Oseltamivir appears to be more effective against influenza A/H3N2 in a severely ill population than it is against A/H1N1 or influenza B but early treatment is essential.
A Greek study of 1,330 patients admitted to intensive care or mechanically ventilated for laboratory confirmed influenza found early administration of oseltamivir could reduce mortality by about 30% in patients affected by A/H3N2.
Only 27% of all patients received oseltamivir within 48 hours of symptom onset but most (87%) were treated with the neuraminidase inhibitor by or at the time of ICU admission.
The study found the mortality rate was a high 46.8% overall and did not different significantly based on influenza type or early versus late treatment with oseltamivir.
“However, among patients with influenza A/H3N2, fewer patients died among the early oseltamivir group compared to the late oseltamivir group (33.7% vs 48.4% respectively, p=0.029), the study authors wrote.
“Median length of stay in the ICU was also shorter in the early treatment group (12 days vs 15 days, p=0.003).”
The researchers said the fact that oseltamivir effectiveness may vary between different influenza types was ‘likely due to differences in the structure and activity of viral neuraminidase’ and highlighted the importance of more research for seasonal influenza management and future pandemic planning.
Commenting on the study, Professor Peter Wark from the Priority Research Centre for Asthma and Respiratory Disease told the limbic while the non-randomised observational study had some limitations, its findings were relevant to Australia.
And the key message was to instigate early anti-viral treatment especially in the middle of ‘flu seasons and in at-risk populations such as the elderly.
“Nobody really knows what the time frame should be in the context of someone with community acquired pneumonia (CAP). However the thought is the sooner you can start treatment for a primary influenza pneumonia, the better.”
“And the only way around that given the constraints of having to make a positive diagnosis – in most health institutions that is not something that is going to be able to happen in 24-48 hours – if the context is right and you are concerned about influenza, is really to treat empirically for it and await results.”
“You can’t do a swab and have that result immediately in terms of PCR unless you are going down the route of another point-of-care test. But at the moment, most hospitals throughout Australia are relying on PCR confirmation and that delays the ability to initiate treatment.”
“If you are seriously concerned that influenza is the cause of severe CAP then you have to treatment it empirically.”