Which drug is a direct-acting dopamine receptor agonist?

• A. Ropinirole
• B. Rasagiline
• C. Levodopa
• D. Selegiline

Answer: (A)

Direct-acting dopamine receptor agonists directly stimulate dopamine receptors, mimicking dopamine’s effect without needing to be converted or broken down first. Ropinirole binds to dopamine receptors (especially D2-like receptors such as D2 and D3), providing receptor activation that helps improve motor symptoms in conditions like Parkinson disease. In contrast, MAO-B inhibitors like rasagiline and selegiline prevent the breakdown of dopamine, raising its levels but not directly activating receptors themselves. Levodopa, a dopamine precursor, increases dopamine by supplying the brain with the substrate that gets converted to dopamine, which is an indirect way to boost dopaminergic signaling. Because ropinirole directly activates dopamine receptors, it is the direct-acting dopamine receptor agonist.