Tolerability and effectiveness of (S)-amlodipine compared with racemic amlodipine in hypertension: A systematic review and meta-analysis

BACKGROUND: Amlodipine is a calcium channel blocker prescribed for the management of angina and hypertension. As a racemic mixture, amlodipine contains (R)- and (S)-amlodipine isomers, but only (S)-amlodipine as the active moiety possesses therapeutic activity. Based on pharmacologic research, it remains uncertain if (S)-amlodipine alone has similar efficacy and fewer associated adverse events (AEs) compared with the racemic mixtures. OBJECTIVE: The aim of this systematic review and meta-analysis was to determine the effectiveness and tolerability of (S)-amlodipine compared with that of racemic amlodipine. METHODS: A systematic literature search was performed using MEDLINE (1966-2009), EMBASE (1966-2009), the Cochrane Central Register of Controlled Trials (issue 3, 2009), the Chinese Biomedical Database (1978-2009), and the China National Knowledge Internet (1980-2009). All randomized controlled trials (RCTs) comparing (S)-amlodipine 2.5 mg and racemic amlodipine 5.0 mg in the treatment of hypertension were included in the review. The outcome measures to be collected were cardiovascular events, systolic blood pressure (SBP), diastolic BP (DBP), and AEs. Quality assessments of clinical trials were conducted using a modified Jadad Scale, with trials being rated as low quality (score 0-3) or high quality (score 4-7). Meta-analysis of the included studies was performed using RevMan software. RESULTS: Of the 229 references identified, 214 were excluded after screening the titles, abstracts, or full texts. Fifteen RCTs were included, of which 13 were in Chinese and 2 in English. Based on the Jadad Scale score, 3 of the RCTs were classified as high quality (score 5 or 6) and the remaining 12 as low quality (score 1-3). None of the trials evaluated cardiovascular events beyond 40 weeks. Meta-analysis of the 15 trials indicated that (S)-amlodipine was not significantly different from racemic amlodipine in the effect on BP. When only high-quality studies were included, after 4 weeks' treatment, the weighted mean difference (WMD) of SBP and DBP decrease (1 study) was -2.84 (95% CI, -6.42 to 0.74) with (S)-amlodipine and -1.71 (95% CI, -3.48 to 0.06) with racemic amlodipine. After 8 weeks' treatment, the WMD of SBP and DBP decrease (2 studies) was -1.13 (95% CI, -5.29 to 3.03) and -1.34 (95% CI, -2.67 to -0.01), respectively. The risk difference (RD) for the number of patients who experienced AEs with (S)-amlodipine and racemic amlodipine was found to be -0.04 (95% CI, -0.06 to -0.02). When all the trials were included, (S)-amlodipine treatment was associated with significantly less edema than racemic amlodipine (RD, -0.02; 95% CI, -0.03 to 0.00); however, when only high-quality studies (2 studies) were included, no difference was found between the 2 groups (RD, 0.01; 95% CI, -0.02 to 0.03). One high-quality study found significant differences in increases in aspartate and alanine aminotransferase activities in the 2 groups (RD, 0.08; 95% CI, 0.01 to 0.05). No significant differences between the 2 groups were found in the incidence of headache (RD, 0.00; 95% CI, -0.02 to 0.01) or flushing (RD, -0.01; 95% CI, -0.02 to 0.00). CONCLUSIONS: The majority of the clinical trials comparing (S)-amlodipine and racemic amlodipine treatment were low quality (12/15 [80%]). According to the limited evidence, there were no significant differences between (S)-amlodipine 2.5 mg and racemic amlodipine 5.0 mg in controlling BP. When all the trials were considered, (S)-amlodipine treatment was associated with significantly less edema than racemic amlodipine; however, when only high-quality trials were included, no significant difference was found. More long-term, high-quality RCTs with cardiovascular events as the primary outcome are needed to compare the safety and efficacy of (S)-amlodipine and racemic amlodipine.