Drug interactions
Carbamazepine + Fosphenytoin
Severity: Moderate
Carbamazepine 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, formed from fosphenytoin, and carbamazepine influence each other in an unpredictable way. Carbamazepine concentrations usually fall, while phenytoin levels may rise or fall, risking toxicity or loss of seizure control.
What this interaction means in plain words
Carbamazepine 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.
Carbamazepine belongs to Central Nervous System; Fosphenytoin belongs to Central Nervous System.
Why it happens
Mutual induction of hepatic enzymes including CYP3A4 and CYP2C9/2C19, and possible competition for metabolism.
What to do
Monitor free and total phenytoin and carbamazepine levels when starting, stopping or changing doses. Adjust doses according to levels and clinical response.
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 Carbamazepine
- Artemether / lumefantrine + Carbamazepine Contraindicated
- Cabotegravir + Carbamazepine Contraindicated
- Carbamazepine + Delamanid Contraindicated
- Carbamazepine + Dienogest / estradiol valerate Contraindicated
- Carbamazepine + Doravirine Contraindicated
- Carbamazepine + Elbasvir / grazoprevir Contraindicated
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 Carbamazepine with Fosphenytoin?
MediHelp rates the interaction as moderate. Carbamazepine 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, formed from fosphenytoin, and carbamazepine influence each other in an unpredictable way. Carbamazepine concentrations usually fall, while phenytoin levels may rise or fall, risking toxicity or loss of seizure control.
How serious is the interaction between Carbamazepine 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 free and total phenytoin and carbamazepine levels when starting, stopping or changing doses. Adjust doses according to levels and clinical response.
What other medicines interact with Carbamazepine?
MediHelp also lists interactions of Carbamazepine with, for example, Artemether / lumefantrine, Cabotegravir, Delamanid. The full list is on the Carbamazepine page.
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