Exactly why the beta blocker drug nebivolol works better than some other medicines in American blacks is not clear. But doctors do acknowledge that medications vary in their effectiveness sometimes from race to race.

"This particular beta blocker seems to work better in African-Americans than other beta blockers on the market," said Dr. Elijah Saunders, professor of medicine in the division of cardiology and hypertension at the University of Maryland School of Medicine, Baltimore.

His findings were to be presented Sunday at the International Society on Hypertension in Blacks conference, held in San Juan, Puerto Rico.

In the past, Saunders said, beta blockers -- a class of drugs used to treat high blood pressure -- have not been shown to be as effective in black patients as in white patients. Beta blockers work by reducing nerve impulses to the heart and blood vessels, making the heart beat slower so blood pressure drops.

In this new study, Saunders and his colleagues randomly assigned 300 black patients with mild-to-moderate high blood pressure to receive either a placebo or nebivolol in one of a number of doses (2.5, 5, 10, 20 or 40 milligrams) daily for 12 weeks. For safety purposes, those taking a placebo had blood pressures that were only mildly elevated, Saunders added.

To be enrolled in the study, participants had to have diastolic blood pressures from 95 to 109 millimeters Hg.

Diastolic blood pressure, the bottom reading, refers to the measure taken when the heart relaxes between beats. Systolic blood pressure, the top reading, refers to the measure of the force of blood in the arteries when the heart beats. Experts now define normal blood pressure as ideally below 120/80; medication is often begun when pressures rise consistently above 140/90.

According to the researchers, reductions in diastolic blood pressure ranged from nearly 9mm Hg in the nebivolol groups to just a 2.8 mm Hg reduction with placebo. Systolic reductions ranged from 7.6 mm Hg in the nebivolol group and 0.4 with placebo.

Mylan Laboratories, which plans to market nebivolol in the United States, supported the study.

Nitric Oxide-Enhancing Beta Blocker

"This drug has not been used in this country at all," except for clinical trials, Saunders said. "It is not yet approved."

There is a perception that beta blockers are not effective in blacks, Saunders said. But this study refutes that idea, he said.

Recently, another drug, BiDil, was approved as a heart failure medication for black patients, triggering debates about the ethics of marketing medicine to particular races. But doctors do acknowledge that medications vary in their effectiveness sometimes from race to race.

Exactly why nebivolol works better than some other medicines in American blacks is not clear, but Saunders said there are several theories.

"There may be a reduction in the production of nitric oxide in African-Americans compared to whites," he said. "Nebivolol is a nitric oxide-enhancing beta blocker -- we think it could work better because of this specific effect that other beta blockers do not have." Nitric oxide is a known blood pressure regulator.

Another expert, Dr. Paul Underwood, a Phoenix cardiologist and president of the Association of Black Cardiologists, praised the study. "We're excited to add another therapeutic tool to the armamentarium in the treatment of high blood pressure in African-Americans," he said.

Depending on future studies of the drug and its effectiveness, Underwood said he would consider prescribing nebivolol, if and when it comes on the market.

He agreed that the nitric oxide mechanism may be important.

In another presentation at the San Juan meeting, researchers from Case Western Reserve University in Cleveland found that diuretics, the so-called water pills used to treat high blood pressure, are the preferred initial medicine for high blood pressure in blacks, even if the patients have risk factors such as obesity.

More information: To learn more about high blood pressure, visit the National Heart, Lung, and Blood Institute.