Drug interactions
Irinotecan + St john's wort
Severity: Major
Irinotecan and St john's wort: major interaction.
Last updated Sources: US FDA label
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
St John's wort induces CYP3A4 and substantially reduces SN-38 exposure. This may reduce the antitumour effect of irinotecan.
What this interaction means in plain words
Irinotecan and St john's wort can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Why it happens
St John's wort induces CYP3A4 and P-glycoprotein, increasing irinotecan clearance.
What to do
Avoid St John's wort in patients receiving irinotecan, and stop it at least two weeks before starting treatment. After it is stopped, watch for increased irinotecan toxicity as induction wears off.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
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 Irinotecan with St john's wort?
MediHelp rates the interaction as major. Irinotecan and St john's wort can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. St John's wort induces CYP3A4 and substantially reduces SN-38 exposure. This may reduce the antitumour effect of irinotecan.
How serious is the interaction between Irinotecan and St john's wort?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid St John's wort in patients receiving irinotecan, and stop it at least two weeks before starting treatment. After it is stopped, watch for increased irinotecan toxicity as induction wears off.
What other medicines interact with Irinotecan?
MediHelp also lists interactions of Irinotecan with, for example, Clozapine, Sacituzumab govitecan, Adenovirus types 4 and 7 live. The full list is on the Irinotecan page.
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