A 62-year-old man presents with a 3-year history of progressive bradykinesia, resting tremor, and rigidity. He is newly diagnosed with Parkinson disease and has no cognitive impairment or motor complications. What is the drug of choice for initiating monotherapy in this patient?

Explanation

## First-Line Monotherapy in Early Parkinson Disease ### Clinical Context In a 62-year-old patient with newly diagnosed Parkinson disease (PD), no cognitive impairment, and no motor complications, the choice of initial monotherapy is guided by age, functional disability, and risk of motor complications. **Key Point:** Levodopa/carbidopa is the most efficacious drug for symptomatic control in PD and is the preferred first-line agent in patients aged ≥60 years. Dopamine agonists (DAs) are generally reserved for younger patients (typically <50–55 years) to delay levodopa exposure and reduce the long-term risk of dyskinesias and motor fluctuations. ### Drug Comparison for Early PD Monotherapy | Drug | Mechanism | Advantage | Disadvantage | Preferred Age Group | |------|-----------|-----------|--------------|---------------------| | **Levodopa/carbidopa** | Dopamine precursor | Most efficacious, rapid symptom relief, well-tolerated | Motor complications with long-term use | ≥60 years or significant disability | | **Ropinirole** (DA) | D2/D3 agonist | Delays levodopa, fewer early motor complications | Lower efficacy, somnolence, impulse control disorders | <50–55 years, mild disability | | **Selegiline** | MAO-B inhibitor | Mild symptom relief, theoretical neuroprotection | Weak as monotherapy, amphetamine metabolites | Adjunctive only | | **Amantadine** | NMDA antagonist | Mild benefit, useful for dyskinesias | Weak as monotherapy, tolerance develops | Adjunctive only | ### Why Levodopa/Carbidopa in This Case At age 62 with newly diagnosed PD: - The age threshold for preferring dopamine agonists over levodopa is typically **<50–55 years** (AAN 2017 guideline; Movement Disorder Society recommendations) - At 62 years, levodopa/carbidopa provides **superior symptomatic relief** and is well-tolerated - The risk of developing dyskinesias within a clinically meaningful timeframe is lower in older patients, making levodopa the pragmatic and guideline-supported choice - Carbidopa co-administration reduces peripheral conversion of levodopa, minimizing nausea and cardiovascular side effects **High-Yield:** Per the 2017 AAN guideline and Movement Disorder Society consensus, levodopa/carbidopa is the drug of choice for initial monotherapy in patients ≥60 years with PD. Dopamine agonist monotherapy is preferred only in younger patients (typically <50–55 years) to delay motor complications. **Clinical Pearl:** The "younger patient" threshold for DA preference is often misquoted as <60 years, but current evidence and expert consensus place it closer to <50–55 years. A 62-year-old patient falls clearly in the levodopa-preferred category. ### Rationale for Rejecting Other Options - **Ropinirole:** Preferred in younger patients (<50–55 years); at age 62, the benefit of delaying levodopa does not outweigh the superior efficacy of levodopa/carbidopa - **Selegiline:** Insufficient as monotherapy; used adjunctively to levodopa or as mild early-stage add-on - **Amantadine:** Weak monotherapy; primarily used for managing dyskinesias in advanced PD *Reference: Harrison's Principles of Internal Medicine, 21st ed.; AAN 2017 Practice Guideline for PD; Movement Disorder Society Evidence-Based Medicine Review*