Drug interactions
Fosphenytoin + Loperamide
Severity: Minor
Fosphenytoin and Loperamide: minor 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 (via phenytoin) is an inducer of CYP3A4, CYP2C8 and possibly P-glycoprotein, which may lower systemic loperamide exposure. Reduced loperamide effect on stool frequency is possible, although the clinical significance is modest at usual doses.
What this interaction means in plain words
Fosphenytoin and Loperamide have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Fosphenytoin belongs to Central Nervous System; Loperamide belongs to Gastrointestinal Tract.
Why it happens
Enzyme and possibly P-gp induction by phenytoin increases loperamide metabolism and efflux, lowering its concentrations.
What to do
Monitor antidiarrheal response and titrate loperamide within labeled limits if effect is inadequate; do not exceed the maximum daily dose.
What to ask your pharmacist
- Is there anything I should notice while taking both?
- Do I need to tell my doctor at the next visit?
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Other interactions of Loperamide
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 Loperamide?
MediHelp rates the interaction as minor. Fosphenytoin and Loperamide have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Fosphenytoin (via phenytoin) is an inducer of CYP3A4, CYP2C8 and possibly P-glycoprotein, which may lower systemic loperamide exposure. Reduced loperamide effect on stool frequency is possible, although the clinical significance is modest at usual doses.
How serious is the interaction between Fosphenytoin and Loperamide?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor antidiarrheal response and titrate loperamide within labeled limits if effect is inadequate; do not exceed the maximum daily dose.
What other medicines interact with Loperamide?
MediHelp also lists interactions of Loperamide with, for example, Amiodarone, Amisulpride, Anagrelide. The full list is on the Loperamide page.
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