VAIL, COLO. — The recommended antiviral therapy during the coming influenza season will depend on whether a patient has laboratory-confirmed novel influenza A(H1N1).
In patients with confirmed novel influenza A(H1N1), or in patients with laboratory-confirmed influenza A(H3N2) or B, the first-line antiviral is oseltamivir (Tamiflu). However, in patients with a positive laboratory test for influenza A or seasonal A(H1N1), the preferred agent is zanamivir (Relenza), according to Centers for Disease Control and Prevention recommendations based on antiviral resistance patterns.
Zanamivir is also the first-line agent in patients who are suspected of having influenza on clinical grounds but who did not have laboratory tests or had negative results, Dr. Adriana Weinberg explained at a conference on pediatric infectious diseases sponsored by the Children's Hospital in Denver.
Novel H1N1, A(H3N2), and B viruses share the same antiviral susceptibility pattern—all are susceptible to both zanamivir and oseltamivir. However, oseltamivir is preferred because as an oral agent it is easier to administer than the inhalation powder zanamivir, has fewer side effects, and is approved for use across a wider age range, added Dr. Weinberg, professor of pediatrics and medicine and medical director of the clinical virology laboratory at University of Colorado Hospital, Anschutz.
The recommended alternative to zanamivir in patients with laboratory evidence of influenza A, a negative test result, or no testing is the combination of oseltamivir plus rimantadine (Flumadine). For patients who are positive for seasonal influenza A(H1N1), the fallback antiviral regimen is rimantadine alone.
Alternatives to the inhalation-only zanamivir are important because that administration route is problematic in patients who are intubated or have asthma or other airway disease. Plus, zanamivir is not approved for use in children younger than age 7 years, she noted. In contrast, on April 28 the Food and Drug Administration approved a 1-year Emergency Use Authorization for the use of oseltamivir for treatment and prophylaxis in infants.
A big concern among virologists and infectious disease specialists is that the novel H1N1 virus will become resistant to oseltamivir, as did seasonal A(H1N1). An investigational antiviral agent that could prove particularly valuable is an intravenous formulation of zanamivir, a drug still active against all strains of influenza. Another promising drug is peramivir, a neuraminidase inhibitor that appears to be effective and well tolerated. Its big advantage is it can be administered parenterally, Dr. Weinberg noted.
This Month's Talk Back Question
What has your practice done to prepare for the spread of the novel influenza A(H1N1) virus?