Treatment of severe hypertension by repeated bolus injections of labetalol.

Repeated intravenous bolus injections of labetalol were administered to 15 severely hypertensive patients. In 11 instances, a standard protocol was followed in which a loading dose of 1 mg/kg was given intravenously over 1 min, followed by up to five bolus injections of 50 mg at 10-min intervals. In two further patients, bolus doses varying from 25-100 mg were given after the loading dose, and in two others the loading dose was omitted. Falls in systolic BP ranging from 26-194 mmHg were seen in 14 patients and of diastolic BP from 16-76 mmHg in 13. In one patient there was no appreciable fall in either systolic or diastolic BP and in one no marked fall in diastolic BP, although systolic BP dropped by 42 mmHg. The reduction in arterial BP was smooth in ten patients. In four patients a steep fall in BP, of 194 to 101 mmHg systolic, was seen within 10 min of an injection of labetalol; in all four hypotension was readily controlled by elevating the foot of the bed. Side-effects included nausea, vomiting, epigastric discomfort, scalp tingling, burning sensations in the throat and groin, shivering, and pain at the site of injection. Side-effects limited the dose given in four patients. In no case was there clinical or electrocardiographic evidence of myocardial ischaemia induced by labetalol. Labetalol, given by bolus injection, appeared less efficient in controlling arterial pressure, and more likely to cause side-effects, than when given, as in a previous study, by incremental infusion. When labetalol is to be given intravenously for the control of severe hypertension, incremental infusion, rather than bolus injection, is preferred.