Pharmacotherapy for Parkinson's Disease - Observations and Innovations

Abstract: Pharmacotherapy for Parkinson’s disease (PD) is based on levodopa, the most effective dopaminergic drug. The development of motor complications constitutes the major challenge for new or refined therapies.To evaluate the impact of levodopa pharmacokinetics on motor function, an observational study in the patients’ home environment was carried out. A high variability in plasma levodopa levels was found in all patients, irrespective of treatment regimen. The impact of levodopa pharmacokinetics was further studied in a crossover trial comparing sustained-release tablets and continuous daytime intestinal infusion. Infusion produced significantly decreased variability in plasma levels of levodopa, resulting in significantly normalised motor function. A permanent system for long-term levodopa infusion has been developed and 28 patients have been followed for 87 patient-years. Motor response was generally preserved during the long-term observation period, implying that there is no development of tolerance to infusion therapy. Levodopa tablets are normally used in multiples of 50 or 100 mg, thus a rough estimate of individual dosage. A new concept for individualising levodopa/carbidopa doses with microtablets of 5/1.25 mg is under development. An electronic drug-dispensing device for administering the microtablets was tested on patients with PD. All were able to handle the dispenser and most were interested in future use of the concept. Self-assessment of symptoms is accurate in PD, but traditional paper diaries are associated with low compliance. A wireless electronic diary was compared with a corresponding paper diary. The time-stamped and thus completely reliable patient compliance was 88% with the electronic diary.To conclude, pharmacokinetics of levodopa is the major determinant for motor fluctuations in PD. Every effort to individualise dosage and to smooth out the fluctuations in levodopa concentrations should be made, e.g. by means of microtablets or enteral infusion. Electronic patient diaries for real-time data capture are suitable for PD studies.