TREATMENT OF ACUTE ISONIAZID OVERDOSE IN DOGS

The National Animal Poison Control Center received 28 calls of isoniaz id (INH) exposures in dogs and cats between 1987 and 1993 The ingestio n of a single 300 mg INH tablet was the most common complaint. Isoniaz id has a low therapeutic margin and produces life threatening signs in dogs ingesting single 300 mg human tablets. The LD(50) of INH in dogs is estimated at 50 mg/kg bw, which is probably similar to that for hu mans. However, rodents are among the species most resistant to INH and thus are not good animal models for toxic dose extrapolation. The mor e consistent clinical signs reported were recurrent clonic-tonic seizu res followed by a stuporous state with poor response to stimulus. Idea l treatment combines vitamin B-6 given as a single iv bolus at an equi valent dose to the amount of INH ingested and anticonvulsants such as 1 mg diazepam/kg bw. This combination acts synergistically to improve GABAergic transmission in the CNS and has proved effective in protecti ng animals from further convulsions and death, even after several seiz ure episodes, as often encountered in clinical situations.