Conversion of L-dopa to Extended Release L-dopa (Rytary®) in Patients with Fluctuating Parkinson's Disease: Predictor's of Dose

Background: A new extended release levodopa capsule (C/L ERC), Rytary® , has demonstrated improved "on" time in fluctuating Parkinson's disease patients, compared to optimally dosed immediate release levodopa. The milligram dosing, however, differs markedly and no empiric ratio or formula for dose conversion currently exists. Objective: To determine the most effective conversion strategy from C/L to C/L ERC. Methods: We reviewed fluctuating PD patients with problematic "off" time who were converted to C/L ERC using a semistructured dose titration schedule, and collected data regarding basic efficacy, tolerability, and dosing, in order to determine an empirically based dose conversion formula. We collected demographics, PD historic data, and other medication use. Results: Eighty fluctuating PD patients were given C/L ERC samples, 68 took at least one dose [46 male (67.6%), age 66.6±10.3 y], and 62 had adequate data for dose convergence calculations. At a mean follow-up of 119±101 days, [Range: 24-355 days], 43/68 (63.3%) remained on C/L ERC. CGI-I of "much improved" or "very much improved" was reported by 27/62 (43.5%) and dyskinesia scores from the Movement Disorder Society Unified Parkinson's Disease Rating Scale item 4.1, (0-4 range)) tended to improve from 0.9±1.1 to 0.5±0.6, P = 0.08. The mean individual daily ratio was 2.0±0.6 : 1, [range 1.0-3.5]. A lower number of baseline daily L-dopa doses predicted a higher conversion ratio, but pre-conversion dyskinesia did not. Conclusions: This retrospective study found that C/L ERC was generally well tolerated and preferred by many patients. The mean total daily conversion ratio is 2 : 1.