Pharmacological studies on cadralazine: a new antihypertensive vasodilator drug

Cadralazine is a new, orally effective antihypertensive vasodilator. Acute experiments indicate that the compound reduces blood pressure and increases heart rate. The doses which reduce systolic blood pressure by 25% (ED25) are very similar after oral and intravenous administration (spontaneously hypertensive rats, 1.8 mg/kg, p.o.; 2.3 mg/kg, i.v.; renal hypertensive dogs, 0.26 mg/kg, p.o.; 0.24 mg/kg, i.v.; awake normotensive dogs, 0.98 mg/kg, p.o.; 1.01 mg/kg, i.v.). By both routes the peak effect is reached after 3-5 hr, and the activity lasts more than 24 hr. Repeated oral administration in spontaneously hypertensive rats reduces blood pressure with no evidence of tolerance. Cadralazine reverses hypertensive responses to epinephrine in awake normotensive dogs and anesthetized cats. The inhibition of the increase in blood pressure induced by sympathetic outflow activation in pithed rats parallels the antihypertensive activity in onset, intensity, and duration. The effects of cadralazine are not due to a blockade of alpha-adrenoceptors, sympathetic neurons, or ganglionic transmission. Cadralazine has no antihistaminic, anticholinergic, or spasmolytic activity and no specific effect on behavioral tests. In comparison with hydralazine, cadralazine has less acute toxicity and a greater activity by the oral route.