Behavioral and cardiorespiratory responses to 4-aminopyridine in healthy awake horses.

4-Aminopyridine was administered in incremental IV doses to healthy horses to evaluate cardiorespiratory and behavioral effects. Doses of 100 micrograms/kg produced apparent sensory discomfort, manifested by wiggling or curling of the lips and tongue, arching or stretching the neck, snorting, squealing, and coughing. At cumulative dosages of 300 to 500 micrograms/kg, muscle tremors, a stilted gait, and signs of excitement occurred. Once signs of excitement occurred, additional administration of 4-aminopyridine resulted in prolonged excitement consisting of severe muscle tremors and exaggerated responses to external stimuli. Heavy sedation with xylazine provided nearly complete relief from these effects. 4-Aminopyridine could be a useful adjunct to treatment of botulism in horses; however, administration of doses in excess of 300 to 500 micrograms/kg may cause severe CNS excitatory effects.