Age Effects on Placebo Response Rates in Clinical Trials of Acute Agents for Migraine: Pooled Analysis of Rizatriptan Trials in Adults

This study examined the effect of age on placebo response rates in rizatriptan trials in adults. Data from eight rizatriptan adult trials involving patients treating moderate/severe migraine attacks with rizatriptan 5 mg (N = 1819), rizatriptan 10 mg (N = 2046) or placebo (N = 1322) were pooled for post hoc analysis. Logistic regression was used to model 2-h pain relief (reduction to mild or none) and 2-h pain freedom rates by treatment groups. Older patients had lower placebo response rates than younger patients; the estimated odds ratio (older vs. younger) for a 10-year age increase was 0.83 for pain relief [95% confidence interval (CI) 0.75, 0.93] and 0.81 for pain freedom (95% CI 0.68, 0.97). The response proportion vs. age trend was flat for rizatriptan 5 mg and slightly increased for rizatriptan 10 mg. The treatment-by-age interaction was significant for pain relief (P < 0.001) and pain freedom (P = 0.001), suggesting an increasing trend of treatment advantage of rizatriptan over placebo as age increased. Age appeared to be an important predictor of placebo response rate in rizatriptan trials, with older patients being less likely to respond to placebo and more likely to respond to rizatriptan.