Rasagiline, Parkinson neuroprotection, and delayed-start trials

Abstract

Rasagiline has been studied as a Parkinson disease (PD) neuroprotective agent in 2 major clinical trials, utilizing the delayed-start design in an attempt to separate symptomatic drug benefits from a disease-modifying effect. The ostensibly positive outcomes of these studies, however, are obscured by potential confounding factors that seem intrinsic to this trial design, including 1) very small changes in clinical outcome measures that could easily be overshadowed by other influences; 2) probable incomplete blinding to study end; 3) subjective components of the Unified Parkinson's Disease Rating Scale (UPDRS) scoring system; and 4) practice influences from repeated scoring. Interpretation of the recent Attenuation of Disease Progression with Azilect Given Once-daily (ADAGIO) trials is especially problematic given 1) divergent results with the 2 symptomatically beneficial doses and 2) variability in UPDRS scores with active rasagiline, which was twice the magnitude of the major finding of the study. These studies further illustrate the difficulty in documenting a disease-modifying effect when considering a PD drug with symptomatic benefit.