A Cochrane review included 8 studies with a total of 290 subjects. Two studies examined the effects of captopril, the rest were single trials on single drugs. All comparisons were with placebo. Enalapril was associated with a small increase in the frequency of attacks per week (difference in means 0.8, 95% CI 0.43 to 1.17; 1 study, n=40). The difference between the intervention groups on a subjective improvement score was non-significant. There was a significant effect of buflomedil on the frequency of attacks per week (WMD -8.8, 95% CI -17.55 to -0.09; 1 study, n=31), but there was no evidence of effect on the severity score. Moxisylyte (thymoxamine) also reduced attacks; 19 participants had fewer attacks during the moxisylyte period, 10 during the placebo period and 4 participants had an equal number of attacks in each period (P <0.02, Wilcoxon matched pairs signed rank test; 1 study, n=33). For captopril, beraprost, dazoxiben and ketanserin there was no evidence of an effect on the frequency, severity or duration of attacks. Beraprost (RR 1.62, 95% CI 1.08 to 2.43; 1 study, n=118) and moxisylyte (RR 4.33, 95% CI 1.36 to 13.81; 1 study , n=33) gave significantly more adverse effects than placebo.
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment), by inconsistency (heterogeneity in interventions and outcomes) and by imprecise results (limited study size for each comparison).