The treatment of hypertension by labetalol--a new alpha- and beta-adrenoreceptor blocking agent

Retrospective evaluation of labetalol as antihypertensive agent in dogs

Background

To evaluate the effect on arterial blood pressure (ABP) of labetalol infusion as treatment for perioperative non nociceptive acute hypertension in dogs. The clinical records of dogs receiving intra or postoperative labetalol infusion were retrospectively reviewed. Invasive systolic (SAP), mean (MAP) and diastolic (DAP) arterial pressure and heart rate (HR) before labetalol infusion (T0) and 15, 30, 45 and 60 min (T1, T2, T3 and T4 respectively) after infusion were retrieved. The dose rate of labetalol infusion and use of concurrently administered drugs that could have potentially affected ABP and/or HR were also recorded. ANOVA for repeated measures and Dunnett’s multiple comparison test were used to determine the effect of labetalol on ABP and HR. Differences were considered significant when p < 0.05.

Results

A total of 20 dogs met the inclusion criteria, and hypertension was documented after craniotomy (12/20), adrenalectomy (4/20) and other procedures (4/20). Five dogs received labetalol intraoperatively, 14 postoperatively, and 1 during the surgical procedure and recovery. Median infusion duration and rate were 463 (60-2120) minutes and 1.1 (0.2–3.4) mg/kg/h respectively. Median loading dose was 0.2 (0.2–0.4) mg/kg. Labetalol produced a significant decrease in SAP and DAP at all time points compared to T0 (p < 0.05), while the effect was not significant at T1 for MAP (p = 0.0519). Median maximum MAP decrease was 31 (20–90) mmHg. Heart rate did not increase significantly during treatment (p = 0.2454). Acepromazine given before or during labetalol treatment did not reduce significantly ABP (p = 0.735).

Conclusions

Labetalol produced a reliable and titratable decrease in ABP with non significant increase in HR.

Labetalol (Trandate, Glaxo Inc.; Normodyne, Schering Corp.)

Labetalol is a competitive antagonist of α1-, β1-, and β2-adrenergic receptors. The hemodynamic effects of the drug include reduced blood pressure, heart rate, and peripheral resistance, with little change in resting cardiac output or stroke volume. In open trials and controlled studies, labetalol was an effective antihypertensive. Labetalol compared favorably with β-blockers alone or in combination with vasodilators, for the treatment of hypertension. Reductions in heart rate are less pronounced with labetalol as compared with propranolol. Labetalol produces rapid reductions in blood pressure when administered intravenously for severe hypertension. The most frequent adverse reactions to the drug include fatigue, postural symptoms, headache, and gastrointestinal complaints. Labetalol may prove advantageous when vasodilation in addition to β-blockade is desired, or for selected patients experiencing adverse effects attributable to β-blockade. Until the clinical profile of labetalol is better defined, the use of the drug should be limited.

Treatment Strategies for Paradoxical Hypertension Following Surgical Correction of Coarctation of the Aorta in Children

BACKGROUND

Paradoxical hypertension after repair of coarctation of the aorta is a well-known phenomenon. The pathogenesis involves the activation of the sympathetic nervous system (first phase) and renin-angiotensin system (second phase). Only a limited number of different treatment strategies have been published in the literature, without any comparative studies.

METHODS

Our aim was to describe the current international practice variation surrounding pharmacological treatment currently being employed to treat paradoxical hypertension following the repair of coarctation of the aorta in children. We performed an online survey among 197 members of the Pediatric Cardiac Intensive Care Society. We also conducted a systematic review of the literature regarding the treatment of paradoxical hypertension.

RESULTS

Eighty-eight people (45%), from 62 different centers, responded and answered the questions regarding blood pressure control. Nitroprusside is the first drug of choice for initial blood pressure control in 66% of respondents, esmolol in 11%, labetalol in 11%, and angiotensin-converting enzyme inhibitors (ACEIs) are used by 3% of respondents. For oral blood pressure control after discharge from the pediatric intensive care unit, 75% of respondents use ACEIs, 18% use labetalol, and 12% use other beta-blockers (propranolol, carvedilol, atenolol, metoprolol). The systematic review identified 14 articles reporting pharmacological treatment of direct postoperative hypertension following coarctation repair.

CONCLUSION

There is wide practice variability, due to the lack of sufficient compelling evidence. The majority (66%) of caregivers use nitroprusside to control blood pressure in the acute postoperative phase. The ACEIs are the drug of choice for chronic blood pressure control.

Labetalol. A reappraisal of its pharmacology, pharmacokinetics and therapeutic use in hypertension and ischaemic heart disease

Since labetalol was first reviewed in the Journal (1978), its scope of therapeutic use has expanded and become better defined. Labetalol is an adrenoceptor blocking drug with combined alpha- and beta-blocking properties. These result in a more favourable haemodynamic profile for labetalol compared with 'pure' beta-blockers or pure alpha-blockers, but also contribute to a wider range, but not an overall increased incidence, of adverse effects. The drug is effective and well-tolerated in patients with all grades of hypertension, but is of particular value in special subgroups such as Black patients, the elderly and patients with renal hypertension. While comparative studies are not extensive, available data show that the drug reduces blood pressure to a similar extent, and in a similar proportion of patients, as 'pure' beta-blockers such as propranolol, pure alpha-blockers such as prazosin, calcium antagonists (nifedipine, verapamil), and centrally acting drugs (clonidine and methyldopa). Labetalol is very effective in hypertensive pregnant women and in hypertensive crises, where it provides good control of blood pressure without serious adverse effects, and where few therapeutic options exist. Few controlled studies have investigated the use of labetalol in deliberate induction of hypotension or prevention of hypertension during anaesthesia, and also in patients with ischaemic heart disease. However, available evidence suggests a role for labetalol in these indications and further studies should aid in clarification of its efficacy in these areas. Thus, with its broad scope of therapeutic use in hypertension labetalol remains an important therapeutic option, and the drug may well find an additional place in the treatment of myocardial ischaemia if further evidence confirms encouraging preliminary findings.

Rising multiple-dose pharmacokinetics of labetalol in hypertensive patients

Labetalol, a drug possessing both alpha- and beta-adrenergic blocking activities, is used in the treatment of hypertension. The current study was undertaken to elucidate the steady-state pharmacokinetics of labetalol following a rising oral multiple-dosage regimen. Twelve patients received oral labetalol every 12 hours for 18 days. An initial dose of 100 mg was increased at three-day intervals to 200, 300, 400, and 600 mg q12h. Selected blood samples were taken at various times following drug administration at each dose level and analyzed for labetalol levels by a specific high-performance liquid chromography assay. The pharmacokinetics of labetalol are best described by a two-compartment open model with first-order absorption. The half-lives of the absorption, distribution, and elimination phases are 0.6, 1.3, and 8.3 hours, respectively. The steady-state plasma drug concentrations are predictable from the pharmacokinetic data and are in good agreement with the observed values. Steady-state levels are reached by the third day at each dose level studied and increase proportionally with dose.

Multicenter clinical evaluation of long-term efficacy and safety of labetalol in treatment of hypertension

The long-term efficacy and safety of labetalol, an antihypertensive agent with combined beta- and alpha-blocking activity, were evaluated alone (number = 193) and in combination with a diuretic (number = 144) in an open-label multicenter trial of 337 hypertensive patients aged 21 to 75 years, including initially 205 (61 percent) men and 219 (65 percent) Caucasians. There were 219 (65 percent) mild, 85 (25 percent) moderate, and 33 (10 percent) severe hypertensive patients. Labetalol (100 to 1,200 mg twice a day) alone or in combination with a diuretic reduced the mean standing blood pressure by 13/11 and 25/16 mm Hg to 135/88 and 130/91 mm Hg, respectively (p less than 0.01), and supine blood pressure by 6/7 and 18/13 mm Hg to 141/86 and 138/90 mm Hg (p less than 0.01), respectively. Blood pressure reductions observed at one month were maintained after one year; 206 (62 percent) patients had 10 mm Hg or greater reductions and 184 (56 percent) patients were maintained at diastolic blood pressures less than 90 mm Hg. Most frequently reported drug-related side effects included fatigue (14 percent), dizziness (12 percent), nausea (11 percent), nasal stuffiness (8 percent), headache (4 percent), and male sexual dysfunction (14 percent). Side effects were generally of mild to moderate intensity and often transient. In addition, in 27 (8 percent) patients reversible asymptomatic transaminase elevations to greater than twice normal developed at some time during the study. In 13 (4 percent) patients these alterations resolved during continued labetalol therapy, but in five (2 percent) patients these marked elevations led to discontinuation of the drug. A total of 32 (9.5 percent) patients were terminated prematurely due to side effects (most commonly genitourinary or gastrointestinal) possibly attributable to the drug. These findings indicate that labetalol with or without a diuretic is a potentially effective, safe, and relatively well-tolerated long-term antihypertensive therapy.

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.