Drug interactions
Cimetidine + Irinotecan
Severity: Minor
Cimetidine and Irinotecan: 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
Irinotecan is activated by carboxylesterases and its active metabolite SN-38 is inactivated by UGT1A1, while CYP3A4 forms inactive metabolites. Cimetidine's weak CYP3A4 inhibition could shift metabolism, but the effect is uncertain.
What this interaction means in plain words
Cimetidine and Irinotecan have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Cimetidine belongs to Gastrointestinal Tract; Irinotecan belongs to Oncology.
Why it happens
Possible weak CYP3A4 inhibition by cimetidine; clinical effect on irinotecan or SN-38 exposure is not established.
What to do
No routine adjustment; monitor for diarrhea and neutropenia as usual during irinotecan therapy.
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 Cimetidine
- Cimetidine + Dofetilide Contraindicated
- Cimetidine + Fezolinetant Contraindicated
- Alfentanil + Cimetidine Major
- Atazanavir + Cimetidine Major
- Carmustine + Cimetidine Major
- Cimetidine + Citalopram Major
Other interactions of Irinotecan
- Clozapine + Irinotecan Contraindicated
- Irinotecan + Sacituzumab govitecan Contraindicated
- Adenovirus types 4 and 7 live + Irinotecan Major
- Apalutamide + Irinotecan Major
- Atazanavir + Irinotecan Major
- Carbamazepine + Irinotecan Major
Frequently asked questions
Can I take Cimetidine with Irinotecan?
MediHelp rates the interaction as minor. Cimetidine and Irinotecan have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Irinotecan is activated by carboxylesterases and its active metabolite SN-38 is inactivated by UGT1A1, while CYP3A4 forms inactive metabolites. Cimetidine's weak CYP3A4 inhibition could shift metabolism, but the effect is uncertain.
How serious is the interaction between Cimetidine and Irinotecan?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: No routine adjustment; monitor for diarrhea and neutropenia as usual during irinotecan therapy.
What other medicines interact with Cimetidine?
MediHelp also lists interactions of Cimetidine with, for example, Dofetilide, Fezolinetant, Alfentanil. The full list is on the Cimetidine page.
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