This week could be quite exciting, drug investors. We've got a trio of PDUFA dates coming up, followed with one more next week.

Of course, the Prescription Drug User Fee Act doesn't require the Food and Drug Administration to act on the date -- it's just sort of a hazy, general goal by which the agency should try to make up its mind. So we could have three decisions, or we might have none. At least it'll keep the day traders on their toes.

For more Foolish, longer-term investors, let's take a look at the potential winners -- and invest if the price seems right.

A stronger ... heart?
Eli Lilly's (NYSE:LLY) erectile dysfunction drug Cialis is getting repurposed. Instead of helping men make their partners smile, Lilly hopes the drug will get approved to help the hearts of patients with pulmonary arterial hypertension (PAH), a form of high blood pressure. Last year, the drugmaker sold the rights to market Cialis for PAH to heart expert United Therapeutics (NASDAQ:UTHR), which already markets PAH drug Remodulin, and has a few more PAH drugs in development.

Marketing erectile dysfunction drugs for PAH isn't a novel idea, Pfizer's (NYSE:PFE) Viagra is marketed under the name Revatio to treat PAH. That's good news for Eli Lilly and United Therapeutics, because the companies announced this morning that the FDA has indeed approved the drug, to be marketed as Adcirca. Now its greatest remaining hurdle is its well-established competition.

Side effects strike back
All signs point to an eventual thumbs-up for Bayer and Johnson & Johnson's (NYSE:JNJ) Xarelto; the FDA advisory panel voted 15 to 2 in favor of approval. But that good news might not arrive before the PDUFA date of May 28. Xarelto is an effective blood thinner, but the FDA and its advisory panel are worried about its potential to cause liver damage and excessive bleeding.

As the agency has done so many times recently, it may come back with a complete response letter asking the companies to develop a Risk Evaluation and Mitigation Strategy (REMS), which would encourage doctors not to prescribe the drug off-label.

A delay and/or a restrictive label would be perfectly OK with sanofi-aventis (NYSE:SNY), which sells the blockbuster blood thinner Lovenox. Xarelto clearly has a marketing advantage; it's an oral medication, while Lovenox needs to be injected.

Expanding possibilities
ViroPharma (NASDAQ:VPHM) got Cinryze approved last fall as a prophylactic treatment for hereditary angioedema (HAE), a rare and potentially fatal disease marked by swelling that can cut off the airway. ViroPharma is back for more, hoping to get Cinryze approved to treat the acute attacks.

Given the life-threatening nature of HAE, the FDA gave Cinryze a six-month priority review, putting its PDUFA date on June 3. If ViroPharma does get the green light to market Cinryze as an acute treatment, it'll have a head start on Dyax, which received a complete response letter for its acute HAE drug, DX-88, in March. The delay was good news for ViroPharma, but Dyax should be able to get the drug on the market eventually.

Cinryze might also go head-to-head with CSL Behring's Berinert-P, which is already approved in other countries, and is up for review at the FDA for treating acute episodes of HAE.

Finally, GlaxoSmithKline (NYSE:GSK) and Denmark's Genmab are expecting word on Friday regarding an FDA panel decision on Arezza, a new leukemia drug. Early talk suggests that this one will go through, but investors and analysts have been wrong before. Glaxo hopes this drug will mark the company as a major player in the cancer-treatment market.

Tell us what you think
Not interested in the extreme binary events that often have drastic effects on drugmakers' stock prices? You can still play along at home, by telling us what you think in the Motley Fool CAPS. Let us know whether you think the drug decisions will help these companies outperform the S&P500, or whether they're just duds. It's free to play, and best of all, you might get a few investment ideas from fellow Fools.

Pfizer is a Motley Fool Inside Value pick. Johnson & Johnson is an Income Investor selection. Whether you like your companies big or small, dividend-laden or packed with multibagger potential, we have a newsletter service for you.

Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool's disclosure policy really isn't sure what sitting outdoors in a bathtub has to do with erectile dysfunction.