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The beta-blocker carvedilol (Coreg, GlaxoSmithKline) lowers blood pressure without negatively affecting glycated hemoglobin (A1C), according to research presented at the November 2004 American Heart Association Scientific Sessions in New Orleans.
Physicians treating diabetic patients may want to consider the use of carvedilol to manage certain cardiovascular risk factors and components of the metabolic syndrome, says lead author George L. Bakris, MD, director of the hypertension research center at Rush University Medical Center in Chicago. Some components of the metabolic syndrome are worsened by certain beta-blockers, the study notes.
"Side effects are the Achilles' heel of beta-blockers," Bakris says. "This gets you to where you need to be as far as blood pressure goes without the extra baggage of worrying about the other cardiovascular risk factors getting worse."
Yet some critics say there are limitations to the study and question whether the apparent advantages of carvedilol are worth its high price tag.
The 1,235-patient study compared the effects of carvedilol with those of metoprolol tartrate (Lopressor, Novartis) in patients with type 2 diabetes and hypertension. The findings also appear in the November 10 issue of JAMA.1
Results of the 6-month randomized, double-blind trial, known as GEMINI (Glycemic Effects in Diabetes Mellitus: Carvedilol-Metoprolol Comparison in Hypertensives), show patients in the carvedilol arm reached blood-pressure goals of less than 130/80 mmHg at a mean daily dose of 18 mg twice a day, close to the commonly prescribed dose. Patients receiving metoprolol tartrate required a mean daily dose of 128 mg twice a day to achieve similar blood-pressure goals.
As for diabetes control, patients taking carvedilol showed no statistically significant increase in A1C, an indicator of glycemic control, over the preceding 2–3 months (a 0.02% change from baseline). Meanwhile, those taking metoprolol had an average 0.15% increase in A1C. Twice as many patients receiving metoprolol had A1C changes of 1% or more.
Insulin resistance decreased 9.1% in the carvedilol-treated patients. The 2% reduction in insulin resistance for the metoprolol-treated patients was deemed not statistically significant.
The subjects also received conventional diabetes therapy as well as either ACE-inhibitors or angiotensin II receptor blockers.
"Always start out with an ACE-inhibitor and add beta-blockers if needed," says study co-author David S. H. Bell, MD, of the University of Alabama at Birmingham. "Beta-blockers have clearly been shown to improve mortality and morbidity, even in [diabetic patients]."
Although carvedilol did not increase blood-glucose levels, Bakris notes that the effects of the drugs on clinical outcomes, such as cardiovascular events and mortality, have not been compared in long-term clinical trials.
The short length of the GEMINI study is one of its limitations, says cardiologist Prakash C. Deedwania, MD, chief of cardiology at the VA Medical Center in Fresno, Calif., and a professor at the University of California at San Francisco's Fresno Medical Education Program.
"It is only a 6-month study that does not really speak to what the long-term effects will be, whether these effects will be sustained," Deedwania says.
"Number two, I'm not necessarily sure that there are advantages that outweigh the cost consideration," he continues. "Indeed, the cost of carvedilol is at least three to four times higher [than metoprolol]. The question can be raised whether the short-term benefit of A1C really does provide a cost-benefit ratio that is clinically meaningful and cost-saving."
Carvedilol may be different from metoprolol in some ways, but there is
nothing uniquely superior in carvedilol, Deedwania says. He adds that all
beta-blockers are safe, effective, and cardio-protective in the setting of
hypertension and coronary-artery disease. 
Footnotes
Note: GlaxoSmithKline was involved in the design and analysis of the GEMINI trial.
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