Drug interactions
Erythromycin + Fosphenytoin
Severity: Moderate
Erythromycin 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
Fosphenytoin (phenytoin) can induce CYP3A4 and lower erythromycin concentrations, possibly causing loss of antibacterial efficacy. Erythromycin may also raise phenytoin levels in some patients, which can lead to phenytoin toxicity. This is not a true contraindication but needs attention.
What this interaction means in plain words
Erythromycin 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.
Erythromycin belongs to Anti Bacterial; Fosphenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces CYP3A4, increasing erythromycin metabolism, while erythromycin may inhibit phenytoin metabolism.
What to do
Monitor clinical response to erythromycin and consider an alternative antibiotic if treatment fails. Monitor phenytoin levels and for signs of toxicity such as nystagmus and ataxia.
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 Erythromycin
- Conivaptan + Erythromycin Contraindicated
- Dihydroergotamine intranasal + Erythromycin Contraindicated
- Dihydroergotamine + Erythromycin Contraindicated
- Domperidone + Erythromycin Contraindicated
- Dronedarone + Erythromycin Contraindicated
- Droperidol + Erythromycin 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 Erythromycin with Fosphenytoin?
MediHelp rates the interaction as moderate. Erythromycin 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. Fosphenytoin (phenytoin) can induce CYP3A4 and lower erythromycin concentrations, possibly causing loss of antibacterial efficacy. Erythromycin may also raise phenytoin levels in some patients, which can lead to phenytoin toxicity. This is not a true contraindication but needs attention.
How serious is the interaction between Erythromycin 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 clinical response to erythromycin and consider an alternative antibiotic if treatment fails. Monitor phenytoin levels and for signs of toxicity such as nystagmus and ataxia.
What other medicines interact with Erythromycin?
MediHelp also lists interactions of Erythromycin with, for example, Conivaptan, Dihydroergotamine intranasal, Dihydroergotamine. The full list is on the Erythromycin page.
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