The timely detection of influenza in at-risk patients is important to prevent hospital-based transmission and influenza-associated morbidity and mortality. Guidelines issued by professional associations and public health agencies need to be translated into everyday clinical practice, thus antiviral therapy should be initiated early and monitored closely.
The effectiveness of oseltamivir (known under the brand name Tamiflu) in the treatment of influenza infections has been demonstrated in a range of clinical studies. The key benefits of the therapy are earlier resolution of illness combined with earlier return to usual health and ability to carry out everyday activities. It is also used for prophylaxis of influenza in patients older than one year.
Use for treatment
When administered to healthy adults with naturally acquired influenza infection, oseltamivir (in a dose of 75 mg twice daily for five days) can reduce the duration of the disease by up to 1-2 days and the severity of illness by up to 40% (if the treatment is initiated within 36 hours of the onset of symptoms).
Earlier administration of this drug has been shown to reduce the symptom severity, fever duration and the time to return to baseline activity. It must be added that the initiation of therapy within the first 12-24 hours after the onset of fever markedly reduces the median duration of illness than when therapy is initiated at 48 hours.
Despite the lack of convincing data regarding the efficacy of oseltamivir in preventing complications of influenza, medical literature suggests it may be useful for unvaccinated individuals who are at high risk of infection and severe complications. Clear evidence exists that oseltamivir treatment leads to a reduction in secondary lower respiratory tract complications (such as bronchitis and pneumonia).
Use for prophylaxis
Oseltamivir can be used in short-term prophylaxis of vulnerable persons when the risk of contracting influenza virus infection is high. Prophylactic use of oseltamivir results in a reduced risk of developing influenza by up to 90%, whereas the number of infections and infection-related respiratory illness is also lower.
The use of oseltamivir post-exposure prophylaxis is more cost-effective than amantadine prophylaxis or no prophylaxis at all. Although this drug is registered as prophylaxis for up to 42 days, certain studies have demonstrated good tolerability of supervised oseltamivir administration for 16 weeks.
Furthermore, targeted prophylaxis of oseltamivir is useful in containing an outbreak of influenza at mass gatherings. A combination of case treatments and ring prophylaxis of contacts seems to be a viable and economically sustainable strategy. Further research needs to be directed to certain doubts over oseltamivir’s place in such type of influenza control (i.e. how, when and for whom oseltamivir should be used).
Use in children, elderly and pregnant women
Studies in children have shown that oseltamivir treatment reduces the median duration of illness by 36 hours, but also decreases the incidence of associated otitis media. Its use has been associated with reduced risks of influenza-related complications and hospitalizations in high-risk children and adolescents. In addition, the drug is well-tolerated among asthmatic children.
Oseltamivir usage is associated with a 92% reduction in the incidence of laboratory-confirmed clinical influenza in frail, elderly people living in homes for seniors. Simultaneous treatment and prophylaxis with oseltamivir has been successfully used to control influenza A and B outbreaks in elderly nursing home populations.
Even though oseltamivir is classified as category C drug in pregnancy, transplacental transfer of metabolites appears to be low and the incidence of adverse maternal or fetal outcomes not higher than background rates. Nevertheless, clinicians who use oseltamivir in pregnant women should consider that the pharmacokinetics of the active metabolite of oseltamivir is affected by pregnancy.