Impotence Drug Takes on Viagra
By Kristen Philipkoski
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http://www.wired.com/news/medtech/0,1286,59273,00.html02:00 AM Jun. 17, 2003 PT
Carl Spana could almost be talking about a miracle plant food -- or perhaps floor wax -- when he discusses his company's erectile dysfunction drug.
"It produces a very high-quality erection," said Spana, president and CEO of Palatin Technologies, in a recent interview.
Despite his matter-of-fact tone, Spana is aware that his drug is designed to treat the vagaries of sexual dysfunction, and therefore must be tested in a real-life setting, not just in the lab. The company is recruiting patients for a study that will examine PT-141's effectiveness in real-life sexual encounters. Patients will report on their experiences by answering questionnaires similar to those used to evaluate Viagra, the only erection drug approved in the United States.
"This is the first time we're looking at patients in their homes when they're engaging (in) sexual interactions," Spana said.
He hopes the drug, now called PT-141, will give Viagra a run for its money. It differs from Viagra in many ways -- for one, it's administered as a nasal spray rather than in pill form.
PT-141 has cleared the first phase of clinical trials necessary for Food and Drug Administration approval. In those studies, researchers found that the drug helped male patients achieve their ultimate goal: blood flow to the penis resulting in a sustained erection. In fact, when measured using a device called a RigiScan, the erections lasted up to three hours.
Palatin researchers found that many patients who didn't achieve an erection taking Viagra did succeed with PT-141.
They also found the drug seemed to help patients overcome performance anxiety because, unlike Viagra, it works with or without visual or tactile stimulation.
The potential market for new drugs that treat sexual dysfunction appears promising. Up to 30 million men suffer from erectile dysfunction in the United States, but only 8 million take Viagra, according to a review of erectile dysfunction therapies published in the September 2002 issue of Nature Reviews Drug Discovery.
So even with two Viagra-like drugs coming down the pike by the end of this year -- Levitra from Bayer and Cialis from Eli Lilly -- Spana believes there's room in the marketplace for more treatments.
"This is sex, and at the end of the day, people have different sexual preferences," Spana said. "It's a quality-of-life issue, and people like choice."
Ching-Shwun Lin, an associate professor of urology at the University of California at San Francisco, agrees with Spana about the potential for more treatments, but he is taking a different approach to the problem.
Lin is studying the genes involved in erectile dysfunction in hopes of finding a way to manipulate them in order to prevent the condition. He has filed for patent protection on his work.
"We are working on the cure rather than a temporary treatment," he said.
Meanwhile, other researchers studying treatments for sexual dysfunction see opportunities in products designed for a different audience: women.
Such treatments have been slow to hit the market, in part because sexual responsiveness in women is more difficult to measure, researchers say.
Whereas the sexual arousal of men is clearly shown by an erection, women's sexual arousal requires increased blood flow to the vagina as well as lubrication and a desire for sex.
While it seems likely that drugs like PT-141 can increase the amount of blood sent to the vaginal area, it's not necessarily true that such a treatment would increase a woman's sexual satisfaction.
"Things are always somewhat murky in women," Spana said. "The drug has to work for both desire and arousal problems, whereas men normally have a libido."
Palatin researchers will test PT-141 in women later this year, he said.
The drug, which is administered nasally because researchers found it worked best that way, is safe for people who take nitrates for heart conditions.
That fact sets it apart from Viagra, which can cause life-threatening hypotension (extremely low blood pressure) when taken with nitrates. And since Cialis and Levitra work by the same mechanism as Viagra, they will likely be dangerous in combination with nitrates as well, researchers say.
Viagra, Cialis and Levitra all work in essentially the same way, by blocking a molecule called a PDE5 inhibitor. PDE5 is essentially the molecule that prevents a man from getting an erection every time he sees a Victoria's Secret catalog. The drugs block that inhibitor, making an erection possible when combined with arousing images or touching a sexual partner.
PT-141 has a different biological effect. Instead of blocking the PDE5 inhibitor, it causes a cascade of events that leads to an erection: It stimulates nerves that release molecules that cause the penis to become engorged with blood. They're the same nerves that are activated by natural sexual arousal.
"We're doing pharmacologically with a drug what the nerves normally do," Spana said.
Side effects observed in about 10 percent of patients were face flush and mild nausea, which thankfully occurred about four hours after taking the drug.
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