BACKGROUND: Hypertension is a chronic condition associated with an increased risk of mortality and morbidity. The renin-angiotensin-aldosterone system is an important target site for five antihypertensive drug classes: beta blockers, renin inhibitors, ACE inhibitors, angiotensin receptor blockers (ARBs) and aldosterone inhibitors. Renin is the enzyme responsible for converting angiotensinogen to angiotensin I, which is then converted to angiotensin II. Renin inhibitors prevent the formation of both angiotensin I and angiotensin II . Renin inhibitors do not affect kinin metabolism and may produce fewer adverse effects than ACE inhibitors such as dry cough or angioedema. OBJECTIVES: To quantify the dose-related blood pressure lowering efficacy of renin inhibitors versus placebo in the treatment of primary hypertension. SEARCH STRATEGY: We searched the following databases for randomised, double blind, placebo-controlled trials of renin inhibitors: Medline (1966-March 2008), EMBASE (1988-March 2008), Cochrane CENTRAL, and bibliographic citations from retrieved references. No language restrictions were applied. SELECTION CRITERIA: Study design had to meet the following criteria: double-blinded, placebo-controlled; random allocation to a specific dose of renin inhibitor group and parallel placebo group; duration of follow-up of at least three weeks. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and assessed trial quality using risk of bias tables. Disagreements were resolved by discussion or a third reviewer. Data synthesis and analyses were done using the Cochrane Review Manager software, RevMan 5. Data for continuous variables were combined using a weighted mean difference method. Dichotomous variables were analysed using relative risk. MAIN RESULTS: Six trials (N=3694) met the inclusion criteria for this review. Aliskiren was the only renin inhibitor studied in these studies. The meta-analysis shows that aliskiren has a dose-related both systolic/diastolic blood pressure lowering effect as compared to placebo: aliskiren 75 mg -2.9/-2.3 mmHg, aliskiren 150 mg -5.5/-3.0 mmHg, aliskiren 300 mg -8.7/-5.0, aliskiren 600 mg -11.4/-6.6 mmHg. Aliskiren 300 mg significantly lowered both SBP and DBP as compared to aliskiren 150 mg (SBP:-2.97 (95% CI -3.99, -1.95) and DBP: -1.66 (95% CI -2.32, -1.0). Aliskiren has no effect on blood pressure variability. No data was available to assess the effect of aliskiren on heart rate and pulse pressure. This review found weak evidence that with short- term use, aliskiren does not increase withdrawals due to adverse effects as compared to placebo. AUTHORS' CONCLUSIONS: Aliskiren has a dose-related blood pressure lowering effect better than placebo. This effect is similar to that determined for ACE inhibitors and ARBs.
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