Drug interactions
Carbidopa-levodopa + Fosphenytoin
Severity: Moderate
Carbidopa-levodopa and Fosphenytoin: 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, the active form of fosphenytoin, has been reported to reduce the benefit of levodopa in Parkinson disease, with worsening of symptoms. The effect is not predictable and the mechanism is unclear.
What this interaction means in plain words
Carbidopa-levodopa and Fosphenytoin 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-levodopa belongs to Central Nervous System; Fosphenytoin belongs to Central Nervous System.
Why it happens
Mechanism not established; possible effects on levodopa pharmacokinetics or pharmacodynamics.
What to do
Monitor parkinsonian symptoms when fosphenytoin is started or stopped. Increase the levodopa dose if the response declines.
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-levodopa
- Carbidopa-levodopa + Isocarboxazid Contraindicated
- Carbidopa-levodopa + Phenelzine Contraindicated
- Carbidopa-levodopa + Selegiline transdermal Contraindicated
- Carbidopa-levodopa + Tranylcypromine Contraindicated
- Amisulpride + Carbidopa-levodopa Major
- Asenapine + Carbidopa-levodopa Major
Other interactions of Fosphenytoin
- Dronedarone + Fosphenytoin Contraindicated
- Fosphenytoin + Ledipasvir-sofosbuvir Contraindicated
- Fosphenytoin + Lorlatinib Contraindicated
- Fosphenytoin + Lurasidone Contraindicated
- Fosphenytoin + Ranolazine Contraindicated
- Fosphenytoin + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
Frequently asked questions
Can I take Carbidopa-levodopa with Fosphenytoin?
MediHelp rates the interaction as moderate. Carbidopa-levodopa and Fosphenytoin 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, the active form of fosphenytoin, has been reported to reduce the benefit of levodopa in Parkinson disease, with worsening of symptoms. The effect is not predictable and the mechanism is unclear.
How serious is the interaction between Carbidopa-levodopa and Fosphenytoin?
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 parkinsonian symptoms when fosphenytoin is started or stopped. Increase the levodopa dose if the response declines.
What other medicines interact with Carbidopa-levodopa?
MediHelp also lists interactions of Carbidopa-levodopa with, for example, Isocarboxazid, Phenelzine, Selegiline transdermal. The full list is on the Carbidopa-levodopa page.
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