Dapsone
4,4'-diaminodiphenyl sulfone
Also known as: Avlosulfone · Dapsoderm-X · Dopsan · Novasulfone · Servidapsone · Sulfona · DADPS · dapsonum · DDS · diaminodiphenylsulfone · NSC-6091 · diaphenylsulfone · disulone · sulfonyldianiline
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Alternative treatment for pemphigus | 1 mg/kg PO q8h; with sulfasalazine at 10-40 mg/kg q8h | PO | q8h | — | 🌎 NA |
| Post-vaccination alopecia/vasculitis resistant to prednisone therapy | 1 mg/kg PO q8h | PO | q8h | — | 🌎 NA |
| Treating mycobacteriosis | 1.1 mg/kg PO q6h until remission, then 0.3 mg/kg q8-12h after recovery | PO | q6h initially, then q8-12h | Until remission, then maintenance | 🌎 NA |
| Adjunctive therapy of vasculitis | 1 mg/kg PO q8h | PO | q8h | — | 🌎 NA |
| Adjunctive treatment of Brown Recluse spider (Loxosceles spp.) bite | 1 mg/kg PO three times daily for 10 days | PO | TID | 10 days | 🌎 NA |
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Alternative to clofazimine for treating feline leprosy | 1 mg/kg once daily PO | PO | q24h | — | 🌎 NA |
| Treating mycobacteriosis | 8 mg/kg PO once daily for 6 weeks | PO | q24h | 6 weeks | 🌎 NA |
| Aural chondritis | 1 mg/kg PO q24h | PO | q24h | — | 🌎 NA |
- Alternative to clofazimine for treating feline leprosy: Caution: High risk of serious side effects. Intensive monitoring required.
- Treating mycobacteriosis: Caution: High risk of serious side effects. Intensive monitoring required.
- Aural chondritis: Caution: High risk of serious side effects. Intensive monitoring required.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Alternative treatment for Pneumocystis carinii pneumonia | 3 mg/kg PO once daily (q24h) | PO | q24h | 56 days | 🌎 NA |
- Alternative treatment for Pneumocystis carinii pneumonia: From one case report of treatment of a foal.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Dapsone is a sulfone antimicrobial and anti-inflammatory agent. Historically known for treating human leprosy, its veterinary use is largely relegated to a second-line or adjunctive therapy for specific immune-mediated dermatoses (e.g., pemphigus, cutaneous vasculitis) and certain atypical infections (e.g., mycobacteriosis, Pneumocystis jiroveci).
Clinical Pearl: Due to a high risk of severe adverse effects—particularly hepatotoxicity and blood dyscrasias—dapsone is rarely a first-choice drug. It is considered relatively contraindicated in cats due to their high susceptibility to methemoglobinemia and hemolytic anemia.
Mechanism of action
Antimicrobial action: Acts as a competitive antagonist of para-aminobenzoic acid (PABA). It inhibits the enzyme dihydropteroate synthase (DHPS) → blocks the synthesis of dihydrofolic acid → disrupts nucleic acid synthesis in susceptible organisms (similar to sulfonamides).
Anti-inflammatory action: Dapsone exerts potent immunomodulatory effects. It inhibits the myeloperoxidase-H2O2-halide system → suppresses the neutrophil respiratory burst. It also decreases neutrophil chemotaxis, complement activation, antibody production, and lysosomal enzyme synthesis, making it useful for sterile, neutrophil-driven inflammatory conditions like vasculitis or Brown Recluse spider bites.
Safety & warnings
Contraindications
- Cats (relatively contraindicated due to high risk of neurotoxicity and hemolytic anemia)
- Hypersensitivity to dapsone or other sulfone drugs
- Patients with severe anemias or preexisting blood dyscrasias
- Preexisting hepatic dysfunction (use with extreme caution)
Adverse effects
- Hepatotoxicity
- Dose-dependent methemoglobinemia
- Hemolytic anemia
- Thrombocytopenia
- Neutropenias
- Gastrointestinal effects (nausea, vomiting)
- Neuropathies
- Cutaneous drug eruptions
- Photosensitivity
- Potential carcinogen
Precautions
- Feline Sensitivity: Cats are highly susceptible to dapsone-induced blood dyscrasias and hepatotoxicity. Use is generally not recommended.
- Pregnancy: FDA Category C. Animal studies have shown adverse effects on the fetus. Use with caution in pregnant animals.
- Nursing: Excreted into milk in concentrations equivalent to plasma; hemolytic reactions have been seen in human neonates. Consider switching to milk replacer if required in a nursing dam.
- Hepatic Disease: Use with caution in animals with preexisting hepatic dysfunction due to hepatotoxic potential.
Drug interactions
May decrease the renal excretion of active metabolites of dapsone.
May increase risk of hematologic reactions occurring with dapsone.
May decrease plasma dapsone concentrations (7-10 fold).
May increase plasma dapsone concentrations (and vice versa) and potentially increase each other's toxicity.
Monitoring
- CBC with platelets every 2-3 weeks during first 4 months of treatment, then every 3-4 months
- Liver function tests
- Clinical signs of adverse effects (GI upset, drug eruptions, neurotoxicity, jaundice, cyanosis)
- Clinical efficacy
Pharmacokinetics
Half-life
Absorption
Rapidly and completely absorbed after oral administration to dogs.
Distribution
In dogs, the monoacetyl metabolite is only about 60% bound to plasma proteins (compared to almost completely bound in humans).
Metabolism
Hepatic metabolism, primarily via acetylation.
Elimination
Primarily eliminated via the kidneys as conjugates and unidentified metabolites.
Overdose
Because of its toxicity potential, specific species differences in sensitivity, and pharmacokinetics, it is recommended to contact an animal poison control center in cases of dapsone overdoses.
- Clinical Signs: In humans, overdoses generally cause nausea, vomiting, and hyperexcitability within minutes. Methemoglobinemia with associated depression, seizures, and cyanosis can occur. Hemolysis may be delayed, occurring 7-14 days after the overdose.
- Treatment: Includes removal of drug from the gut (decontamination), methylene blue for methemoglobinemia, and sometimes hemodialysis to enhance removal of the drug and its monoacetyl metabolite.
Available products
Formulations
- Oral Tablets
- Compounded oral suspension
Human-labeled
- Dapsone Oral Tablets: 25 mg & 100 mg (scored)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store tablets protected from light at controlled room temperature (20-25°C, 68-77°F). Tablets may be compounded into a stable liquid dosage form (2 mg/mL) using a 1:1 ratio of Ora-Plus:Ora-Sweet; this preparation is stable for 90 days stored refrigerated or at room temperature.
Client information
- Strict Monitoring: This medication requires close veterinary supervision. Frequent blood tests are necessary to monitor your pet's liver and red blood cells.
- Watch for Toxicity: Contact your veterinarian immediately if you notice pale or bluish gums, yellowing of the eyes/skin (jaundice), extreme lethargy, rapid breathing, vomiting, or unusual weakness.
- Sun Protection: Dapsone can cause photosensitivity. Protect your pet's exposed skin from prolonged sunlight.
- Cats: If prescribed for a cat, understand that the risks of severe side effects are significantly higher.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.