Rate of onset of hypotensive effect of oral labetalol.

1 Labetalol caused a fall in blood pressure within 2 h or oral doses of 100, 200 and 400 mg in six hypertensive patients. 2 This fall which was dose-related was maximal by 3 h and was sustained when the drug was given in doses of 100 mg 8 hourly, 200 mg 8 hourly and 400 mg 8 hourly. 3 This rapid fall in pressure when labetalol is given by mouth which contrasts to that seen on administration of pure beta-adrenoceptor blocking agents is a valuable therapeutic property.