Tetracyclines and niacinamide in canine dermatology (Proceedings)

Nov 01, 2010

The tetracyclines were initially used as bacteriostatic antibiotics. Niacinamide (the amide of niacin) is a vasodilator. These agents also have some interesting in vitro and in vivo anti-inflammatory and immunomodulatory properties:

      1. Decrease T-lymphocyte blastogenic response to mitogens.
      2. Decrease antibody production.
      3. Decrease complement activation.
      4. Decrease chemotactic responses of neutrophils.
      5. Decrease chemotactic responses of eosinophils.
      6. Decrease prostaglandin synthesis.
      7. Inhibit collagenase.
      8. Inhibit lipase.

      1. Decrease T-lymphocyte blastogenic responses to mitogens.
      2. Inhibit phosphodiesterase.
      3. Inhibit proteases.
      4. Prevent mast cell degranulation.
      5. Block antigen/IgE-induced histamine release.

The combination of tetracycline and niacinamide was initially used to treat certain canine autoimmune diseases: cutaneous (discoid) lupus erythematosus, pemphigus erythematosus, pemphigus foliaceus, and bullous pemphigoid. It was subsequently reported to be efficacious in some cases of lupoid onychitis, vasculitis, vesicular cutaneous lupus erythematosus (collies and shelties), exfoliative lupus erythematosus (German shorthair pointers), uveodermatologic syndrome (aka Vogt-Koyanagi-Harada syndrome), mucous membrane pemphigoid, various sterile granulomatous disorders (sterile granuloma-pyogranuloma syndrome; panniculitis; metatarsal fistulae), and cutaneous histiocytosis. Tetracycline and niacinamide can be used as a steroid-sparing agent. The combination is not effective for atopic dermatitis.

The traditional dosing of tetracycline and niacinamide is as follows: 250 mg of each, q8h, for a dog <10 kg; 500 mg of each, q8h, for a dog >10 kg. The combination is usually well-tolerated, with gastrointestinal side effects (vomiting, diarrhea, anorexia, lethargy) being the most common (and usually due to the niacinamide). These can be minimized by giving the agents with food, but not dairy products and mineral supplements. Some dogs may be maintained on twice or even once-a-day dosing. It appears that doxycycline (5 mg/kg q12h) can be substituted for tetracycline. Onset of clinical benefit is often slow and gradual, and 3 to 8 weeks of treatment is recommended before efficacy is assessed. Long-term treatment of dogs with tetracycline and niacinamide did not interfere with antibody responses to distemper and parvovirus vaccinations.

Remember: Niacinamide is not niacin. Large doses of niacin produce vasodilation, flushing, hypotension, tachycardia, and gastrointestinal side effects.


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