Use of the alpha-blocker doxazosin has been stopped in a large US hypertension study because the drug was found to be less effective than a traditional diuretic in reducing some forms of cardiovascular disease.
The ALLHAT (antihypertensive and lipid lowering treatment to prevent heart attack) trial, run by the National Heart, Lung and Blood Institute, is one of the trials currently under way to compare newer antihypertensive drugs with the well established beta-blockers and diuretics.
A statement issued by the NHLBI says that the doxazosin arm of the study was stopped on the advice of the trial's advisory committee. The drugs were similarly effective in preventing heart attacks and in reducing the risk of death from all causes but users of the alpha-blocker had 25 per cent more cardiovascular events and were twice as likely to be hospitalised for congestive heart failure as users of chlorthalidone.
The rest of the ALLHAT study, which began in 1994, is continuing as planned and is expected to end in 2002. All patients in the trial have hypertension plus one other risk factor for coronary heart disease. The trial is comparing chlorthalidone with the calcium channel blocker amlodipine and the ACE inhibitor lisinopril.
Pfizer (manufacturer of doxazosin) said that the findings were unexpected given the large amount of trial data showing doxazosin to be an effective and well tolerated treatment for hypertension. "However, we can conclude, as the NHLBI have done, that the doxazosin arm of the study was not discontinued on safety grounds, rather that it was not as effective as chlorthalidone in reducing CHF."
The company added that chlorthalidone was an approved treatment for CHF in addition to hypertension. "Doxazosin is not indicated to treat CHF and, as such, a reduced rate of CHF might be anticipated in the diuretic group."