Toxic algae in some New Zealand freshwater ponds

Trials were conducted to test the ability of yohimbine, 4-aminopyridine and doxapram given by intravenous injection to antagonise xylazine sedation in red deer (Cervus elaphus). Yohimbine produced the best and most consistent result. The mean time taken for 34 animals to stand spontaneously after receiving yohimbine (0.2 to 0.25 mg/kg) was 2 minutes 25 seconds and this occurred, on average, 33 minutes after the initial doze of xylazine. Control deer took 67 and 104 minutes on average to stand after receiving intravenous (0.64–0.96 mg/kg) and intramuscular (1.0–1.5 mg/kg) injections of xylazine respectively. Two deer which received an overdose of xylazine (4 mg/kg) recovered 3 and 9 minutes respectively after receiving yohimbine. Two deer given a high intravenous dose of yohimbine (1.0 mg/kg) became mildly nervous and anxious, but returned to normal within an hour. 4-aminopyridine (0.3 mg/kg) alone produced some arousal from xylazine sedation (0.6–1.0 mg/kg) but was inconsistent. In combination with yohimbine (0.125 mg/kg) it produced rapid recovery in two deer but caused convulsions in two other deer.

Doxapram (1 mg/kg) produced respiratory stimulation and some arousal from xylazine sedation (0.6–1.0 mg/kg) in the majority of deer but the effect was transitory. Animals relapsed into moderate sedation and recumbency within 10 minutes and required vigorous stimulation to arouse them again.

Yohimbine, administered by intravenous injection at a dose rate of 0.2 to 0.25 mg/kg, appears to be a safe and reliable drug for the reversal of xylazine sedation in deer.