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Treatment of seasonal influenza in adults

INTRODUCTION

Seasonal influenza is an acute respiratory illness caused by influenza A or B viruses. Influenza occurs in outbreaks and epidemics worldwide, mainly during the winter season. Although acutely debilitating, influenza is usually a self-limited infection; however, it is associated with increased morbidity and mortality in certain high risk populations.

Two classes of antiviral drugs are available for the treatment and prevention of influenza [1-3]:

  • The neuraminidase inhibitors zanamivir and oseltamivir, which are active against both influenza A and B.
  • The adamantanes, amantadine and rimantadine, which are only active against influenza A [2]. Due to a marked increase in resistant isolates, the ACIP recommends that adamantanes not be used in the United States for the treatment of influenza, except in selected circumstances [1]. (See 'Choice of antiviral drug' below.)

The role of these drugs in the treatment of influenza will be reviewed here. Their role in the prevention of seasonal influenza, treatment and prevention of swine H1N1 influenza and avian influenza, and treatment and prevention of influenza in children are discussed separately; the pharmacologic characteristics of the antiviral drugs are also presented elsewhere . (See "Prevention of seasonal influenza in adults" and "Treatment of pandemic H1N1 influenza ('swine influenza')" and "Prevention of pandemic H1N1 influenza ('swine influenza')" and "Treatment and prevention of avian influenza" and "Antiviral drugs for the prevention and treatment of influenza in children" and "Pharmacology of antiviral drugs for influenza".)

BENEFITS OF THERAPY

When initiated promptly, antiviral therapy can shorten the duration of influenza symptoms by one to three days; the benefit is greatest when given within the first 24 to 30 hours and in patients with fever at presentation [1,4-8]. Little to no benefit has been demonstrated when treatment is initiated two days or more after the onset of uncomplicated influenza. However, a patient survey found that only 13 percent of patients called their physician within 48 hours of the onset of influenza-like symptoms [9].
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