The Medical Post is pleased to feature Corridor consults: expert answers to your clinical questions. Many of our readers tell us that in this rapidly changing medical world they no longer have the opportunity to discuss issues and questions with their peers in hallway chats. So send your questions to us, and we'll answer them in an upcoming issue of Medical Post. E-mail your clinical questions to Medical Post writer-editor andrew.skelly@medicalpost.rogers.com.

Experts address antiviral’s role in H1N1 treatment (Back to the top)

1. As we all wait to see what degree of havoc H1N1 will wreak this fall, I have begun to wonder about the utility of oseltamivir (Tamiflu). I am accustomed to prescribing it to reduce the duration and severity of influenza A and B symptomatology, but I’ve read nothing about its effectiveness with respect to pneumonia and respiratory failure in H1N1 infection. Is it useful?—Dr. Mary Taylor, Ottawa

2. When oseltamivir first became available to treat influenza A, the benefit was thought to be modest, at best. Also, I seem to recall that only four out of five infected patients would respond. Why is oseltamivir now perceived to be so important?—Dr. Mark Berner, Montreal

These two questions are more complex than they may appear on first read. Influenza in general causes severe illness and death through one of three mechanisms:

1) direct viral invasion of the lung leading to severe viral pneumonia with acute respiratory distress syndrome;

2) bacterial superinfection due to pneumococcus, staphylococcus or meningococcus; and

3) clinical decompensation in patients with severe underlying conditions such as the elderly or those with chronic illnesses such as diabetes and chronic obstructive pulmonary disease (COPD).

So far, severe H1N1 disease in previously healthy young people has occurred by the first mechanism (direct invasion). It appears to occur more frequently than we have seen with seasonal influenza. Oseltamivir is an important tool for fighting severe viral illness where there is direct invasion of the lung.

For severe influenza caused by the second and third mechanisms, antibiotic treatment (for bacterial infection) and attention to managing the underlying disease (heart disease, COPD, etc.) will be most important, although oseltamivir may play some role in limiting the illness. Of note, the last mechanism is the most common cause of severe illness in seasonal influenza.

For the majority of cases of H1N1 seen in the community, the illness has been mild and oseltamivir therapy is not indicated, nor is it of much value in changing the clinical course of a mild infection. Furthermore, overuse of oseltamivir may spur the development of resistance, leading to even more problems for treatment of those with severe disease due to H1N1 viral invasion.

Got a clinical question? E-mail it to the editor of the Medical Post:andrew.skelly@medicalpost.rogers.com; subject line “Corridor Consults.”