Drug interactions
Carbidopa + Phenytoin
Severity: Moderate
Carbidopa and Phenytoin: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Phenytoin has been reported to reduce the benefit of levodopa/carbidopa, so parkinsonian symptoms may return or worsen.
What this interaction means in plain words
Carbidopa and Phenytoin can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Carbidopa belongs to Central Nervous System; Phenytoin belongs to Central Nervous System.
Why it happens
The mechanism is not well established; altered levodopa effect at the central level is proposed.
What to do
Monitor for loss of motor response when phenytoin is started and increase levodopa if needed, or choose another anticonvulsant.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Carbidopa
Other interactions of Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Frequently asked questions
Can I take Carbidopa with Phenytoin?
MediHelp rates the interaction as moderate. Carbidopa and Phenytoin can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Phenytoin has been reported to reduce the benefit of levodopa/carbidopa, so parkinsonian symptoms may return or worsen.
How serious is the interaction between Carbidopa and Phenytoin?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor for loss of motor response when phenytoin is started and increase levodopa if needed, or choose another anticonvulsant.
What other medicines interact with Carbidopa?
MediHelp also lists interactions of Carbidopa with, for example, Metoclopramide, Amlodipine-atorvastatin, Amlodipine-benazepril. The full list is on the Carbidopa page.
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