastric tube and found it was well absorbed and there was a reduction in H5N1 virus in these patients.

 

The clinical findings, supported by animal data, are also presented at ISRVI, which shows that oseltamivir treatment was effective against H5N1 influenza viruses representing different clades/subclades. However, higher doses were required for the more pathogenic H5N1 viruses. Study author Dr Elena Govorkova, St Jude Children's Research Hospital, Memphis, US, said, multiple factors can affect the susceptibility of antiviral therapy with highly pathogenic H5N1 influenza viruses and it is reassuring that oseltamivir, in mouse models, demonstrates activity even to the most pathogenic circulating strains.

 

Data also confirms the low level of resistance reported with Tamiflu to H5N1 avian influenza in the field; there are only five cases of published reports of H5N1 resistance or reduced susceptibility to Tamiflu. Laboratory results have shown 96 percent of H5N1 strains (53 out of 55) tested in the laboratory were sensitive to Tamiflu.

 

This compares to the around 14 per cent of isolates tested this year of the seasonal influenza A H1N1 virus showing resistance to Tamiflu, reported at the conference. It is important to note that these increased levels of resistance have only been reported spontaneously in this year's H1N1 (Solomon Islands) seasonal strain, and not an avian strain such as H5N1, and not in patients who have been administered Tamiflu.