US gum giant Wm. Wrigley Jr. has been granted US government patent 6,531,114 for a gum that delivers sildenafil citrate, the active ingredient found in Viagra.

However, Viagra manufacturer Pfizer will hold the patent to Viagra for another eight years, so the gum group has no plans to market such a product in the short term.

"There's been no development activity whatsoever nor is any anticipated at present," Christopher Perille, a Wrigley spokesman, is quoted as saying by the Financial Times. He did not rule out the possibility that Chicago-based Wrigley might reconsider that decision when Pfizer's Viagra patent runs out.

Despite the success of gum that helps smokers quit, such as Nicorette, the delivery of drugs through gum has not taken off in the medical world, as it is not a reliable way of releasing a known quantity of medicine. The amount of drug released over a period is dependant on how fast and long the gum is chewed for, resulting in dosage intakes that are not easily measured. However, chewing causes the drug to be released into the blood stream through the mouth, making it potentially less irritable on the stomach.

Apparently it would have to be chewed for at least two minutes about 30 minutes before sex, indicating a similar time frame to the little blue pills used today.

Last year, Viagra had global sales of US$1.7bn, forecast to rise to $1.9bn this year. Once Pfizer's patent expires we are likely to see a huge amount of NPD activity in the sector. In fact, Viagra is soon to encounter competition for the first time. Germany's Bayer and GlaxoSmithKline of the UK are expected to gain approval for Levitra some time this year, reported the FT. US pharmaceuticals group Eli Lilly and partner Icos also expect US approval for another male impotence drug Cialis late this year.

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