Dopamine Agonist Treatment of Fluctuating Parkinsonism

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Abstract
• Adjunctive treatment with the very potent and selective dopamine D-2 agonist MK-458 (controlled-release formulation) improved the control of parkinsonism in patients with fluctuating responses to levodopa therapy (with carbidopa). We subsequently switched patients to adjunctive treatment with pergolide, a less potent D-2 agonist. Pergolide therapy controlled parkinsonism more effectively than controlled-release MK-458. Unlike MK-458, pergolide mesylate also has D-1 agonist properties, apparently accounting for its greater antiparkinsonism efficacy. Adjunctive treatment with controlled-release MK-458 elicited less choreiform dyskinesias than either pergolide adjunctive therapy or therapy with carbidopa-levodopa alone; this finding suggests that D-1 receptor stimulation contributes to the elicitation of medication-induced chorea. The highest doses of controlled-release MK-458 resulted in paradoxical freezing of gait in almost one third of patients. This finding suggests that gait freezing, common in untreated parkinsonism, can also be elicited by excessive D-2 stimulation.