The Long-duration Response to Levodopa: Phenomenology, Potential Mechanisms and Clinical Implications

The antiparkinsonian response to levodopa is characterized by an immediate motor improvement lasting hours and a more sustained response lasting days. These two responses have been referred to as the short-duration response (SDR) and the long-duration response (LDR). The LDR represents a substantial component of the clinical effect of levodopa and has been clinically recognized for several decades, but it remains poorly understood. This review will focus on the LDR phenomenology and theories about its origin, with the goal of promoting inquiry into this important but as yet poorly understood aspect of levodopa therapy for PD.