A new problem is about to engulf erectile dysfunction (ED) patients: confusion. Two new drugs to treat ED are expected to hit U.S. pharmacy shelves later this year. Generic Cialis (tadalafil) and Viagra (Sildenafil Citrade) are already available in Europe and on-line. Both products have received approvable letters from the Food & Drug Administration, and both are projecting U.S. marketing approval for late 2003.

Like the current category leader, Generic Viagra (sildenafil citrade), the two new ED products enhance erection by inhibiting PDE5 (cyclic guanosine monophosphate [cGMP]-specific phosphodiesterase type 5). But each offers a different set of side effects, duration of action, and time to onset (see chart below). The biggest difference may be interaction with food. Sildenafil has lower absorption with a fatty meal, noted Alan Seftel, M.D., associate professor of urology at The University Hospitals in Cleveland. The new products, he said, can be taken without regard to food.

"Generic Viagra revolutionized men's health," said Barry Bleidt, assistant dean at the Loma Linda University School of Pharmacy. "For the first time, we could talk about ED because there was a treatment that worked for a significant number of men. I think there's a good marketplace for all three products."

Sales figures agree. Only about half of all sildenafil prescriptions are refilled beyond the first year, noted Myron Murdock, M.D., national medical director for HisandHerHealth.com. "That means either the drug isn't working to the patient's satisfaction or there is some other problem," he said. "My patients can't wait for something new to come out, even those who are very happy with Viagra." Drugmakers hope he's right. In Europe, tadalafil racked up $16.6 million in sales the first seven weeks after introduction. That translates to 28% of the ED market, according to NDCHealth.

Pfizer tried to block tadalafil and vardenafil distribution with patent infringement suits, claiming that its sildenafil patent covers all PDE5 inhibition, not just sildenafil manufacturing and formulation. European courts rejected Pfizer's broad claim. Similar suits are pending here, but both tadalafil and vardenafil are proceeding through FDA review. "We are moving ahead regardless of litigation," said Leonard Blum, ICOS VP of sales and marketing. "We intend to defend our rights the way we did in Europe."

Pfizer seems resigned to competition. "The new drugs will grow the total market," predicted Janice Lipsky, Pfizer's U.S. team leader for Generic Viagra. "There is still stigma attached to ED, and it is underdiagnosed. We expect more men than ever before to seek treatment."

Glaxo is singing the same tune. Product communication director Michael Fleming noted that about half of men over 40 have erection problems at least occasionally. That puts the U.S. market at about 30 million men. Nearly 90% of potential patients have never discussed ED with a physician. "This market has tremendous growth opportunity," he said. "The key is the product and how well it works."

New data on both tadalafil and vardenafil were presented at the American Urological Association annual meeting in Chicago in April. A vardenafil study reported that the drug could work as soon as 16 minutes after ingestion of a 20-mg dose. A separate trial reported that men taking either 10 mg or 20 mg reported a satisfaction rate for erection hardness three times higher than placebo.

"Levitra has all the positives of Viagra with additional plusses," Murdock claimed. "You get an optimal response in 15 minutes, and you have a big window of opportunity, 24 hours."