American Heart Association - New Orleans

Reassessing Calcium Channel Blockers


New Orleans - “The reason they became very popular is that they work, and they work very well.” That was the message about calcium channel blockers from Dr. Henry R. Black, of Rush Presbyterian - St. Luke’s Medical Center in Baltimore. Dr. Black was speaking at a plenary session devoted to calcium channel blockers (CCBs) at the 69th Scientific Sessions of the American Heart Association, which took place the week of November 10th, 1996, in New Orleans.

Not all CCBs are created equal

Addressing the current controversy about the use of CCBs, Dr. Black sounded a cautionary note against extrapolating from one trial’s findings to general use. Although the CCBs comprise one type of drug, their actions and effects are not homogeneous; as Dr. Black noted, even CCBs of the same kind (e.g., all dihydropyridines) can have different effects.

Despite these differences, CCBs do share something in common: potential benefits. All drugs of this type lower heart rate, blood pressure, and myocardial contractility; they increase coronary flow; and they suppress ventricular arrhythmias.

Not all trials are created equal

Dr. Black summarized characteristics and evidence from several trials of CCBs, remarking that the drugs seemed to be most effective for patients who had been randomized to them first. He also pointed out that, in the TOMHS trial, all classes of drugs tested appeared to be equally good, but patients were more likely to stay on CCBs, those drugs being more tolerable and effective at low doses.

There are many ways of obtaining evidence of a drug’s effects: observation, retrospective and prospective studies, meta-analyses, etc. Dr. Black said that much of the information about CCBs is unreliable, especially that arising from meta-analyses or small trials. Sometimes factors are not adequately adjusted for -- for instance, subjects are in worse health than the controls.

The future of CCBs

Dr. Black also questioned the proliferation of new CCBs. “Are the new drugs worth it?” he asked. He remarked that the newer CCBs seem no more or less efficacious than the older ones, and that their safety in long-term use has not been established.

“It’s important to distinguish between no effect and inability to find effect,” he said in reference to inconclusive studies and uncertainty about CCBs’ merits. He summarized the state of evidence for and against CCBs by quoting Michael Crichton: “Absence of proof is not proof of absence.”