Drug interactions
Lapatinib + Sulfamethoxazole
Severity: Moderate
Lapatinib and Sulfamethoxazole: moderate 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
Both lapatinib and sulfamethoxazole (usually given with trimethoprim) have been associated with QT interval prolongation. Combined use may add to the risk of arrhythmia, particularly with electrolyte disturbance or heart disease.
What this interaction means in plain words
Lapatinib and Sulfamethoxazole can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Why it happens
Additive pharmacodynamic QT prolongation; the contribution of sulfamethoxazole is modest and not well established.
What to do
Obtain a baseline ECG and correct potassium and magnesium before combining. Repeat the ECG if other QT-prolonging drugs are used or symptoms occur.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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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 Lapatinib with Sulfamethoxazole?
MediHelp rates the interaction as moderate. Lapatinib and Sulfamethoxazole can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Both lapatinib and sulfamethoxazole (usually given with trimethoprim) have been associated with QT interval prolongation. Combined use may add to the risk of arrhythmia, particularly with electrolyte disturbance or heart disease.
How serious is the interaction between Lapatinib and Sulfamethoxazole?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Obtain a baseline ECG and correct potassium and magnesium before combining. Repeat the ECG if other QT-prolonging drugs are used or symptoms occur.
What other medicines interact with Lapatinib?
MediHelp also lists interactions of Lapatinib with, for example, Dofetilide, Ibutilide, Pimozide. The full list is on the Lapatinib page.
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