Levodopa therapy for Parkinson's disease: Pharmacokinetics and pharmacodynamics.

For all its imperfections at treating Parkinson's disease (PD), orally-administered levodopa (l-dopa) can be regarded as the "platinum" standard of PD therapeutics for its impact on disability and discomfort and its cost-effectiveness. The past half-century has confirmed that the typical l-dopa-treated patient gains improvement for most Parkinsonian features, presumably by conversion of this amino acid into dopamine in the striatum. However, fundamental questions remain as to its full mechanism of action and how adverse reactions evolve. Various aspects of clinical phenomenology associated with chronic l-dopa use (such as dyskinesias and the long-duration anti-Parkinsonian response) present a continuing challenge for better understanding of its pharmacology. The pharmacokinetics of l-dopa tend to predict some of problems that can emerge during chronic therapy, which can be linked with its irregular uptake and marked dose-by-dose variability in plasma concentrations. Several new pharmaceutical approaches are targeted at the unique physiology of l-dopa uptake and are likely to improve the consistency of its anti-Parkinsonian effect.