Which Parkinson disease therapy is well established as effective but tends to wear off with long-term use?

• A. Pramipexole/Ropinirole
• B. Selegiline
• C. Carbidopa/Levodopa
• D. Amantadine

Answer: (C)

Levodopa provides the greatest and most reliable improvement of motor symptoms in Parkinson disease because it replenishes brain dopamine by delivering a precursor that can cross into the brain and be converted to dopamine. Carbidopa boosts this effect by preventing peripheral breakdown, so more levodopa reaches the brain and side effects are reduced. This combination is well established as effective, but with long-term use the benefit often wears off before the next dose, and patients can experience dyskinesias at peak effect. The wearing-off arises from the progression of dopaminergic neuron loss and the pulsatile nature of oral levodopa, which leads to fluctuating motor control. Clinicians manage it by adjusting dosing intervals and sometimes adding other agents to smooth dopamine levels or using continuous delivery in advanced cases.