Wednesday, October 31, 2007

Are Beta Blockers Effective First-line Treatments for Hypertension?

Are Beta Blockers Effective First-line Treatments for Hypertension?

Cochrane for Clinicians

Putting Evidence into Practice

WILLIAM E. CAYLEY, JR., md, University of Wisconsin Eau Claire Family Medicine Residency, Eau Claire, Wisconsin

Cochrane Abstract

Two recent systematic reviews found first-line beta blockers to be less effective in reducing the incidence of stroke and the combined end point of stroke, myocardial infarction, and death compared with all other antihypertensive drugs taken together. However, beta blockers might be better or worse than a specific class of drugs for a particular outcome measure; therefore, comparing beta blockers with all other classes taken together could be misleading. In addition, these systematic reviews did not assess the tolerability of beta blockers relative to other antihypertensive medications. Thus, we undertook this review to reassess the place of beta blockers as first-line therapy for hypertension compared with other major classes of antihypertensive drugs.

Objectives: To quantify the effectiveness and safety of beta blockers on morbidity and mortality end points in adults with hypertension.

Search Strategy: We searched eligible studies up to June 2006 in the Cochrane Controlled Trials Register, Medline, Embase, and reference lists of previous reviews, and by contacting hypertension experts.

Selection Criteria: We selected randomized controlled trials (RCTs) that assessed the effects of beta blockers compared with placebo, no therapy, or other drug classes (as monotherapy or first-line therapy for hypertension) on mortality and morbidity end points in men and nonpregnant women 18 years or older.

Data Collection and Analysis: At least two authors independently applied study selection criteria, assessed study quality, and extracted data; differences were resolved by consensus. We expressed study results as relative risks (RRs) with 95% confidence intervals (CIs), and conducted quantitative analyses with trial participants in groups to which they were randomly allocated, regardless of which or how much treatment they actually received. In the absence of significant heterogeneity among studies (P > .1), we performed a meta-analysis using a fixed-effects method. Otherwise, we used the random-effects method and investigated the cause of heterogeneity by stratified analysis. In addition, we used the Higgins statistic (I2) to quantify the amount of between-study variability in effect attributable to true heterogeneity rather than chance.

Main Results: Thirteen RCTs (n = 91,561) that met our inclusion criteria compared beta blockers with placebo or no treatment (four trials with 23,613 participants), diuretics (five trials with 18,241 participants), calcium channel blockers (four trials with 44,825 participants), and renin-angiotensin system (RAS) inhibitors (three trials with 10,828 participants). The risk of all-cause mortality was not different between first-line beta blockers and placebo (RR = 0.99; 95% CI, 0.88 to 1.11; I2 = 0 percent); diuretics; or RAS inhibitors, but the risk was higher for beta blockers compared with calcium channel blockers (RR = 1.07; 95% CI, 1.00 to 1.14; I2 = 2.2%; absolute risk increase [ARI] = 0.5 percent; number needed to harm [NNH] = 200).

The risk of total cardiovascular disease was lower for first-line beta blockers compared with placebo (RR = 0.88; 95% CI, 0.79 to 0.97;I2 = 21.4 percent; absolute risk reduction [ARR] = 0.7 percent; number needed to treat [NNT] = 140). This is primarily a reflection of the significant decrease in stroke (RR = 0.80; 95% CI, 0.66 to 0.96; I2 = 0 percent; ARR = 0.5 percent; NNT = 200). Coronary heart disease risk was not significantly different between beta blockers and placebo. The effect of beta blockers on cardiovascular disease was significantly worse than that of calcium channel blockers (RR = 1.18; 95% CI, 1.08 to 1.29; I2 = 0 percent; ARI = 1.3 percent; NNH = 80) but was not significantly different from that of diuretics or RAS inhibitors. Increased total cardiovascular disease was caused by an increase in stroke compared with calcium channel blockers (RR = 1.24; 95% CI, 1.11 to 1.40; I2 = 0 percent; ARI = 0.6 percent; NNH = 180). There was also an increase in stroke with beta blockers compared with RAS inhibitors (RR = 1.30; 95% CI, 1.11 to 1.53; I2 = 29.1 percent; ARI = 1.5 percent; NNH = 65).

Coronary heart disease risk was not significantly different between beta blockers and diuretics or calcium channel blockers or RAS inhibitors. In addition, patients taking beta blockers were more likely to discontinue treatment because of adverse effects than those taking diuretics (RR = 1.86; 95% CI, 1.39 to 2.50; I2 = 78.2 percent; ARI = 6.4 percent; NNH = 16) or RAS inhibitors (RR = 1.41; 95% CI, 1.29 to 1.54; I2 = 12.1 percent; ARI = 5.5 percent; NNH=18); there was no significant difference between beta blockers and calcium channel blockers.

Authors' conclusions: The available evidence does not support the use of beta blockers as first-line drugs in the treatment of hypertension. This conclusion is based on the relatively weak effect of beta blockers to reduce stroke and the absence of an effect on coronary heart disease when compared with placebo or no treatment. More importantly, it is based on the trend towards worse outcomes compared with calcium channel blockers, RAS inhibitors, and thiazide diuretics. Most of the evidence for these conclusions comes from trials in which atenolol (Tenormin) was the beta blocker used (75 percent of participants taking beta blockers in this review). However, it is not known whether beta blockers have differential effects on younger and older patients or whether there are differences among the subtypes of beta blockers.


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