Labetalol, an alpha- and beta-adrenoceptor-blocking agent: its use in therapeutics. A summary of the symposium

Labetalol for hypertension in pregnancy

INTRODUCTION

Labetalol is one of the most commonly used antihypertensive medications for the treatment of hypertension during pregnancy, an increasingly common and leading cause of maternal mortality and morbidity worldwide.

AREAS COVERED

The literature reviewed included the 2014 Canadian national pregnancy hypertension guideline and its references. The additional published literature was retrieved through searches of Medline, CINAHL, and The Cochrane Library using appropriate controlled vocabulary (e.g., pregnancy, hypertension, pre-eclampsia, pregnancy toxemias) and key words (e.g., diagnosis, evaluation, classification, prediction, prevention, prognosis, treatment, and postpartum follow-up).Results were restricted to systematic reviews, randomized controlled trials, controlled clinical trials, and observational studies published in French or English, Jan-Mar/14. The unpublished literature was identified by searching websites of health technology assessment and health technology-related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies. We evaluated the impact of interventions on substantive clinical outcomes for mothers and babies.

EXPERT OPINION

Labetalol is a reasonable choice for treatment of severe or non-severe hypertension in pregnancy. However, we should continue our search for other therapeutic options.

Interaction of clonidine and labetalol in hypertension

Concomitant administration of the alpha 2-adrenoceptor agonist, clonidine, and the alpha 1- and non-selective beta-adrenoceptor antagonist, labetalol, was studied in 12 hypertensive outpatients treated with thiazide diuretics. Clonidine, 0.15 mg b.i.d., effectively lowered supine, standing and isometric blood pressure values when administered to patients on cyclothiazide, 2.5 mg q.d. Addition of labetalol, 200 mg b.i.d., to the diuretic-clonidine treatment resulted in further reduction of blood pressure at rest both in the supine and standing position. In contrast, during isometric work, addition of labetalol to the diuretic-clonidine regimen did not exhibit the same additive antihypertensive effect. When clonidine was given in a dose of 0.3 mg once daily in the evening and the other two drugs as previously, the same antihypertensive effect was observed in the afternoon. Labetalol did not provoke new side-effects of its own.

Factors that contribute to resistant forms of hypertension. Pharmacological considerations

Treatment failure may be caused by induction of compensatory mechanisms that compromise effectiveness of the antihypertensive regimen. Antihypertensive agents have been classified according to mechanism of action, and compensatory mechanisms usually evoked by each class of drugs have been reviewed. Host factors may be responsible for the inability to control blood pressure or may predict special sensitivity or contraindication to a particular class of antihypertensive agents. Recommendations have been made for modification of stepped-care regimens and selection of initial antihypertensive agents based on host factors. Experimental evidence suggests the ability to target antihypertensive therapy in a manner that will prevent or reverse specific end-organ damage. Clinical studies are needed to define the long-term benefit derived from aggressive target organ protection.

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.