After two years of spectacular mismanagement, will 2008 be the year that Encysive Pharmaceuticals (Nasdaq: ENCY) is finally able to capitalize on its very marketable lead drug, Thelin?

Thelin is Encysive's only in-house marketed drug. It treats a condition called pulmonary arterial hypertension (PAH) and is approved for marketing in the European Union and a few other places around the world, but not in the United States. Sales guidance provided by Encysive calls for 2007 sales to be a bit above the company's previous $10.5 million to $11.5 million forecast, with 2008 estimates for worldwide sales in the $40 million to $50 million range.

Last week, both of Encysive's most direct competitors, Actelion and Gilead Sciences (Nasdaq: GILD) reported fourth-quarter sales numbers for their similar compounds. In the fourth quarter, sales of Actelion's Tracleer were up an incredibly strong 34% year over year, topping $300 million and showing no signs of a sales slowdown despite having been on the market for more than six years in some places.

Sales of other PAH treatments have been strong as well in the fourth quarter. Gilead's Letairis, which is only approved in the U.S., brought in a respectable $15 million in the fourth quarter, in only its second full quarter on the market. Sometimes competitor and sometimes complementary treatment Revatio (known more commonly as Viagra) from Pfizer (NYSE: PFE) also experienced another solid quarter of 10% sales growth, although Pfizer doesn't break out the portion of Viagra sales meant for treating pulmonary arterial hypertension.

Almost every approved PAH treatment has shown strong sales growth in recent quarters, and there are a host of drugmakers, like United Therapeutics (Nasdaq: UTHR) and BioMarin (Nasdaq: BMRN), with innovative new treatments in development. 

Pulmonary arterial hypertension is a market that is undoubtedly (and unfortunately) experiencing a large market expansion as more and more patients are correctly diagnosed and put on PAH drugs. The market opportunity in the U.S. and Europe is huge.

It will probably be another two years before Encysive's Thelin will be on the market in the United States, because the FDA wants more efficacy data before approving it. Encysive is planning to begin a phase 3 study in the second quarter. The main question now is what highly diluted shape Encysive will be in by the time Thelin gets to the U.S. market.

BioMarin is an active pick of our Rule Breakers newsletter. Pfizer is a pick of the Inside Value newsletter.

Fool contributor Brian Lawler does not own shares of any company mentioned in this article. The Fool has an A+ disclosure policy.