Acepromazine-xylazine combination in dogs: antagonism with 4-aminopyridine and yohimbine.

ABSTRACT

Groups of fasted atropinized crossbred dogs of both sexes were injected IM with a standard dosage of a xylazine-acepromazine combination (2.2 mg/kg and 0.5 mg/kg, respectively). Righting reflex was uniformly lost and considered to be the point of maximum sedation. After maximal sedation, dogs were injected IV with 4-amino-pyridine (4-AP, 0.5 mg/kg), yohimbine (0.25 mg/kg), or a combination of 4-AP and yohimbine. Controls were given (IV) 1 ml of saline solution. The 4-AP, yohimbine, and 4-AP + yohimbine significantly reduced walk times (time to arousal and ability to walk on a leash) from a control value of 43.1 minutes to 7.6, 4.4, and 1.9 minutes, respectively (P less than 0.05). Relapse to unconsciousness did not occur with any antagonist regimen and recovery was uneventful. In 3 dogs sedated with the xylazine-acepromazine combination supplemented with halothane having surgically placed cannulas and electrodes for measurement of electroencephalo-, electrocardio-, and electromyographic (EEG, ECG, and EMG) responses, arterial blood pressure, and respiratory rates and depth, IV injection of 4-AP + yohimbine caused transient femoral arterial hypotension with tachycardia, increases in respiratory rate, depth, and minute volume, increased EMG and EEG activities preceding and accompanying gross movements, slight speeding of ECG, and behavioral arousal within 3 minutes. Increased heart rate also was observed in intact dogs given yohimbine. Increased rate and depth of respiration also was seen in all intact dogs given antagonists. Curiously, the xylazine-acepromazine combination did not induce arterial hypotension as expected from the product literature. To what extent pretreatment with atropine sulfate may have counteracted this effect is unknown.(ABSTRACT TRUNCATED AT 250 WORDS)