Senile Parkinsonism and dopa pharmacokinetics.

Senile Parkinsonism can be clinically differentiated from idiopathic Parkinson's disease in younger age groups. It has a slower clinical course, an altered therapeutic response and a more widespread neuropathology. The drug of choice for senile Parkinsonism is levodopa given in low starting daily doses of 100mg, with low increments of 100mg every 4 to 7 days and low maintenance doses of 0.5 to 2.5g daily. Increased absorption of a given dose of levodopa in the elderly explains in part the lower dosage requirements. Combined therapy with a peripheral decarboxylase inhibitor is usually unnecessary in the elderly and carries a higher risk of neuropsychiatric toxicity. The use of a peripheral decarboxylase inhibitor should be reserved for those few elderly patients with significant gastrointestinal side effects and for those who respond poorly to levodopa alone. Anticholinergic agents are in general contraindicated in the elderly, either used alone or in combination with levodopa.