Drug interactions
Chlorpheniramine + Fosphenytoin
Severity: Minor
Chlorpheniramine and Fosphenytoin: 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 is converted to phenytoin, an inducer of CYP3A4 and other enzymes, which may lower chlorpheniramine concentrations. The antihistamine effect may be reduced, though the clinical impact is probably modest.
What this interaction means in plain words
Chlorpheniramine and Fosphenytoin have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Chlorpheniramine belongs to Respiratory; Fosphenytoin belongs to Central Nervous System.
Why it happens
Induction of CYP3A4 and other hepatic enzymes by phenytoin increases chlorpheniramine clearance.
What to do
Monitor for reduced antihistamine response and increase the dose or change agent if symptoms are not controlled.
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 Chlorpheniramine
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 Chlorpheniramine with Fosphenytoin?
MediHelp rates the interaction as minor. Chlorpheniramine and Fosphenytoin 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 is converted to phenytoin, an inducer of CYP3A4 and other enzymes, which may lower chlorpheniramine concentrations. The antihistamine effect may be reduced, though the clinical impact is probably modest.
How serious is the interaction between Chlorpheniramine and Fosphenytoin?
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 for reduced antihistamine response and increase the dose or change agent if symptoms are not controlled.
What other medicines interact with Chlorpheniramine?
MediHelp also lists interactions of Chlorpheniramine with, for example, Belladonna and opium, Benzhydrocodone / acetaminophen, Brexanolone. The full list is on the Chlorpheniramine page.
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