Which medicine is most appropriate to add to Mr R's carbidopa/levodopa regimen to reduce 'off' periods?

Which medicine is most appropriate to add to Mr R's carbidopa/levodopa regimen to reduce 'off' periods?

• A. Entacapone
• B. Selegiline
• C. Rasagiline
• D. Pramipexole

Answer: (A)

Wearing-off with levodopa happens because the drug’s effect wanes before the next dose. The best way to address this when a patient is already on carbidopa/levodopa is to add a COMT inhibitor. Entacapone blocks the peripheral enzyme COMT, preventing levodopa from being broken down before it reaches the brain. This increases and prolongs the amount of levodopa that gets into the brain each dose, lengthening on-time and reducing the off periods. Other options act through different mechanisms. MAO-B inhibitors (like selegiline or rasagiline) slow brain dopamine breakdown but don’t directly extend the peripheral availability of levodopa, so their impact on wearing-off is less pronounced. A dopamine agonist (pramipexole) can help, but it introduces additional dopaminergic stimulation and potential side effects, and isn’t as targeted to prolong levodopa’s effect as a COMT inhibitor. So the most appropriate addition to reduce off time in this scenario is entacapone.

Wearing-off with levodopa happens because the drug’s effect wanes before the next dose. The best way to address this when a patient is already on carbidopa/levodopa is to add a COMT inhibitor. Entacapone blocks the peripheral enzyme COMT, preventing levodopa from being broken down before it reaches the brain. This increases and prolongs the amount of levodopa that gets into the brain each dose, lengthening on-time and reducing the off periods.

Other options act through different mechanisms. MAO-B inhibitors (like selegiline or rasagiline) slow brain dopamine breakdown but don’t directly extend the peripheral availability of levodopa, so their impact on wearing-off is less pronounced. A dopamine agonist (pramipexole) can help, but it introduces additional dopaminergic stimulation and potential side effects, and isn’t as targeted to prolong levodopa’s effect as a COMT inhibitor.

So the most appropriate addition to reduce off time in this scenario is entacapone.