Dapsone and Trimethoprim: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Dapsone
Trimethoprim
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 dapsone toxicity (hemolytic anemia, methemoglobinemia, peripheral neuropathy) or trimethoprim toxicity (bone marrow depression, thrombocytopenia, leukopenia, megaloblastic anemia)
Interaction Deep Dive
In a randomized double-blind study, the concurrent use of trimethoprim and dapsone in patients with HIV with Pneumocystis infection resulted in an increase in plasma concentration of both drugs by approximately 40%1. However, a later study found no significant interaction between dapsone and trimethoprim in asymptomatic HIV-positive patients 2. Patients with HIV and acute illness may be more susceptible to this drug interaction. Further studies are necessary to delineate the clinical implications of this drug interaction in both groups of patients.
Why it happens (mechanism)
Altered clearance
Literature reports
2 reports — tap to read
a) Trimethoprim increased dapsone levels by 40% in patients with HIV. In addition, trimethoprim levels were 48.4% higher in patients receiving trimethoprim and dapsone than patients receiving trimethoprim and sulfamethoxazole. The patients taking trimethoprim and dapsone had a decreased rate of therapeutic failure and an increased rate of toxicity when compared to the group that took dapsone alone. It was theorized that the trimethoprim decreased the metabolism and excretion of dapsone. The mechanism by which dapsone increased trimethoprim levels is unknown. Possibly, it was due to competitive inhibition for excretion pathways between dapsone or monoacetyldapsone and trimethoprim 1.
b) In a controlled study of eight HIV-positive patients, the pharmacokinetic interactions between zidovudine, trimethoprim, and dapsone were assessed in two and three drug combinations. Patients received zidovudine 200 mg, trimethoprim 200 mg, or dapsone 100 mg alone and with one or two of the other agents. In contrast to results from previous studies, no significant changes in dapsone or trimethoprim pharmacokinetics were observed. In this study, the number of subjects may have been inadequate to detect any interactions and the subjects were asymptomatic HIV-positive patients whereas the previous study examined patients with HIV being treated for Pneumocystis pneumonia. The authors concluded that in most cases, zidovudine, trimethoprim, and dapsone can be given concurrently without a clinically significant interaction 2.
Common questions
Can I take Dapsone and Trimethoprim together?
An increased risk of dapsone toxicity (hemolytic anemia, methemoglobinemia, peripheral neuropathy) or trimethoprim toxicity (bone marrow depression, thrombocytopenia, leukopenia, megaloblastic anemia) Always confirm with your pharmacist or prescriber before making any change.
How serious is the Dapsone and Trimethoprim interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Dapsone or Trimethoprim 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 anything you'd monitor while I'm on both?
References (2)
- Lee BL, Medina I, Benowitz NL, et al: Dapsone, trimethoprim, and sulfamethoxazole plasma levels during treatment of pneumocystis pneumonia in patients with the acquired immunodeficiency syndrome (AIDS): evidence of drug interactions. Ann Intern Med 1989; 110:606-611. PubMed
- Lee BL, Safrin S, Makrides V, et al: Zidovudine, trimethoprim and dapsone pharmacokinetic interactions in patients with human immunodeficiency virus infection. Antimicrob Agents Chemother 1996; 40:1231-1236. DOI
Keep reading about Dapsone
Keep reading about Trimethoprim
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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