The subacute neurotoxicity of excess pyridoxine HCl and clioquinol (5-chloro-7-iodo-8-hydroxyquinoline) in beagle dogs. I. Clinical disease.

The clinical and clinicopathologic effects of excess oral pyridoxine hydrochloride (150 mg/kg body weight/day) and clioquinol (200 mg/kg body weight/day) alone and in combination were evaluated in adult Beagle dogs over an experimental period of approximately 100 days. Anorexia and loss of body weight occurred in the first weeks of the trial period in each treatment group, but was most severe in dogs given both compounds. Dogs in each treatment group (10 of 10 pyridoxine-treated dogs, 6 of 13 clioquinol-treated dogs and 12 of 13 pyridoxine plus clioquinol-treated dogs) developed neurologic disease, manifested principally by ataxia. Pyridoxine-treated dogs had proprioceptive loss involving both fore- and hindquarters, characterized by stiff, spastic, dysmetric leg movements. In clioquinol-treated dogs, dysmetric leg movements were accompanied by failure to support body weight in the hindquarters, but similar forelimb involvement occurred in severely affected dogs. The neurologic disease in dogs given both compounds varied; signs in some dogs resembled those of affected dogs of the pyridoxine-treated group, and in others, those in clioquinol-treated group. Erythrocyte counts, hemoglobin concentrations and packed cell volumes were reduced in dogs in each treatment group and were lowest in dogs given both compounds. Plasma protein was mildly reduced in dogs given pyridoxine or pyridoxine plus clioquinol. Few or no differences were present in the leukocyte counts, blood urea nitrogen concentrations, in activities of serum alanine aminotransferase and aspartate aminotransferase, and in concentrations of sodium, chloride or potassium in treated dogs as compared to control dogs.