Critical Study of Blood Pressure Drugs Assailed : Medicine: Doctors urge patients to continue taking calcium-channel blockers. Tests that found increased risk of heart attacks were defective, they say.

A family of blood pressure drugs implicated in an increased risk of heart attacks has not been proved dangerous and patients should continue to take them without fear, Stanford and UC Irvine cardiologists said Friday.

Cardiologists locally and around the country have reported a flood of calls and visits from frightened patients since researchers from the University of Washington reported March 10 that the drugs, calcium-channel blockers, increase the risk of heart attack by 60%. As many as 6 million people in the United States currently take the drugs.

But Dr. David Abrahamson of UC Irvine said in a conference call to cardiologists throughout the state that the study had a defective design that called its results into question. “I don’t believe it is in any way scientifically valid,” he said. The call was sponsored by the drugs’ manufacturers.

Officials from the American Heart Assn. and the National Institutes of Health also recommended that patients continue to take the drugs, which are sold under such brand names as Cardizem, Adalat, Dilacor, Calan and Verelan. “Failure to take prescribed anti-hypertensive drugs may result in dangerously high blood pressure”--even higher than it was before the patient began taking the drug--an American Heart Assn. statement said.

Even the physician who made the March 10 report, Dr. Bruce Psaty of the University of Washington, urged patients to continue with their medication. “The immediate risk of a heart attack is low regardless of the type of therapy,” he said in a statement sent to doctors and patients. “You should stay on your medicines and discuss your concerns with your own private physician.”

Psaty and his colleagues studied 623 hypertensive members of a health maintenance organization in Washington who had suffered a heart attack between 1986 and 1993 and compared them to 2,032 matched people who were also hypertensive, but who had not suffered heart attacks.

They found that those who took a calcium-channel blocker alone or in combination with a diuretic (which rids the body of excess water) were 60% more likely to have a heart attack than those who took only a diuretic. But Psaty cautioned this week that the actual risk of heart attacks was quite low, regardless of whether the patients were taking the channel blockers. The risk was about 10 per 1,000 patients for those taking a diuretic, compared to 16 per 1,000 for those taking the questioned drugs.

Most critics, like Abrahamson, believe that those in the study who suffered heart attacks were more ill to begin with.

Critics argued, moreover, that the Psaty study was a “case control” study in which researchers worked backward, first identifying those who had a heart attack and then looking to see what risks they might have had in common. “This type of study, although useful, cannot provide definitive information on the effectiveness and long-term safety of a class of drugs,” according to the National Heart, Lung and Blood Institute.

Such conclusions can only be reached in a prospective study, in which patients are randomly assigned to receive one of the drugs being tested and then monitored.