Drug manufacturer Pfizer Inc. said Wednesday that it would buy biopharmaceutical company Encysive Pharmaceuticals Inc. for about $195 million and its Thelin lung-disorder drug that had repeatedly failed to win approval in the United States.

The new acquisition is meant to strengthen Pfizer’s portfolio in products treating high blood pressure.

The New York pharmaceutical company will acquire this way the rights to Encysive’s Thelin (R) (sitaxsentan sodium), an oral, once-daily endothelin, a drug that treats pulmonary arterial hypertension, which refers to high blood pressure in the pulmonary artery.

Thelin has already been approved for marketing in the European Union (EU) and is currently available in many EU states, including the United Kingdom, Germany, Ireland, Spain, France, Italy, Belgium, Luxembourg, and the Netherlands. The drug has also been approved in Australia and Canada. In the United States, Thelin has received three approval letters from the Food and Drug Administration, but failed to win final approval.

“Pfizer plans to conduct a pivotal Phase III trial to support registration in the U.S.” of Thelin, Pfizer said in a statement, according to Reuters.

The deal between the two companies is expected to close in the second quarter.

Pfizer posted 2007 revenue of about $48.61 billion.

On Tuesday, Pfizer shares closed up 4 cents, or 0.2%, to $22.37 while Encysive shares closed up 23 cents, or 27%, to $1.08.

Encysive has about 79.3 million shares outstanding.