WASHINGTON – The government approved sale of a second pill to treat erectile dysfunction Tuesday, setting the stage for a fierce battle with Viagra in the billion-dollar-plus impotence market.

The new drug, Levitra, is in the same family as Viagra. Both work by targeting an enzyme important for maintaining an erection. The Food and Drug Administration approved Levitra on Tuesday.

Until now, the blue, diamond-shaped Viagra pills have been the only oral prescription drug available for an estimated 30 million American men who suffer some degree of impotence – most of whom don’t seek medical therapy.

Levitra, made by Bayer AG and marketed by GlaxoSmithKline, recently began selling in Europe. A third impotence pill – Cialis, from Eli Lilly & Co. and Icos Corp. – also has European approval and is expected to hit U.S. pharmacies later this year.