Monotherapy with labetalol for hypertensive patients with normal and impaired renal function

Labetalol in the treatment of hypertension in patients with normal and impaired renal function

Labetalol (Trandate) is a new antihypertensive agent with both alpha- and beta-adrenoceptor blocking properties. In a double-blind cross-over study the antihypertensive action and side-effects of labetalol and propranolol were compared in 18 previously untreated outpatients with hypertension, WHO stage I--III. Mean daily dose of labetalol was 667 mg and of propranolol 129 mg. Labetalol reduced systolic and diastolic blood pressure in the seated and upright position significantly more than propranolol. The pulse rate reduction was greater with propranolol. Side-effects were more pronounced with propranolol. The antihypertensive effect, effect on pulse rate and pharmacokinetics of a single oral dose of 400 mg labetalol were studied in 6 patients with normal and 6 patients with impaired renal function (creatinine clearance less than 20 ml/min), all belonging to WHO stage I--II. A significant fall in pulse rate and systolic and diastolic blood pressure was observed in both groups, the duration being more than 25 h. No difference was found between the two groups. From the serum concentration-time curves the elimination rate constant, elimination half-life and area under the curve were calculated. The mean values of the two groups did not differ significantly. A pronounced interindividual variation was found in both groups.

Intravenous labetalol in the treatment of severe hypertension and hypertensive emergencies

The antihypertensive effects of intravenous labetalol were evaluated in 59 patients with hypertensive crises or severe hypertension in need of rapid lowering of blood pressure in a multicenter study. Patients appearing with a supine diastolic blood pressure 125 mm Hg or greater, or a supine systolic blood pressure of more than 200 mm Hg received an initial mini-bolus injection (20 mg) of labetalol. This was followed by repeated incremental doses of 20 to 80 mg given at 10 minute intervals to achieve a supine diastolic blood pressure of less than 95 mm Hg or decrease 30 mm Hg or greater, or a satisfactory decrease in systolic blood pressure. Patients were stratified into those who had taken antihypertensive medication within 24 hours and those who had not. The initial mini-bolus injection caused rapid but not abrupt reduction in blood pressure; the baseline mean blood pressure decreased 23/14 mm Hg. Further injections were needed in the majority of patients (mean: 197 mg). The blood pressure reduction after the last dose of labetalol was 55/33 mm Hg. In pretreated patients and in those who had no medication for 24 hours prior to the intravenous labetalol, the response was similar. Heart rate decreased 10 beats per minute in the total population. In patients pretreated with beta-adrenergic blockers, blood pressure response was similar to that in the total group (59/35 versus 55/33 mm Hg), but heart rate remained essentially unchanged. The dose required to achieve the therapeutic effect was less in pretreated patients than in untreated patients, but the duration of action was shorter. No serious adverse effects were encountered even in patients with concomitant diagnoses of acute left ventricular failure, myocardial infarction, stable congestive heart failure, atrial fibrillation, angina pectoris, acute stroke, transient ischemic attack or encephalopathy. Labetalol is a safe and effective treatment for a rapid blood pressure reduction in hypertensive emergencies.

Labetalol: a review of its pharmacology, pharmacokinetics, clinical uses and adverse effects

Labetalol is a combined alpha- and beta-adrenoceptor blocking agent for oral and intravenous use in the treatment of hypertension. It is a nonselective antagonist at beta-adrenoceptors and a competitive antagonist of postsynaptic alpha 1-adrenoceptors. Labetalol is more potent at beta that at alpha 1 adrenoceptors in man; the ratio of beta-alpha antagonism is 3:1 after oral and 6.9:1 after intravenous administration. Labetalol is readily absorbed in man after oral administration, but the drug, which is lipid soluble, undergoes considerable hepatic first-pass metabolism and has an absolute bioavailability of approximately 25%. There are no active metabolites, and the elimination half-life of the drug is approximately 6 hours. Unlike conventional beta-adrenoceptor blocking drugs without intrinsic sympathomimetic activity, labetalol, when given acutely, produces a decrease in peripheral vascular resistance and blood pressure with little alteration in heart rate or cardiac output. However, like conventional beta-blockers, labetalol may influence the renin-angiotensin-aldosterone system and respiratory function. Clinical studies have shown that the antihypertensive efficacy of labetalol is superior to placebo and to diuretic therapy and is at least comparable to that of conventional beta-blockers, methyldopa, clonidine and various adrenergic neuronal blockers. Labetalol administered alone or with a diuretic is often effective when other antihypertensive regimens have failed. Studies have shown that labetalol is effective in the treatment of essential hypertension, renal hypertension, pheochromocytoma, pregnancy hypertension and hypertensive emergencies. In addition, preliminary studies indicate that labetalol may be of value in the management of ischemic heart disease. The most troublesome side effect of labetalol therapy is posture-related dizziness. Other reported side effects of the drug include gastrointestinal disturbances, tiredness, headache, scalp tingling, skin rashes, urinary retention and impotence. Side effects related to the beta-adrenoceptor blocking effect of labetalol, including asthma, heart failure and Raynaud's phenomenon, have been reported in rare instances.

Blood pressure, body fluid volumes and glomerular filtration rate during treatment with labetalol in essential hypertension

1 In a single blind study seventeen patients with mild or moderate essential hypertension and normal renal function were treated with labetalol alone in increasing doses from 300 via 600 to 1200 mg daily. 2 Average supine BP (systolic/diastolic) was reduced by 24/19 mm Hg. Seven patients attained a diastolic BP less than or equal to Hg. A significant postural fall in systolic BP was recorded, but no symptomatic orthostatic hypotension occurred. 3 In twelve patients measurements of plasma volume (125I-albumin), extracellular volume (82Br-space) and glomerular filtration rate (51Cr-EDTA clearance) on placebo and subsequently labetalol showed no systemic changes. 4 Side effects were few causing two withdrawals because of impotence and arthralgia. 5 It is concluded that monotherapy with labetalol results in clinically relevant, persistent and dose dependent reduction in BP in patients with mild or moderate essential hypertension, apparently without concomitant expansion of body fluid volumes or influence on glomerular filtration rate.