Effect of carvedilol and metoprolol on blood pressure, blood flow, and vascular resistance.

Carvedilol and metoprolol were given for 4 weeks in a double-blind study to patients with essential hypertension. The effects on blood pressure were measured and hemodynamic alterations were assessed by forearm venous plethysmography before and after chronic administration, and 2 h after an acute dose before and during chronic therapy. Carvedilol (50 mg/day) reduced supine and erect blood pressure, and pulse rate similar to the reduction with metoprolol (100 mg b.i.d.). There was a tendency for forearm blood flow to rise and for forearm resistance to fall with both drugs. When administered acutely, there was no fall in pulse rate with carvedilol compared to the fall with metoprolol when on placebo or active therapy. The blood pressure fall with acute administration was similar with both drugs when not on treatment, but when on chronic therapy, there was no fall with metoprolol but a marked fall with carvedilol. In this circumstance, vascular resistance rose with metoprolol but not with carvedilol. No effect of either drug on a modified cold presser test was observed. Both drugs were well tolerated and there were no significant side effects except for an excessive fall in blood pressure in one patient on carvedilol. Plasma renin activity (PRA) fell with both drugs and there was a tendency for both plasma potassium and plasma uric acid to rise. Carvedilol was well tolerated and reduced blood pressure successfully.