The FDA, which had already approved Relenza (zanamivir for inhalation) for treatment of seasonal flu, has okayed it for prevention as well in adults and children age five or older.

The agency’s action made Relenza, marketed by GlaxoSmithKline, the second antiviral approved for both prevention and treatment of influenza A and B. Tamiflu (oseltamivir) was already approved for both indications.

In announcing the approval, the FDA cautioned that Relenza is “not a substitute for the flu vaccine, which is the primary means for preventing influenza.”

The FDA said Relenza demonstrated efficacy in preventing seasonal influenza in four large placebo controlled studies. In two of these trials, just over 4% of households taking Relenza developed flu symptoms compared with 19% of households randomized to placebo.

The other two trials tested the drug in communities experiencing a flu outbreak. In one of these studies the drug was tested in adults ages 18 or older. In that study 2% of patients randomized to Relenza developed influenza symptoms versus 6.1% of patients in the placebo arm.

The other community-based study enrolled people ages 12 to 94, with 56% of participants over age 65. Only 0.2% of volunteers randomized to Relenza developed flu symptoms compared with 1.4% of the placebo group.

In adults and adolescents the most common adverse effects associated with Relenza were headaches, diarrhea, nausea, vomiting, nasal irritations, bronchitis, cough, sinus infections, ear, nose and throat infections and dizziness. Among children the most common adverse effects were ear, nose, and throat infections; vomiting; and diarrhea. Less common reported events included rashes and allergic reactions, some of which were severe.

Reports of bronchospasm, including deaths, were reported in some patients after the initial approval of Relenza. Most of these patients had asthma or chronic obstructive pulmonary disease. Relenza therefore was not recommended for treatment or prophylaxis of seasonal influenza in individuals with underlying airway diseases such as asthma or chronic obstructive pulmonary disease.

Relenza was not recommended for prevention of influenza among people in nursing homes.