Ask what else the patient is swallowing

Ask every patient on an oral anticancer agent, at every visit, what else they are taking — and ask it as an open question about tablets, powders, syrups, churnas and anything recommended by family, not as a question about medicines. Patients do not classify an ayurvedic preparation or a herbal supplement as a drug, so a closed question about medication returns nothing.

The interactions are real and mostly pharmacokinetic. St John's wort induces CYP3A4 and can reduce exposure to several tyrosine kinase inhibitors substantially. Proton pump inhibitors, often taken without prescription, reduce absorption of the pH-dependent TKIs. Grapefruit and its juice inhibit CYP3A4 in the other direction. Many traditional preparations are of unknown composition, and some carry heavy metals that complicate the interpretation of deranged renal or liver function.

When something is disclosed, the useful response is not prohibition but sequencing and timing where an interaction is manageable, and a clear explanation of why one specific item has to stop. A patient told to stop everything usually stops telling you instead.

• Ask openly about powders, syrups, churnas and family remedies, not about 'medications'
• Ask specifically about antacids and proton pump inhibitors with pH-dependent oral agents
• Check the current oral agent against CYP3A4 inducers and inhibitors before each cycle
• Where composition is unknown, say so plainly rather than guessing at an interaction
• Explain why a specific item must stop; a blanket prohibition ends disclosure

Why it matters

The commonest reason an oral anticancer drug underperforms is not resistance but exposure, and exposure is often being altered by something nobody recorded.

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