Clofazimine
Clofazimine is a highly lipophilic, phenazine dye antimycobacterial antibiotic. It is primarily utilized in veterinary medicine as part of a multi-drug regimen for treating leprosy-like syndromes (e.g., feline leprosy, canine leproid granuloma) and *Mycobacterium avium* complex (MAC) infections. **Clinical Pearls:** * **Combination Therapy:** Because mycobacteria are notoriously difficult to eradicate and prone to developing resistance, clofazimine is almost never used as a monotherapy. * **Lipophilicity:** Its extreme lipophilicity causes it to accumulate heavily in fat and the reticuloendothelial system (macrophages). * **Staining:** The drug's nature as a dye leads to its hallmark side effect: profound, long-lasting discoloration of the skin, eyes, and bodily fluids. * **Availability:** It can be very difficult for veterinarians to obtain and accurately dose for small animals, often requiring the assistance of a compounding pharmacist.
Mechanism: Clofazimine exerts a slowly bactericidal effect against susceptible mycobacteria (*M. leprae*, *M. tuberculosis*, *M. avium* complex, *M. bovis*, *M. chelonei*). * **DNA Binding:** It binds directly to mycobacterial DNA (preferentially at guanine base sequences) โ blocks template function โ **inhibits DNA replication and cell growth**. * **Intracellular Accumulation:** It is heavily taken up by macrophages, concentrating the drug exactly where intracellular mycobacteria reside. * **Immunomodulation:** Exhibits anti-inflammatory and immunosuppressive properties, likely by inhibiting T-lymphocyte activation and proliferation, though the exact mechanism remains poorly understood.
Dosing by species
- Avian mycobacteriosis ยท 6 mg/kg PO once daily ยท PO ยท q24h ยท Protocol 1: with rifampin 45 mg/kg and ethambutol 30 mg/kg.
- Avian mycobacteriosis (recommended regime for raptors) ยท 1.5 mg/kg PO q24h ยท PO ยท q24h ยท Protocol 2: with ethambutol 20 mg/kg, cycloserine 5 mg/kg, enrofloxacin 15 mg/kg q12h.
- Mycobacterium avium complex (MAC) as part of a multi-drug regimen ยท 4 mg/kg PO once daily ยท PO ยท q24h ยท Other drugs that may be used in combination include doxycycline, clarithromycin, and/or enrofloxacin.
- M. avium intracellularae complex infections, leprosy, or opportunistic mycobacteriosis ยท 4-8 mg/kg PO once a day ยท PO ยท q24h ยท 4 weeks ยท Usually as part of a multi-drug protocol.
- Mycobacterial infections ยท 4-8 mg/kg ยท PO ยท q24h ยท 2-6 months ยท Generally used in combination therapy with other antimicrobials including fluoroquinolones and clarithromycin.
- Treatment of feline leprosy ยท 25-50 mg once per day or 50 mg every other day ยท PO ยท q24h or q48h ยท Using a regimen of either two or three drugs (with clarithromycin and/or rifampin).
- Treatment of localized atypical mycobacterial infections ยท 8 mg/kg PO once daily ยท PO ยท q24h ยท At least 4 weeks beyond complete clinical resolution ยท Perform wide surgical excision of lesion if possible. Base antibiotic selection on culture and susceptibility results.
Routes of administration
Contraindications
- Use with caution in patients with pre-existing gastrointestinal conditions (diarrhea, abdominal pain)
- Known hypersensitivity to clofazimine
Adverse effects
- Skin, eye, and body fluid discoloration (pink to brownish-black)
- Gastrointestinal pain, nausea, vomiting, diarrhea (dose-limiting)
- Hepatotoxicity (reported in a dog receiving concurrent rifampin)
- Photosensitization (reported in a cat)
- Nausea
- Diarrhoea
- Discoloration of skin, eyes, and body fluids (red-brown/orange)
- Renal impairment
- Hepatic impairment
- Photosensitization
Drug interactions
- Isoniazid ยท May reduce clofazimine levels in the skin and increase amounts in plasma and urine; clinical significance is unclear.
- Dapsone ยท May reduce the anti-inflammatory effects of clofazimine; clinical significance is unclear.
Monitoring
- Efficacy against mycobacterial disease
- Adverse effects (primarily gastrointestinal)
- Hepatic function (especially in dogs)
- Hepatic function (ALT, AST, ALP, Bilirubin)
- Renal function (BUN, Creatinine, SDMA)
- Clinical signs of photosensitization
- Gastrointestinal tolerance
Overdose
Very limited data is available. The LD50 for rabbits is 3.3 g/kg and is greater than 5 g/kg in mice, rats, and guinea pigs. Treatment, if required, would include gut emptying and supportive care. Contact an animal poison control center for additional guidance.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.