Using beta blockers as second-line drug therapy for hypertension patients can reduce blood pressure by 30 percent, if dosage is doubled, according to research published in the current issue of The Cochrane Library.
The cause of hypertension is often multifactorial. Therefore, the "pharmacological rationale for combining two drugs of different classes is that by working at a separate site, interference with different effector pathways can be achieved," the authors wrote.
Jenny M.H. Chen, BSc, of the pharmacology and therapeutics department at the University of British Columbia in Vancouver, Canada, and colleagues examined 20 clinical trials involving 3,744 patients to measure the effect beta-blocker therapy had on systolic blood pressure, diastolic blood pressure and heart rate.
Of the 20 studies, 12 added a beta blocker to a thiazide diuretic, while three added a beta blocker to a thiazide diuretic/potassium sparing diuretic combination pill. The other five studies added a beta blocker to a dihydropyridine calcium-channel blocker (CCB).
Trial participants had an average age of 53, were hypertensive and a baseline blood pressure of 158/102 mmHg.
For any hypertensive drugs, researchers found a linear relationship between the dosage of second-line beta blockers and the reduction in blood pressure. At one-quarter the manufacturer’s recommended dose, systolic blood pressure was reduced by -2.9 mmHg and diastolic by -1.4 mmHg. At eight times the recommended dose, reductions were -10.2 mmHg in systolic and -8.8 mmHg in diastolic blood pressure.
When broken down to individual blood pressure drugs, researchers found the blood pressure lowering effect of beta blockers (at one-quarter to one-half the recommended starting dose) was greater when combined with a CCB then with a thiazide. However, the blood pressure lowering effects were similar at starting doses and higher, and in one comparison was lower.
Researchers found that second-line beta blockers reduced resting heart rate by 10 beats per minute, did not affect blood pressure variability and had no effect on pulse pressure.
Chen and colleagues compared the current assessment to a previous review -- published in the Cochrane Database of Systematic Reviews on Oct. 7, 2009 -- which examined the efficacy of diuretics as a second-line therapy. In comparison, while use of second-line beta blockers as therapy reduced diastolic blood pressure to a greater extent than second-line thiazide diuretics, reductions in systolic blood pressure rates were similar.
"We feel that these findings are generalizable to most patients being treated for hypertension where a beta blocker is added as a second-line drug to a first-line thiazide," said Chen.
According to the authors, the limitations in the study stem from not providing estimations of the effect of the addition of a beta blocker to antihypertensive drug classes other than thiazides and CCBs.
The authors noted that “more systemic reviews are urgently needed” to compare and confirm these report findings. Currently, two reviews to examine the efficacy of renin-angiotensin-aldosterone system drugs and CCBs as second-line therapy are underway.