Drug interactions
Fosphenytoin + Moxifloxacin
Severity: Moderate
Fosphenytoin and Moxifloxacin: 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
Fluoroquinolones have been associated with both raised and lowered phenytoin concentrations in isolated reports. Fluoroquinolones also lower seizure threshold, which may work against anticonvulsant therapy. Fosphenytoin is converted to phenytoin, so the same concerns apply.
What this interaction means in plain words
Fosphenytoin and Moxifloxacin 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 belongs to Central Nervous System; Moxifloxacin belongs to Anti Bacterial.
Why it happens
Mechanism is not established; variable effects on phenytoin levels plus a pharmacodynamic lowering of seizure threshold by the quinolone.
What to do
Monitor phenytoin concentrations and seizure control when starting or stopping moxifloxacin, and adjust the dose accordingly.
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 Moxifloxacin
- Amiodarone + Moxifloxacin Contraindicated
- Arsenic trioxide + Moxifloxacin Contraindicated
- Disopyramide + Moxifloxacin Contraindicated
- Dofetilide + Moxifloxacin Contraindicated
- Dronedarone + Moxifloxacin Contraindicated
- Droperidol + Moxifloxacin 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 Fosphenytoin with Moxifloxacin?
MediHelp rates the interaction as moderate. Fosphenytoin and Moxifloxacin 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. Fluoroquinolones have been associated with both raised and lowered phenytoin concentrations in isolated reports. Fluoroquinolones also lower seizure threshold, which may work against anticonvulsant therapy. Fosphenytoin is converted to phenytoin, so the same concerns apply.
How serious is the interaction between Fosphenytoin and Moxifloxacin?
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 phenytoin concentrations and seizure control when starting or stopping moxifloxacin, and adjust the dose accordingly.
What other medicines interact with Moxifloxacin?
MediHelp also lists interactions of Moxifloxacin with, for example, Amiodarone, Arsenic trioxide, Disopyramide. The full list is on the Moxifloxacin page.
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