OBJECTIVE: To determine if future studies of coenzyme Q10 and GPI-1485 in Parkinson disease (PD) may be warranted. METHODS: We conducted a randomized, double-blind, calibrated futility clinical trial of coenzyme Q10 and GPI-1485 in early untreated PD using placebo data from the DATATOP study to establish the futility threshold. RESULTS: The primary outcome measure (change in total Unified Parkinson's Disease Rating Scale scores over 1 year) did not meet the prespecified criteria for futility for either agent. Secondary analyses using calibration controls and other more recent placebo data question the appropriateness of the predetermined definition of futility, and suggest that a more restrictive threshold may be needed. CONCLUSIONS: Coenzyme Q10 and GPI-1485 may warrant further study in Parkinson disease, although the data are inconsistent. Additional factors (cost, availability of other agents, more recent data on placebo outcomes, other ongoing trials) should also be considered in the selection of agents for Phase III studies. ©2007 AAN Enterprises, Inc.