Direct-acting dopamine receptor agonists are most effective in the __________ stages of Parkinson's disease.

• A. Early
• B. Mid
• C. Late
• D. End

Answer: (A)

Direct-acting dopamine receptor agonists work by stimulating dopamine receptors directly in the brain, bypassing the need for the neurons to produce or convert dopamine. In the early stages of Parkinson’s disease, enough dopaminergic receptors and pathways remain so this receptor-level stimulation can meaningfully improve motor symptoms and help defer the introduction of levodopa, potentially reducing long-term levodopa–related complications. As the disease advances, more dopaminergic neurons and postsynaptic receptors are lost, making these agents less effective and often harder to titrate without side effects. For that reason, their greatest utility is in the early stages of the disease.