GlaxoSmithKline has been given a green light from European regulators in 15 European Union countries to sell its antiviral drug Relenza (zanamivir) for the prevention of influenza in adults and children from the age of five.

The drug was previously cleared for the treatment of flu in patients aged 12 and above, and regulators have now also extended Relenza’s reach in this setting, allowing treatment from the age of five.

“This approval is a significant step forward as it provides the medical community in Europe with another option to prevent and treat seasonal influenza enabling governments to prepare for a potential flu pandemic,” noted David Stout, president of pharmaceutical operations at the firm.

But Relenza has, so far, failed to become the blockbuster GSK once hoped. Although its profile was raised in the wake of the anticipated bird flu pandemic, with governments looking to stockpile the drug, demand never matched that of rival Roche's Tamiflu (oseltamivir) - an oral offering from the same neuraminidase inhibitor class.

The drug was launched globally in 1999 and 2000. But, in 2001, GSK's chief executive Jean-Pierre Garnier dismissed Relenza as a non-priority product after poor sales results. And last year, Australia's Biota Holdings, which developed the drug and is entitled to 7% of GSK’s Relenza sales, said it is seeking damages of A$308-430 million (US$234-326 million) from the firm, claiming that the UK giant failed to sufficiently promote and support the drug.

Biota said Relenza had been "effectively abandoned at birth" and, having captured some 50% of the $330 million global market for flu drugs, saw this whittled away to just 3% over the following years. The litigation is still ongoing, a spokesperson for GSK told PharmaTimes World News.