TUESDAY, Dec. 14, 2004 (HealthDayNews) -- A study of recommended blood pressure drugs has produced a result even the researchers find hard to explain: Adding a calcium channel blocker to a diuretic was associated with an increase in deaths but not an increase in incidence of stroke or coronary events such as heart attacks.
It's a finding that highlights the caution with which physicians approach observational studies, which look backward at the experience of patients. The preferred method is a controlled trial, in which all the elements of treatment are carefully monitored from the start.
The new study was based on an observational trial, the Women's Health Initiative Observational Study, which included more that 93,000 women aged 50 to 79 who were followed for an average of 5.9 years.
The findings appear in the Dec. 15 issue of the Journal of the American Medical Association.
The idea was to look at the results of current U.S. recommendations that treatment of high blood pressure should start with a diuretic, a widely available and inexpensive class of medications that promote the excretion of urine to rid the body of excess fluid. If a diuretic doesn't result in proper blood-pressure control, another drug should be added -- either a calcium channel blocker, a beta blocker, or an ACE inhibitor, the guidelines state.
The new study found that women who had high blood pressure but no cardiovascular disease who were given a diuretic and a calcium channel blocker had an 85 percent higher death rate than those given a diuretic plus a beta blocker. But the incidence of coronary events and strokes was the same in both groups. The study did not specify the causes of death.
Study author Sylvia Wassertheil-Smoller acknowledged that observational studies have their drawbacks. But, she said, "There have been no controlled trials of this particular combination [a diuretic and a calcium channel blocker]."
By contrast, the ALLHAT controlled trial, which is regarded as the definitive U.S. study of treatment for high blood pressure, found no difference in mortality rates, said Wassertheil-Smoller, head of the division of epidemiology at the Albert Einstein College of Medicine in New York City.
However, the ALLHAT study only examined the use of a single drug to treat high blood pressure. Before any action is taken based on the new finding, said Wassertheil-Smoller, "we would need a clinical trial in which people were put on a diuretic and then randomized to an additional drug."
Dr. Daniel W. Jones, dean of the University of Mississippi Medical Center and a spokesman for the American Heart Association, couldn't agree more.
"This study, despite the fact that it is a strict study done by good people, does not have a conclusive character," Jones said. "This is observational data -- high-quality observational data obtained by high-quality people -- but you simply can't draw firm conclusions from it."
The finding "is not consistent with most randomized trials, which show that lowering blood pressure with any therapy reduces cardiovascular events," Jones said.
In his practice, Jones said, he will continue to follow the recommendation stemming from the ALLHAT trial -- starting treatment with a diuretic and adding another drug if the goal of reducing blood pressure to no more than 140 over 90 is not achieved. The choice of a second drug, (or third, if necessary), is not important to him, Jones said: "I use all of those classes."
"The evidence strongly suggests that the mechanism by which we get there is not nearly as important as lowering blood pressure itself," he said.
A guide to drug treatment of high blood pressure is offered by the American Heart Association.