Levitra is being manufactured by the German firm, Bayer AG, and marketed by the British firm GlaxoSmithKline (GSK).

The August 19, 2003, FDA approval of Levitra was based on more than 50 trials involving more than 5,700 men. The studies suggested that men who took the pill were on average five times more likely to achieve an erection suitable for intercourse when compared with those given an inactive substance known as a placebo.

A third anti-impotence pill, Cialis® (tadalafil), which is being developed by Eli Lilly and Co. and ICOS Corp., is anticipated to reach the U.S. market later this year.

Levitra, Viagra, and Cialis all work by blocking an enzyme called PDE-5, which affects blood flow to the penis. But the potency, speed, and duration of each drug are hotly disputed. Levitra's makers say its major advantage is that it works quickly: Men taking Levitra may have an erection in 16 minutes, and any time after that, up to five hours later. Studies of Viagra show half of men taking the drug were able to have sex within 20 minutes

The FDA warned that, like Viagra, Levitra should not be used by patients who have had a recent heart attack, stroke, or who have very low blood pressure or uncontrolled high blood pressure. For otherwise healthy men, common side effects of Levitra were headache, flushing, nasal congestion and sometimes dizziness.

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