A Cochrane review 1 included 10 studies with a total of 1,175 subjects and 4 different alpha blockers. Mean duration of studies was 5.9 weeks, and weighted mean baseline blood pressure of the participants was 155/101 mm Hg. The best estimate of the trough blood pressure lowering efficacy of these drugs was -8/-5 mm Hg.
When the different alpha blockers were compared, there was a remarkable similarity in the trough BP lowering effects of doxazosin (-6.42, 95% CI -10.12 to -2.80 mm Hg for SBP and -3.53, 95% CI -4.99 to -2.07 mm Hg for DBP) and terazosin (-6.59, 95% CI -10.22 to -2.96 mm Hg for SBP and -4.40, 95% CI -5.95 to -2.84 mm Hg for DBP). Although numerically higher, the trough BP lowering effect of prazosin (-10.38, 95% CI -16.21 to -4.56 mm Hg for SBP and -6.90, 95% CI -9.79 to -4.01 mm Hg for DBP) was not significantly different than either doxazosin or terazosin using indirect comparisons. The review did not provide a good estimate of the incidence of harms associated with alpha blockers because of the short duration of the trials and the lack of reporting of adverse effects in many of the trials. An analysis of withdrawals due to adverse effects with alpha blockers was only reported in 4 of the included trials; there was no statistically significant difference versus placebo.
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment) and by potential reporting bias. The authors stated that the magnitude of blood pressure lowering found in the review is probably an overestimate of the true effect.
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