Vetgirl Veterinary Continuing Education Podcasts

In today's VETgirl online veterinary CE podcast, Dr. Justine Lee, DACVECC, DABT discusses isoniazid toxicosis in dogs. While isoniazid isn’t a common toxicant seen in dogs, this antimicrobial potentially be fatal when dogs get into poisonous amounts. Isoniazid (commonly known as INH) is a human medication used for tuberculosis. While it is used in veterinary medicine to treat Mycobacterium or Actinomyces, it has a narrow margin of safety in dogs and cats.1,2 This drug works by blocking the synthesis of mycolic acid. INH depletes the central nervous system (CNS) of pyridoxine and also decreases levels of GABA within the brain. Many assume that since this is an “antibiotic” that it is safe; however, when accidentally ingested in dogs (and rarely, cats), it can result in severe CNS signs (e.g., tremors, refractory seizures, coma, death). The LD50 in dogs is estimated to be as low as 50 mg/kg;1,2 at this same dose, seizures can be seen. One 300 mg tablet can result in severe poisoning in a 10-pound dog. Other cli