Carvedilol improves components of the metabolic syndrome in patients with type 2 diabetes and hypertension, whereas metoprolol tartrate is associated with increases in hemoglobin [A.sub.1c] (Hb[A.sub.1c]) in this population.
The agents were compared in the multicenter trial, GEMINI (Glycemic Effects in Diabetes Mellitus: Carvedilol-Metoprolol Comparison in Hypertensives). The trial included 1,235 patients age 36 to 85 (mean age 61) with controlled type 2 diabetes (baseline HbA1c 6.5% to 8.5%) and Stage 1 or Stage 2 hypertension.
At study entry, patients on antidiabetic treatment must have been stable for at least 3 months, and received antihypertensive therapy for at least 1 month (therapy must have included an ACE inhibitor or angiotensin receptor blocker). Participants were randomized to carvedilol, titrated up to 25 mg/bid, or metoprolol, titrated up to 200 mg/bid.
Target blood pressure was 130-135/ 80-85 mm Hg, depending on baseline blood pressure. Hydrochlorothiazide and a dihydropyridine calcium antagonist could be added as necessary to achieve a target blood pressure of <130/80 mm Hg. Blind therapy was maintained 5 months following titration to target blood pressure.
Adverse effects in the metoprolol group and the subsequent discontinuance of the drug resulted in longer mean treatment duration in the carvedilol vs. the metoprolol group (155 vs. 147 days, p=0.01). Bradycardia occurred in 4.1% and 1.5% of metoprolol and carvedilol recipients, respectively.
"Carvedilol, in comparison to metoprolol, achieved blood pressure goal while maintaining glycemic control, improving insulin resistance, and reducing progression to microalbuminuria in these high-risk cardiovascular patients," said lead investigator George L. Bakris, MD, director of the Hypertension/Clinical Research Center Rush University Medical Center, Chicago.
Similar blood pressure levels were achieved in both groups. Withdrawals for worsening glycemic control occurred in 2.2% and 0.6% of metoprolol and carvedilol recipients (p=0.04), respectively. Mean HbA1c increased significantly (0.15%; p<0.001) with metoprolol, but not in patients who received carvedilol (+0.02%, p=0.65). An increase in HbA1c >1% was observed in 14.2% of metoprolol and 7% of carvedilol recipients (p<0.001). Insulin resistance by homeostatic model assessment improved significantly from baseline in patients on carvedilol (-9.1%; p=0.004) but not metoprolol (-2.0%; p=0.48), an effect that correlated with Hb[A.sub.1c].
Patients taking carvedilol had a 16.9% reduction (p=0.003) in albumin:creatinine ratio relative to patients taking metoprolol. Eighty percent of patients did not have microalbuminuria at study entry. Among these patients, risk of developing microalbuminuria was reduced by 47% with carvedilol relative to metoprolol (incidence: 6.6 vs. 11.1%; p=0.03).
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