A Real-Life Search for the Optimal Set of Conversion Factors to Levodopa-Equivalent-Dose in Parkinson's Disease Patients on Polytherapy

Levodopa Dose Equivalency in Parkinson's Disease: Updated Systematic Review and Proposals

BACKGROUND

To compare drug regimens across clinical trials in Parkinson's disease (PD) conversion formulae between antiparkinsonian drugs have been developed. These are reported in relation to levodopa as the benchmark drug in PD pharmacotherapy as 'levodopa equivalent dose' (LED). Currently, the LED conversion formulae proposed in 2010 by Tomlinson et al. based on a systematic review are predominantly used. However, new drugs with established and novel mechanisms of action and novel formulations of longstanding drugs have been developed since 2010. Therefore, consensus proposals for updated LED conversion formulae are needed.

OBJECTIVES

To update LED conversion formulae based on a systematic review.

METHODS

The MEDLINE, CENTRAL, and Embase databases were searched from January 2010 to July 2021. Additionally, in a standardized process according to the GRADE grid method, consensus proposals were issued for drugs with scarce data on levodopa dose equivalency.

RESULTS

The systematic database search yielded 3076 articles of which 682 were eligible for inclusion in the systematic review. Based on these data and the standardized consensus process, we present proposals for LED conversion formulae for a wide range of drugs that are currently available for the pharmacotherapy of PD or are expected to be introduced soon.

CONCLUSIONS

The LED conversion formulae issued in this Position Paper will serve as a research tool to compare the equivalence of antiparkinsonian medication across PD study cohorts and facilitate research on the clinical efficacy of pharmacological and surgical treatments as well as other non-pharmacological interventions in PD. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The clinical meaning of levodopa equivalent daily dose in Parkinson's disease

Levodopa (L-dopa) remains the basis of pharmacological treatment of Parkinson's disease (PD). However, L-dopa therapy is associated with the development of complications and presents major challenges in the long-term treatment. Thus, other medications may be suggested to delay and/or reduce the doses of L-dopa in order to prevent complications. The interpretation of treatment evolution reported in clinical trials on PD may be tricky, especially due to some variability in medications and dose regimens. Some authors have suggested a conversion factor to generate a total L-dopa equivalent daily dose (LEDD), calculated as a sum of each parkinsonian medication. Therefore, LEDD provides an artificial summary of the total daily medication a patient is receiving, and to date, there is no report focusing on the clinical interpretation of this parameter. Thus, based on a 3-year, multi-center retrospective study assessing the impact of second-line therapy initiation on LEDD in PD patients, the aim of our article was to discuss LEDD as a quantitative outcome to estimate the impact of second-line therapies on medication regimens; and in the second part of the discussion, to provide a narrative review of the clinical outcomes associated with LEDD in the literature.