Acute haemodynamic effects of labetalol and its subsequent use of an oral hypotensive agent.

1 Fourteen patients whose lying diastolic blood pressure was persistently 110 mmHg or greater were given labetalol 0.5--1 mg/kg intravenously. 2 The maximum hypotensive effect developed between 20 and 40 min, and on average lasted 3 h. The lying systolic mean blood pressure fell by 30 mmHg and the lying diastolic blood pressure by 17 mmHg (P less than 0.001). 3 This acute hypotensive effect was associated with a significant reduction in the peripheral resistance (P less than 0.02). The hypotension was not associated with significant secondary changes in the stroke volume or pulse rate. 4 The above 14 patients plus 1 additional subject received labetalol orally at a daily dose ranging from 150-2400 mg. The mean lying systolic blood pressure fell by 22 mmHg (P less than0.01) and the mean lying diastolic blood pressure by 26 mmHg (P less than 0.001). The standing values were similar and postural hypotension at this dose did not develop. There was no significant change in the pulse rate. 5 Renal function was monitored by estimates of plasma creatinine and creatinine clearance. Some patients were followed for 2 yr and others for a few months. With the long-term patients, there was no significant reduction in either measurement although in a few patients a slight reduction in creatinine clearance was observed.