Drug interactions
Fluconazole + Lapatinib
Severity: Major
Fluconazole and Lapatinib: major interaction.
Last updated Sources: Health Canada product monograph
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
Lapatinib is a CYP3A4 substrate and can prolong the QT interval. Fluconazole inhibits CYP3A4 and also prolongs QT, so combined use may raise lapatinib exposure and arrhythmia risk.
What this interaction means in plain words
Fluconazole and Lapatinib 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.
Fluconazole belongs to Anti Fungals; Lapatinib belongs to Oncology.
Why it happens
CYP3A4 inhibition by fluconazole raises lapatinib levels, with additive QT prolongation.
What to do
Avoid if possible; otherwise consider reducing the lapatinib dose per labeling for strong CYP3A4 inhibitors or the fluconazole dose. Monitor ECG and electrolytes.
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 Fluconazole
- Dihydroergotamine intranasal + Fluconazole Contraindicated
- Dihydroergotamine + Fluconazole Contraindicated
- Dofetilide + Fluconazole Contraindicated
- Domperidone + Fluconazole Contraindicated
- Dronedarone + Fluconazole Contraindicated
- Erythromycin + Fluconazole Contraindicated
Other interactions of Lapatinib
- Dofetilide + Lapatinib Contraindicated
- Ibutilide + Lapatinib Contraindicated
- Lapatinib + Pimozide Contraindicated
- Lapatinib + Saquinavir Contraindicated
- Lapatinib + Thioridazine Contraindicated
- Adagrasib + Lapatinib Major
Frequently asked questions
Can I take Fluconazole with Lapatinib?
MediHelp rates the interaction as major. Fluconazole and Lapatinib 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. Lapatinib is a CYP3A4 substrate and can prolong the QT interval. Fluconazole inhibits CYP3A4 and also prolongs QT, so combined use may raise lapatinib exposure and arrhythmia risk.
How serious is the interaction between Fluconazole and Lapatinib?
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 if possible; otherwise consider reducing the lapatinib dose per labeling for strong CYP3A4 inhibitors or the fluconazole dose. Monitor ECG and electrolytes.
What other medicines interact with Fluconazole?
MediHelp also lists interactions of Fluconazole with, for example, Dihydroergotamine intranasal, Dihydroergotamine, Dofetilide. The full list is on the Fluconazole page.
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