Drug interactions
Levofloxacin + Sulfamethoxazole
Severity: Moderate
Levofloxacin 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
Levofloxacin can prolong the QT interval, and sulfamethoxazole (usually given with trimethoprim) has been rarely linked to QT prolongation and arrhythmia. Combined use may add to the risk of torsades de pointes, particularly with electrolyte disturbances or underlying heart disease.
What this interaction means in plain words
Levofloxacin 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
Possible additive QT prolongation through cardiac potassium channel blockade; the contribution of sulfamethoxazole is weakly established.
What to do
Obtain a baseline ECG in patients with cardiac risk factors and correct potassium and magnesium before starting. Consider an alternative antibiotic if the patient has known QT prolongation or takes other QT-prolonging drugs.
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 Levofloxacin
- Dronedarone + Levofloxacin Contraindicated
- Ibutilide + Levofloxacin Contraindicated
- Levofloxacin + Thioridazine Contraindicated
- Levofloxacin + Vandetanib Contraindicated
- Levofloxacin + Ziprasidone Contraindicated
- Adagrasib + Levofloxacin Major
Frequently asked questions
Can I take Levofloxacin with Sulfamethoxazole?
MediHelp rates the interaction as moderate. Levofloxacin 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. Levofloxacin can prolong the QT interval, and sulfamethoxazole (usually given with trimethoprim) has been rarely linked to QT prolongation and arrhythmia. Combined use may add to the risk of torsades de pointes, particularly with electrolyte disturbances or underlying heart disease.
How serious is the interaction between Levofloxacin 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 in patients with cardiac risk factors and correct potassium and magnesium before starting. Consider an alternative antibiotic if the patient has known QT prolongation or takes other QT-prolonging drugs.
What other medicines interact with Levofloxacin?
MediHelp also lists interactions of Levofloxacin with, for example, Dronedarone, Ibutilide, Thioridazine. The full list is on the Levofloxacin page.
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