The National Heart, Lung, and Blood Institute (NHLBI) halted at least one part of a large study of the blood pressure drug doxazosin because patients on the drug did not do as well as those on an alternate medication. Patients taking the drug, also known as Cardura, should see their doctor and not halt the medication on their own, the federal agency warned.

The decision, which NHLBI made following an independent data review by an advisory committee, was announced on March 10. The study is called ALLHAT (Antihypertensive and Lipid Lowering Treatment to Prevent Heart Attack Trial) and includes more than 42,000 people over age 55 in the US, Canada, Puerto Rico, and the US Virgin Islands.

The study participants have high blood pressure and at least one heart disease risk factor, such as diabetes, high cholesterol or smoking. The patients are taking a variety of blood pressure-lowering drugs, including doxazosin (an alpha-blocker), a diuretic known as chlorthalidone, a calcium antagonist called amlodipine, and an ACE inhibitor called lisinopril.

There was a 25% higher rate of combined cardiovascular events in the doxazosin group and especially a two-fold increase in heart failure rates (compared with those taking chlorthalidone).There was also a tendency towards more strokes in the doxazosin group.