Labetalol: Bioavailability, Drug Plasma Levels, Plasma Renin and Catecholamines in Acute and Chronic Treatment of Resistant Hypertension

Summary: Labetalol: Bioavailability, drug plasma levels, plasma renin and catecholamines in acute and chronic treatment of resistant hypertension. W. J. Louis, N. Christophidis, M. Brignell, V. Vijayasekaran, J. McNeil and F. J. E. Vajda, Aust. N.Z. J. Med., 1978, 8, pp. 602–609. The antihypertensive effects of labetalol have been studied in 30 patients with severe hypertension. In seven of these patients acute administration was associated with falls in blood pressure which were maximal at two minutes, for intravenous injection and one hour for oral administration. The bioavailability of acute oral administration was studied and varied between 11 and 76%. There were no statistically significant changes in plasma renin and plasma catecholamines following acute administration. In 30 patients labetalol was administered, usually together with a thiazide diuretic, on a chronic basis over a period of ten months. There was a significant relationship (r = 0–517, P & lt; 0001) between drug dosage and plasma levels and in four cases poor response could be attributed to low peak plasma levels of the drug. Improved blood pressure control was associated with a substantial reduction in the number and type of tablets patients were taking and an overall reduction in side effects. The commonest side effect was mild postural hypotension. In addition, one patient in the trial and another more recently have shown hyper-reactivity to the drug and developed profound postural hypotension with the initial dose. We conclude that labetalol when combined with a thiazide diuretic is an important therapeutic advance in the treatment of the difficult hypertensive subject.