Systemic and cardiac hemodynamic interactions between clonidine and minoxidil.

We examined the hemodynamic interaction between clonidine, a centrally acting antiadrenergic drug, and minoxidil, a potent antihypertensive vasodilator in 10 inpatients with refractory or accelerated hypertension or both. Clonidine in oral doses of 150 to 900 micrograms/day decreased average mean blood pressure 18.6 mm Hg (p less than 0.01), average heart rate 16.4 bpm (p less than 0.01), limb blood flow 1.63 ml/100 gm . min (p less than 0.05), and plasma renin activity 1.13 ng/ml . hr (p less than 0.025). It also increased the pre-ejection period index 12.4 msec (p less than 0.001), but did not alter the cardiac or total peripheral resistance indices. The addition of minoxidil in oral doses of 5 to 22.5 mg/day further decreased average mean blood pressure 24.2 mm Hg (p less than 0.01), preejection period index 20.6 msec (p less than 0.01), limb vascular resistance 13.2 mm Hg/min . 100 gm/ml (p less than 0.05), and total peripheral resistance 13.3 mm Hg/min . m2/l (p less than 0.01), pre-ejection period index 20.6 msec (p less than 0.01), limb vascular resistance 13.2 mm Hg/min . 100 gm/ml (p less than 0.05), and total peripheral resistance 13.3 mm Hg/min . m2/l concluded that clonidine can be used as an alternative to beta-adrenergic blockers to counteract the increased sympathetic nervous activity minoxidil induces.