Abstracts and Citations

Abstract

A, Lines CR, Winner P, Shapiro RE. Age effects on placebo response rates in clinical trials of acute agents for migraine: Pooled analysis of rizatriptan trials in adults. Cephalalgia. 2009;29:711-718.This study examined the effect of age on placebo response rates in rizatriptan trials in adults. Data from 8 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-hour pain relief (reduction to mild or none) and 2-hour 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-byage interaction was significant for pain relief (P < .001) and pain freedom (P = .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.Comments: Although the efficacy of 5-HT1B/1D receptor agonists (triptans) for the acute treatment of migraine attacks in adults is well established, the response to triptans in patients <18 years old is less clear. Many of the initial trials of triptans in children and adolescents failed to demonstrate an advantage over placebo.Various explanations have been proposed, including the relatively short duration of migraine attacks, delays in accessing treatment, study design issues, and pharmacokinetic or pharmacodynamic differences. A common observation in adolescent/pediatric migraine studies has been that whereas drug response rates tend to be similar to those seen in adults, placebo response rates tend to be higher, thereby leading to a lack of separation between drug and placebo. Within the adolescent/pediatric group an inverse relationship between placebo response rate and age has been demonstrated. 1,2 In triptan trials in adults, formulation has been demonstrated to impact placebo response, but it is currently not clear whether an age-related effect on placebo response rates exists. 3 To investigate this issue, Tony Ho et al performed a post hoc analysis of placebo data from pooled phase III adult clinical trials (>5000 patients) with rizatriptan. The results suggest that age was an important predictor of placebo response, with younger adult patients being more likely to respond to placebo. The authors proposed the high placebo response rate observed in adolescents and children represents one end of a continuum which extends into adulthood. A second analysis of drug response vs age documented an effect of age on drug re...