Encysive Pharmaceuticals (Nasdaq: ENCY) appears to have engineered a sale of itself just in time. Yesterday, the European Union's medical authorities said they had issued a positive opinion that will allow a rival pulmonary arterial hypertension drug onto the market in a few months.

Encysive's lead compound is pulmonary hypertension treatment Thelin, a drug that's often compared to Gilead Sciences' (Nasdaq: GILD) and GlaxoSmithKline's (NYSE: GSK) ambrisentan because both compounds have similar effects on the body. Ambrisentan was the drug that got the nod yesterday. As a result of that ruling, Glaxo is allowed to start selling ambrisentan in the E.U. in 60 to 90 days.

But Glaxo won't have the advantage of competing against a diminutive rival in the E.U. anymore. Encysive leveled the David-and-Goliath battle against Glaxo in the multibillion-dollar pulmonary hypertension market two days ago, when it agreed to be acquired by Pfizer (NYSE: PFE) for $195 million in cash.

Thelin sales won't start feeling the effects of competition from ambrisentan for a while. Glaxo still has to negotiate reimbursement pricing among many of the European countries where it will sell the drug, which will go by the brand name Volibris. Last year, Encysive recorded $12 million in worldwide sales and has guided for $40 million to $50 million in sales for 2008.

The pulmonary hypertension drug market is in its infancy and still carries an orphan indication, although it's growing quickly. In fact, Thelin and Volibris are far from the only drugs to treat pulmonary hypertension, a condition that can make walking even a few feet difficult and tiring. Last year, Gilead's U.S. sales of ambrisentan were in the low-double-digit millions.

The E.U. approval of ambrisentan came a little sooner than Encysive and Pfizer probably would have liked, but it was expected, considering the drug's efficacy, safety, and 2007 FDA approval.

Instead, the early approval of ambrisentan is more troublesome for Actelion's Tracleer, the leader in the endothelin receptor antagonist category of pulmonary hypertension treatments. Last year, sales of Tracleer topped $1 billion worldwide, so ambrisentan will bite into Tracleer's sales fortunes much more than it will Thelin's.

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