Maximizing the benefit of pharmacotherapy in Parkinson's disease

Community and Long-Term Care Management of Parkinson???s Disease in the Elderly

Parkinson's disease affects up to 1 million people in the US, most of them elderly. Motor and non-motor symptoms can be significantly disabling to the point of necessitating institutionalisation. Age-related changes in drug absorption, distribution, metabolism and excretion complicate the treatment of elderly patients with Parkinson's disease. General management principles include initiation of medication at low doses with gradual titration based on clinical effects, avoidance of certain classes of drugs (e.g. anticholinergics), and attention to polypharmacy and its risk for potentially toxic drug interactions. Levodopa remains the most efficacious anti-Parkinson's disease medication and should be the cornerstone of therapy in the elderly Parkinson's disease patient. Use of dopamine receptor agonists, amantadine and anticholinergic drugs in the elderly is limited by high risk for psychotoxicity. Catechol-O-methyltransferase inhibitors may be used to augment levodopa in the setting of 'wearing off' (i.e. motor fluctuations). Monoamine oxidase type B (MAO-B) inhibitors can be used across the spectrum of disease severity, but selegiline (deprenyl), the prototype in this class, is characterised by low and erratic bioavailability of the parent drug and conversion to amphetamine metabolites that may increase the risk of adverse events. A new orally disintegrating tablet formulation overcomes some of these limitations. Rasagiline is a new, selective, second-generation MAO-B inhibitor that is chemically and metabolically distinct from selegiline. The favourable safety profile of rasagiline in the elderly and its once-daily formulation may maximise drug adherence and improve outcomes.

Concurrent administration of donepezil HCl and levodopa/carbidopa in patients with Parkinson's disease: assessment of pharmacokinetic changes and safety following multiple oral doses

AIM

The use of acetylcholinesterase inhibitors for the treatment of comorbid Alzheimer's disease in Parkinson's disease (PD) patients stabilized on a levodopa regimen may potentially disrupt cholinergic balance. This randomized, double-blind, crossover study investigated the safety of, and possible drug-drug interaction between, donepezil HCl and levodopa/carbidopa.

METHODS

Twenty-five patients with PD who were taking physician-optimized doses of levodopa/carbidopa (with daytime dosing intervals of 4-8 h) were administered once-daily doses of either donepezil HCl (5 mg) or placebo for 15 days, in two treatment periods, separated by a washout of at least 2 weeks. Some patients took a second dose of levodopa/carbidopa after 4 h, therefore subanalysis of the levodopa/carbidopa data was conducted up to 4 h and 8 h after dosing. Twenty-six healthy matched controls received open-label donepezil HCl only, for a single 15-day period. Blood samples were collected before, during and after the 15 doses of donepezil HCl for pharmacokinetic (PK) assessments. Pharmacokinetic parameters included maximum attained plasma drug concentration (C(max)), time at which C(max) is attained (t(max)), plasma drug concentration at steady state (C(ss)), and area under the drug concentration-time curve over the dosing interval. Safety assessments included monitoring adverse events, and the Unified Parkinson's Disease Rating Scale (UPDRS) motor examination.

RESULTS

The mean age of all subjects was 72.6 +/- 1.3 years. Donepezil PK assessments of PD patients receiving levodopa/carbidopa were similar to the PK results from healthy controls who received donepezil HCl only (mean AUC(0-12 h)= 281.6 +/- 17.6 and 268.6 +/- 19.9 ng.h ml(-1), respectively). Carbidopa PK were not significantly altered by the concomitant administration of multiple doses of donepezil HCl, compared with when PD patients received placebo (mean AUC(0-8 h)= 921.8 +/- 160 and 821.8 +/- 113 ng.h ml(-1), respectively). Four hours after administration of donepezil HCl in PD patients, AUC(0-4 h), C(max) and C(ss) of levodopa were higher than when PD patients received placebo (P < 0.05). Eight hours after donepezil HCl, however, only C(max) and t(max) were observed to change compared with when PD patients received placebo (mean C(max) = 2652 +/- 429 and 2077 +/- 276 ng ml(-1), respectively; mean t(max) = 1.7 +/- 0.4 and 2.9 +/- 0.5 h, respectively; P< or = 0.05). The number of PD patients who experienced at least one adverse event during the study (13/25) was higher when they received donepezil HCl than when they received placebo (5/25), but was the same as healthy subjects who received donepezil HCl only (13/26). There were no significant differences in change from baseline on the UPDRS motor examination parameters in PD patients when they took donepezil HCl and when they took placebo.

CONCLUSIONS

No clinically significant drug-drug interactions between donepezil HCl and levodopa/carbidopa were observed at steady state. The small changes in the pharmacokinetics of levodopa did not result in any change in motor symptoms. Co-administration of the two drugs led to a small increase in adverse events compared with administration of levodopa/carbidopa alone in PD patients. These adverse events, however, were consistent with donepezil's cholinomimetic effect, and their incidence was comparable to that observed following the administration of donepezil HCl alone.