Investigation of influencing factors on higher placebo response in East Asian versus Western clinical trials for partial epilepsy: a meta-analysis.

BACKGROUND: Placebo response in clinical trials for anti-epileptic drugs (AEDs) has been examined and a recent meta-analysis revealed that East Asian trials showed unexpectedly higher placebo response. As multi-national trials have become common, it is important to understand placebo response in different settings, including regions/countries for future clinical trials.
OBJECTIVE: The present meta-analysis aims to investigate the potential factors that contribute to higher placebo response in clinical trials for add-on therapy to adult patients with refractory partial epilepsy in East Asian and Western populations.
METHODS: A database was established based on published clinical trials conducted in East Asian and Western countries. The relationship between the degree of placebo response and potential influencing factors was examined by logistic regression analyses.
RESULTS: The database included 33 trials from five AEDs: gabapentin, topiramate, levetiracetam, pregabalin, and zonisamide. Placebo response was associated with patient characteristics such as disease duration, percentage of patients with complex partial seizure (CPS) at baseline, percentage of patients treated with two AEDs, protocol-required seizure frequency at baseline, and year of publication. Logistic regression analysis demonstrated that the placebo response in East Asian trials was statistically higher than that in Western trials.
CONCLUSION: Patient characteristics such as longer disease duration and CPS at baseline contribute to a reduction in placebo response in clinical trials of AEDs for partial epilepsy. While the reasons for the geographical difference in placebo response are not clear, these and other patient characteristics contributing to placebo response should be carefully considered in the design of future clinical trials of AEDs for partial epilepsy.