Ofloxacin and Doxepin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Doxepin
Ofloxacin
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
An increased risk of cardiotoxicity (QT prolongation, torsades de pointes, cardiac arrest)
Interaction Deep Dive
Concomitant use of doxepin and QT prolonging agents may cause additive QT interval effects1. Concomitant use of tricyclic antidepressants, including doxepin, and class IA antiarrhythmics, including disopyramide, may increase the risk of cardiotoxicity due to similar cardiac effects of these drugs 23.
Why it happens (mechanism)
Additive cardiac toxicity; additive QT interval prolongation
Literature reports
1 report — tap to read
a) Concomitant use of tricyclic antidepressants, including doxepin, and class IA antiarrhythmics, including disopyramide, may increase the risk of cardiotoxicity due to similar cardiac effects of these drugs 23. In a placebo controlled study, imipramine 3.5 mg/kg was administered daily to seven patients with severe depression and titrated doses to obtain therapeutic plasma concentrations. Two patients displayed premature atrial depolarizations and premature ventricular depolarizations before therapy. On patient had 33 premature atrial depolarizations (PAD) and 30 premature ventricular depolarizations (PVD) per hour, which decreased to 0.4 PAC and zero PVC per hour on imipramine. The other patient had 12 PAD and 169 PVD per hour before treatment and 1.8 PAD and 28.1 PVD per hour on imipramine. The authors also cautioned that the incidence of cardiotoxicity may increase if tricyclic antidepressants are administered with Type I antiarrhythmics. It was also recommended that quiNIDine and procainamide not be used to treat the arrhythmias of a tricyclic overdose. The similarities between these agents may exacerbate the cardiotoxicity 2.
Common questions
Can I take Ofloxacin and Doxepin together?
An increased risk of cardiotoxicity (QT prolongation, torsades de pointes, cardiac arrest) Always confirm with your pharmacist or prescriber before making any change.
How serious is the Ofloxacin and Doxepin interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Ofloxacin or Doxepin need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (3)
- Product Information: SINEQUAN(R) oral capsules, oral solution, doxepin HCl oral capsules, oral solution. Pfizer Inc. (per FDA), New York, NY, 2025.
- Kantor SJ, Glassman AH, Bigger JT Jr. et al: The cardiac effects of therapeutic plasma concentrations of imipramine. Am J Psychiatry 1978; 135:534-538. PubMed
- Bigger JT, Giardina EG, Perel JM, et al: Cardiac antiarrhythmic effect of imipramine hydrochloride. N Engl J Med 1977; 296:206-208. DOI
Keep reading about Doxepin
Keep reading about Ofloxacin
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