Effects of yohimbine on combined xylazine-ketamine-induced sedation and immobilization in juvenile African elephants

Twenty-two juvenile African elephants were given a combination of xylazine (mean +/- SD = 0.14 +/- 0.03 mg/kg of body weight) and ketamine (1.14 +/- 0.21 mg/kg) as a single IM injection; one elephant was immobilized twice, 77 days apart. After injection, 14 elephants were immobilized, 4 were sedated deeply, 2 were sedated moderately, and 2 were sedated minimally. Immobilized elephants had a mean immobilization time of 11.6 +/- 6.9 minutes. At the conclusion of a variety of clinical procedures, 12 of the 14 elephants immobilized with a single dose combination of xylazine and ketamine were given yohimbine (0.13 +/- 0.03 mg/kg) IV, and the remaining 2 elephants were allowed to recover spontaneously; the elephants given yohimbine had a mean standing time of 2.4 +/- 1.1 minutes. Of the 8 sedated elephants, 5 were given an additional dose of combined xylazine (0.08 +/- 0.03 mg/kg), and ketamine (0.61 +/- 0.19 mg/kg) IM, and 1 elephant was given ketamine (0.47 mg/kg) IV. After injection, 4 of the 8 elephants were recumbent laterally within 17 minutes and 2 remained standing, under deep sedation. Seven of the 8 elephants were given yohimbine (0.13 +/- 0.03 mg/kg) IV; all were ambulatory in 2 minutes. Results indicated that yohimbine may be useful in controlling duration of xylazine-ketamine sedation and immobilization in juvenile African elephants.     

Comparison of yohimbine, 4-aminopyridine and doxapram antagonism of xylazine sedation in deer (Cervus elaphus)

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.     

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.     

Effects of tolazoline and yohimbine on xylazine-induced central nervous system depression, bradycardia, and tachypnea in sheep

We compared the ability of tolazoline and yohimbine to antagonize xylazine-induced central nervous system depression, bradycardia, and tachypnea in 9 ewes and 5 rams. Once a week for 3 weeks, each sheep received one IV treatment of 0.4 mg xylazine/kg, 0.4 mg xylazine/kg followed in 10 minutes by 2 mg tolazoline/kg, or 0.4 mg xylazine/kg followed in 10 minutes by 0.2 mg yohimbine/kg. The order of the 3 treatments in each sheep was randomized. Xylazine alone caused recumbency for 41.0 +/- 3.7 minutes (mean +/- SEM). Tolazoline and yohimbine shortened the xylazine-induced recumbency to 12.1 +/- 0.9 minutes and 18.1 +/- 1.5 minutes, respectively. Sheep given xylazine alone had head droop for 34.0 +/- 5.4 minutes after rising. Head drooping of sheep given tolazoline or yohimbine was reduced to 10.1 +/- 1.7 minutes and 14.2 +/- 1.7 minutes, respectively. Both tolazoline and yohimbine reversed the bradycardia and tachypnea that followed xylazine administration. No statistical differences in the rate and magnitude of the reversal were observed between the 2 drugs.     

Xylazine as an immobilizing agent for captive white-tailed deer.

Xylazine, at dosages of 0.89 to 8.00 mg/kg of body weight, was injected intramuscularly by manual or projectile syringe into 68 captive white-tailed deer (Odocoileus virginianus) to facilitate handling. Of 63 deer given the intended dose, 59 were moderately to deeply sedated and immobilized. Deer began to react visibly within 0.75 to 4.25 minutes after injection. Mean induction time (+/- SD) was 5.15 +/- 4.08 minutes and mean duration of immobilization was 197.90 +/- 101.13 minutes. Other than the prolongation of immobilization at dosages larger than or equal to 3 mg/kg, these times were not significantly affected by dosage or sex of the deer. Induction times were shorter in fawns than in older deer and much shorter in freshly trapped deer than in deer that had been trapped but kept undisturbed in semidarkened pens for 6 to 48 hours or in deer that were semitame captives. Dosages as low as 0.89 mg/kg were effective, and the safety margin appeared to be at least 8 times the minimal effective dose; however, immobilized deer were frequently unable to maintain sternal recumbency and required attention throughout the period of immobilization.     

Antagonistic effect of atipamezole on xylazine-induced sedation, bradycardia, and ruminal atony in calves.

Three doses of an alpha 2-adrenoreceptor antagonist, atipamezole, were administered to reverse xylazine-induced sedation, bradycardia, and ruminal atony in calves. Once a week for 4 weeks, each of 6 calves was administered IV 1 treatment of: 0.3 mg of xylazine/kg of body weight, followed in 10 minutes by 1 ml of 0.9% NaCl; 0.3 mg of xylazine/kg, followed in 10 minutes by 3 micrograms of atipamezole/kg; 0.3 mg of xylazine/kg, followed in 10 minutes by 10 micrograms of atipamezole/kg; or 0.3 mg of xylazine/kg, followed in 10 minutes by 30 micrograms of atipamezole/kg. The order of the 4 treatments in each calf was selected at random. Xylazine alone caused lateral recumbency for 33.6 +/- 7.1 minutes (mean +/- SEM). Atipamezole administered at dosages of 3, 10, and 30 micrograms/kg shortened xylazine-induced lateral recumbency to 20.5 +/- 3.0, 10.2 +/- 0.2, and 9.3 +/- 0.5 minutes, respectively. Calves given xylazine alone stood at greater than 60 minutes after the onset of recumbency. Atipamezole given at 3, 10, and 30 micrograms/kg shortened the time from onset of lateral recumbency to standing to 40.2 +/- 6.9, 12.8 +/- 1.1, and 10.0 +/- 0.7 minutes, respectively. Drowsiness was found in calves given the lowest dosage of atipamezole (3 micrograms/kg) after the calves stood. Atipamezole given at dosages of 10 and 30 micrograms/kg reversed xylazine-induced ruminal atony in a dose-dependent manner. In addition, 30 micrograms of atipamezole/kg reversed xylazine-induced bradycardia, but the lower dosages of this antagonist did not. Results indicated that 30 micrograms of atipamezole/kg should be a useful antidote for xylazine overdose in cattle.     

Antagonism of xylazine sedation with yohimbine, 4-aminopyridine, and doxapram in dogs

Groups of atropinized dogs (6 dogs/group) were sedated with xylazine (2.2 mg/kg of body weight, IM). At recumbency, the dogs were given IV saline solution (control groups), yohimbine (0.05, 0.1, and 0.2 mg/kg), 4-aminopyridine (4-AP; 0.3, 0.6, and 0.9 mg/kg), doxapram (0.5, 1.0, 2.0, and 4.0 mg/kg), or the smallest dose of these antagonists in dual combinations or in triple combination. Two additional groups were sedated with an overdose of xylazine (11 mg/kg, IM). At recumbency, 1 of these groups was given saline solution IV and the other group was given yohimbine IV (0.4 mg/kg) as the antagonist. With the 2.2 mg/kg dose of xylazine, control mean arousal time (MAT) and mean walk time (MWT) were 15.5 minutes and 24.8 minutes, respectively. These values were decreased by the individual antagonists to 0.5 to 2.5 minutes and 0.9 to 7.4 minutes, respectively. Approximate equipotent doses of antagonists (mg/kg) were: yohimbine, 0.2; 4-AP, 0.6; and doxapram, 0.5. Relapses did not occur after yohimbine or 4-AP. With doxapram, muscle tremors and spasms, abnormal postures, or aggressive behavior occurred in several dogs and several dogs had partial or complete relapses. The small doses of individual antagonists were synergistic with regard to MAT, MWT, and duration of residual sedation, but the various combinations of antagonists were not more effective in these regards than were larger doses of the single antagonists. With the overdose of xylazine, control MAT and MWT were 41.5 minutes and 144.5 minutes, respectively. Yohimbine decreased these values to 2.2 minutes and 2.5 minutes, respectively. Relapses did not occur.(ABSTRACT TRUNCATED AT 250 WORDS)     

Antagonistic effect of idazoxan on xylazine-induced central nervous system depression and bradycardia in calves

Two doses of an alpha 2-adrenoreceptor antagonist, idazoxan, were administered to reverse the CNS depressant and bradycardia effects of xylazine in calves. Once a week for 3 weeks, each of 6 calves were administered IV one treatment of: (1) 0.2 mg of xylazine/kg of body weight followed in 10 minutes by 1 ml of 0.9% NaCl, (2) 0.2 mg of xylazine/kg followed in 10 minutes by 10 micrograms of idazoxan/kg, or (3) 0.2 mg of xylazine/kg followed in 10 minutes by 30 micrograms of idazoxan/kg. The order of the 3 treatments in each calf was selected at random. Xylazine alone caused lateral recumbency for 27.2 +/- 3.0 minutes (mean +/- SEM). Idazoxan administered at dosages of 10 and 30 micrograms/kg shortened xylazine-induced lateral recumbency to 11.5 +/- 0.8 and 10.3 +/- 0.2 minutes, respectively. Calves given xylazine alone stood at greater than 60 minutes after the onset of recumbency. Idazoxan given at dosages of 10 and 30 micrograms/kg shortened the time to standing to 16.8 +/- 1.7 and 11.3 +/- 0.2 minutes, respectively. Idazoxan given at a dosage of 30 micrograms/kg also reversed xylazine-induced bradycardia. Results indicated that idazoxan should be a useful antidote for xylazine overdose in cattle.     

Antagonism of xylazine sedation in steers by doxapram and 4-aminopyridine

Five groups of 6 fasted crossbred steers were injected IM with standard dosages of xylazine hydrochloride (0.3 to 0.5 mg/kg). At maximal sedation, the steers were injected IV with the antagonists' doxapram (1.0 mg/kg), doxapram + yohimbine (0.125 mg of yohimbine/kg), doxapram + 4-aminopyridine (4-AP; 0.3 mg of 4-AP/kg), or 4-AP + yohimbine. One group was given 1.0 ml of saline solution IV instead of antagonists. Doxapram, doxapram + yohimbine, doxapram + 4-AP, and 4-AP + yohimbine decreased mean standing time (time from antagonist injection until animal could stand unaided) to 17.0, 4.3, 3.3, and 4.5 minutes, respectively--significantly (P less than 0.05) down from a control value of 49.8 minutes. Mean total recovery time (time from xylazine injection until animal resumed eating) was decreased to 78 minutes by doxapram and 81.6 minutes by doxapram + 4-AP--significantly (P less than 0.05) down from the control value of 142.9 minutes. Respiratory character was improved (depth of respiration was increased) only by doxapram + 4-AP. Relapses to recumbency and marked sedation were not seen in steers given doxapram + 4-AP or the saline solution. One steer given doxapram, 2 given doxapram + yohimbine, and 1 given 4-AP + yohimbine relapsed to recumbency and sedation. Recovery was relatively smooth in steers given doxapram + 4-AP or 4-AP + yohimbine. Animals given doxapram or doxapram + yohimbine had difficult recoveries.(ABSTRACT TRUNCATED AT 250 WORDS)     

Use of tolazoline as an antagonist to xylazine-ketamine-induced immobilization in African elephants

A group of 15 African elephants (Loxodonta africana) were immobilized with a combination of xylazine (0.2 mg/kg of body weight, IM) and ketamine (1 to 1.5 mg/kg of body weight, IM). Ten of the African elephants were allowed to remain recumbent for 30 minutes and the remaining 5 elephants, for 45 minutes before they were given tolazoline (0.5 mg/kg of body weight, IV). For the group of 15, the mean induction time (the time required from injection of the xylazine-ketamine combination until onset of recumbency) was 14.2 +/- 4.35 minutes (mean +/- SD), and standing time (the time required from the tolazoline injection until the elephant stood without stimulation or assistance) was 2.8 +/- 0.68 minutes. All of the elephants were physically stimulated (by pushing, slapping, shouting) before they were given tolazoline, and none could be aroused. After tolazoline was given and the elephant was aroused, relapses to recumbency did not occur. Recovery was characterized by mild somnolence in an otherwise alert and responsive animal. Failure (no arousal) rates were 0% (95% confidence interval, 0 to 0.3085) for elephants given tolazoline after 30 minutes of recumbency and 100% for elephants that were not given tolazoline. There was no significant (P less than 0.05) difference in standing time 30 or 45 minutes after tolazoline injection.     

Antagonism of xylazine sedation by 4-aminopyridine and yohimbine in cattle

Twenty-four crossbred steers (4 groups of 6 steers each) were injected IM with a standard dosage range of xylazine hydrochloride (0.2 to 0.3 mg/kg of body weight). When the steers were maximally sedated, group I (control group) were given isotonic saline solution (1 ml, IV), group II were given 4-aminopyridine (4-AP, 0.3 mg/kg) IV, group III were given yohimbine hydrochloride (0.125 mg/kg) IV, and group IV were given 4-AP (0.3 mg/kg) plus yohimbine hydrochloride (0.125 mg/kg) IV. The 4-AP decreased mean standing time (MST; time until animal could stand unaided) from 94.3 minutes (control) to 13.4 minutes. Yohimbine decreased MST to 27 minutes. The combination of 4-AP + yohimbine decreased MST to 7.4 minutes. Mean total recovery time (MTRT; time from xylazine injection until normal behavior, including eating and drinking) was not significantly (P = greater than 0.05) decreased from control values by any of the antagonists tested. The combination of 4-AP + yohimbine decreased MST in animals given a 3X overdose of xylazine (0.6 mg/kg) from 124 minutes (control) to 30.3 min. The MTRT was not significantly (P greater than 0.05) decreased from control values. Two animals given a 5X overdose of xylazine (1 mg/kg) and then given 4-AP + yohimbine had a MST of 32.5 minutes and a MTRT of 3.7 hours. The combination of 4-AP + yohimbine produced marked antagonism of xylazine sedation in cattle. The combination of antagonists may prove to be useful for the arousal of animals sedated with xylazine alone or with a combination of sedatives including xylazine.     

Effects of idazoxan, tolazoline, and yohimbine on xylazine-induced respiratory changes and central nervous system depression in ewes

We compared the ability of 3 alpha 2-adrenoreceptor antagonists, idazoxan (0.05 mg/kg), tolazoline (2 mg/kg), and yohimbine (0.2 mg/kg) to reverse xylazine (0.3 mg/kg)-induced respiratory changes and CNS depression in 6 ewes. Once weekly, each ewe was given a random IV treatment of xylazine, followed in 5 minutes by either an antagonist or 0.9% NaCl solution. Xylazine alone caused recumbency for 54.2 +/- 5.3 minutes (mean +/- SEM). Xylazine also increased respiratory rate and decreased PaCO2 for at least 45 minutes, but did not significantly change arterial pH or PaCO2. Idazoxan and tolazoline were equally effective in reversing the respiratory actions of xylazine; however, yohimbine was less effective in reducing the respiratory rate and was ineffective in antagonizing the decreased PaO2. Idazoxan and tolazoline decreased the duration of xylazine-induced recumbency to 6.3 +/- 0.6 and 9.5 +/- 2.3 minutes, respectively, whereas yohimbine did not significantly change this effect of xylazine. Thus, at the dosages studied, idazoxan and tolazoline appeared to be more effective than yohimbine in reversing the respiratory and CNS depressant actions of xylazine in sheep.     

Clinical evaluation of intranasal benzodiazepines, alpha-agonists and their antagonists in canaries

OBJECTIVE: To evaluate the effects of intranasal benzodiazepines (midazolam and diazepam), alpha(2)-agonists (xylazine and detomidine) and their antagonists (flumazenil and yohimbine) in canaries. STUDY DESIGN: Prospective randomized study. ANIMALS: Twenty-six healthy adult domesticated canaries of both sexes, weighing 18.3 +/- 1.0 g. METHODS: In Study 1 an attempt was made to determine the dose of each drug that allowed treated canaries to be laid in dorsal recumbency for at least 5 minutes, i.e. its effective dose. This involved the evaluation of various doses, during which equal volumes of the tested drug were administered slowly into each nostril. In study 2 the onset of action, duration and quality of sedation induced by each drug at its effective dose were evaluated. The efficacy of flumazenil and yohimbine in antagonizing the effects of the sedative drugs was also studied. RESULTS: In study 1 administration of 25 microL per nostril diazepam (5 mg mL(-1) solution) or midazolam (5 mg mL(-1) solution) to each bird caused adequate sedation within 1-2 minutes; birds did not move when placed in dorsal recumbency. After administration of 12 microL per nostril of either xylazine (20 mg mL(-1)) or detomidine (10 mg mL(-1)), birds seemed heavily sedated and assumed sternal recumbency but could not be placed in dorsal recumbency. Higher doses of xylazine (0.5 mg per nostril) or detomidine (0.25 mg per nostril) prolonged sedation but did not produce dorsal recumbency. In study 2 in all treatment groups, onset of action was rapid. Duration of dorsal recumbency was significantly longer (p < 0.05) with diazepam (38.4 +/- 10.5 minutes) than midazolam (17.1 +/- 2.2 minutes). Intranasal flumazenil (2.5 microg per nostril) significantly reduced recumbency time. Duration of sedation was longer with alpha(2)-agonists compared with benzodiazepines. Detomidine had the longest duration of effect (257.5 +/- 1.5 minutes) and midazolam the shortest (36.9 +/- 2.4 minutes). Nasally administered flumazenil significantly reduced the duration of sedation with diazepam and midazolam while yohimbine (120 microg per nostril) effectively antagonized the effects of xylazine and detomidine. CONCLUSION: Intranasal benzodiazepines produce rapid and effective sedation in canaries. Intranasal alpha(2) agonists produce sedation but not sustained recumbency. Specific antagonists are also effective when used by this route. Clinical relevance Intranasal sedative drug administration is an acceptable alternative method of drug delivery in canaries.     

Antagonism of xylazine-pentobarbital anesthesia by yohimbine in ponies

Effects of yohimbine on xylazine-pentobarbital anesthesia were evaluated in ponies. Five minutes after the IV injection of xylazine (1.1 mg/kg of body weight), pentobarbital sodium (12.7 mg/kg, IV) and additional xylazine (2.2 mg/kg, IM) were given and produced anesthesia in 12 ponies for 64.0 +/- 16.4 minutes (mean +/- SD) as well as immobilization for 89.8 +/- 34.2 minutes. Eleven ponies were given yohimbine (0.1 mg/kg, IV) 50 minutes after pentobarbital dosing. In these 11 ponies, durations of anesthesia and immobilization were shorter, 52.0 +/- 1.4 and 65.5 +/- 14.8 minutes, respectively. The xylazine-pentobarbital combination caused bradycardia that was reversed by yohimbine injection. Xylazine-pentobarbital produced a small, but steady, decrease of mean arterial blood pressure, which was compounded by yohimbine administration and was evident for approximately 2 minutes. Within a minute after yohimbine injection, the ponies' respiratory rate decreased and the length of inspiration and expiration and thoracic breathing increased. This lasted approximately 2 to 3 minutes and was followed by an increase in respiratory rate. The anesthesia also produced a decrease in PaO2 that gradually returned to base line in 12 control ponies, but was more pronounced in 11 ponies given yohimbine. The PaCO2, although remaining moderately high in control ponies, returned to base line after yohimbine injection. An increased pHa was seen 60 minutes after induction of anesthesia and was especially noticeable after yohimbine administration. Decreases in the number of WBC, hemoglobin content, PCV, plasma protein and serum aspartate transaminase resulting from xylazine-pentobarbital were reversed by yohimbine. Conversely, serum glucose values and creatine kinase activities were increased by xylazine-pentobarbital.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sedative effects of midazolam and xylazine with or without ketamine and detomidine alone following intranasal administration in Ring-necked Parakeets

OBJECTIVE: To evaluate the effects of intranasal administration of midazolam and xylazine (with or without ketamine) and detomidine and their specific antagonists in parakeets. DESIGN: Prospective study. ANIMALS: 17 healthy adult Ring-necked Parakeets (Psittacula krameri) of both sexes (mean weight, 128.83+/-10.46 g [0.28+/-0.02 lb]). PROCEDURE: The dose of each drug or ketamine-drug combination administered intranasally that resulted in adequate sedation (ie, unrestrained dorsal recumbency maintained for >or=5 minutes) was determined; the onset of action, duration of dorsal recumbency, and duration of sedation associated with these treatments were evaluated. The efficacy of the reversal agents flumazenil, yohimbine, and atipamezole was also evaluated. RESULTS: In parakeets, intranasal administration of midazolam (7.3 mg/kg [3.32 mg/lb]) or detomidine (12 mg/kg [5.45 mg/lb]) caused adequate sedation within 2.7 and 3.5 minutes, respectively. Combinations of midazolam (3.65 mg/kg [1.66 mg/lb]) and xylazine (10 mg/kg [4.55 mg/lb]) with ketamine (40 to 50 mg/kg [18.2 to 22.7 mg/lb]) also achieved adequate sedation. Compared with detomidine, duration of dorsal recumbency was significantly longer with midazolam. Intranasal administration of flumazenil (0.13 mg/kg [0.06 mg/lb]) significantly decreased midazolam-associated recumbency time. Compared with the xylazineketamine combination, duration of dorsal recumbency was longer after midazolam-ketamine administration. Intranasal administration of flumazenil, yohimbine, or atipamezole significantly decreased the duration of sedation induced by midazolam, xylazine, or detomidine, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Intranasal administration of sedative drugs appears to be an acceptable method of drug delivery in Ring-necked Parakeets. Reversal agents are also effective when administered via this route.     

Effect of tolazoline on xylazine-ketamine-induced anesthesia in turkey vultures

Fifteen turkey vultures were each given xylazine (1 mg/kg of body weight, IM) and ketamine (10 mg/kg, IM). In 5 of the birds (controls), the mean (+/- SD) induction time was 5.4 +/- 1.0 minutes and the mean duration of anesthesia was 109.8 +/- 25.4 minutes. The remaining 10 vultures (test birds) were given tolazoline (15 mg/kg, IV) 45 minutes after administration of xylazine and ketamine. In the test birds, the mean induction time was 4.5 +/- 1.6 minutes and the mean duration of anesthesia was 49 +/- 2.1 minutes. After administration of tolazoline, the birds regained consciousness in 3.7 +/- 1.9 minutes and were standing with normal posture in 14.2 +/- 5.4 minutes. All birds remained moderately sedated yet ambulatory and responsive to stimuli for 30 to 60 minutes after tolazoline administration. Results indicated that tolazoline was useful in controlling the duration of xylazine-ketamine-induced anesthesia in turkey vultures.     

Preliminary study of the effects of xylazine or detomidine with or without butorphanol for standing sedation in dairy cattle

The sedative effect induced by administering xylazine hydrochloride or detomidine hydrochloride with or without butorphanol tartrate to standing dairy cattle was compared in two groups of six adult, healthy Holstein cows. One group received xylazine (0.02 mg/kg i.v.) followed by xylazine (0.02 mg/kg) and butorphanol (0.05 mg/kg i.v.) 1 week later. Cows in Group B received detomidine (0.01 mg/kg i.v.) followed by detomidine (0.01 mg/kg i.v.) and butorphanol (0.05 mg/kg i.v.) 1 week later. Heart rate, respiratory rate, and arterial blood pressure were monitored and recorded before drugs were administered and every 10 minutes for 1 hour after drug administration. The degree of sedation was evaluated and graded. Cows in each treatment group had significant decreases in heart rate and respiratory rate after test drugs were given. Durations of sedation were 49.0 +/- 12.7 minutes (xylazine), 36.0 +/- 14.1 (xylazine with butorphanol), 47.0 +/- 8.1 minutes (detomidine), and 43.0 +/- 14.0 minutes (detomidine with butorphanol). Ptosis and salivation were observed in cows of all groups following drug administration. Slow horizontal nystagmus was observed from three cows following administration of detomidine and butorphanol. All cows remained standing while sedated. The degree of sedation seemed to be most profound in cows receiving detomidine and least profound in cows receiving xylazine.     

Xylazine and a xylazine/fentanyl citrate/azaperone combination in farmed deer. II: velvet antler removal and reversal combinations

Three studies were undertaken on farmed red and red x wapiti deer to evaluate xylazine and a xylazine/fentanyl citrate/azaperone combination for velvet antler removal. In the first experiment, 30 1-2 year-old red and 25% red x wapiti deer whose velvet was to be removed were given either 5% xylazine alone at 0.5 mg/kg body weight intramuscularly or the same dose rate of a commercially available mixture of 5% xylazine with the addition of 0.4 mg of fentanyl citrate and 3.2 mg of azaperone per ml. Physiological, behavioural and analgesic responses and reversal times after yohimbine or yohimbine and naloxone were monitored. There were no differences in heart rate, respiration rate, sedative or analgesic properties detected between xylazine or the xylazine/fentanyl citrate/azaperone combination. All deer became recumbent, but those given the xylazine/fentanyl citrate/azaperone combination became recumbent more rapidly than those given xylazine alone (9.4 and 12.5 minutes, respectively, p<0.05). The arousal pattern and timing of reversal of xylazine and xylazine/fentanyl citrate/azaperone using yohimbine and yohimbine and naloxone, respectively, were similar. The second experiment evaluated the reversal of the xylazine/fentanyl citrate/azaperone combination with either yohimbine or yohimbine and naloxone in 43 3-year-old red deer stags after velvet antler removal. There were no differences in arousal pattern or time to standing between reversal treatments. Sixteen 1-year-old red and 25% red x wapiti stags were used in the third experiment to evaluate clinically the analgesic properties of xylazine and xylazine/fentanyl citrate/azaperone combination during velvet removal without the application of a local anaesthetic agent. Withdrawal responses were observed in most deer after the xylazine/fentanyl citrate/azaperone combination at dosages containing 0.5, 0.7 and 0.75 mg of xylazine/kg and after xylazine alone at 0.7 mg/kg, indicating that insufficient analgesia was provided by the systemic agent for the surgical procedure of velvet antler removal. These studies have shown that the knock-down effect of the xylazine/fentanyl citrate/azaperone combination was more rapid than that of xylazine alone, but that other physiological, behavioural and analgesic responses at doses used and evaluated by the methods used were similar. Reversal of both the xylazine and xylazine/fentanyl citrate/azaperone combination was similar when using either yohimbine alone for xylazine and the xylazine/fentanyl citrate/azaperone combination or yohimbine and naloxone for the xylazine/fentanyl citrate/azaperone combination. The evaluation of surgical analgesia for antler removal suggested that both xylazine alone and the xylazine/fentanyl citrate/azaperone combination provided insufficient analgesia and that local anaesthetic should be used in all cases.     

Use of yohimbine and 4-aminopyridine to antagonize xylazine-induced immobilization in North American Cervidae

Four captive moose (Alces alces), 4 mule deer (Odocoileus hemionus), and 5 white-tailed deer (Odocoileus virginianus) were immobilized with xylazine (0.63 to 1.29 mg/kg of body weight, IM). Mean induction times for the moose were 17 minutes and for the deer, 14 and 10 minutes, respectively. According to published data and past experience, the dosage of xylazine used would be expected to provide 115, 120, and 100 minutes of immobilization in captive moose, mule deer, and white-tailed deer, respectively. In the present study, maximal sedation of the moose and deer was reversed with successive injections (given IV) of yohimbine (0.15 mg/kg) and 4-aminopyridine (0.26 to 0.29 mg/kg). These produced sternal recumbency-to-arousal intervals of 1 to 15 minutes and recumbency-to-standing or walking intervals of 1 to 24 minutes. Relapses to recumbency were not observed. The injections of the reversal drugs produced marked increases in respiratory rate and heart in the moose and deer, without occurrence of muscle tremors or convulsions. The administrations of yohimbine and 4-aminopyridine markedly enhanced the speed of recovery from xylazine-induced immobilization in moose and deer.     

Sedation of the Asian elephant (Elephas maximus) with xylazine

Doses of 100 to 300 mg of a 10 per cent solution of xylazine satisfactorily sedated six elephants ranging from 150 to 255 cm shoulder height. At these dosages all animals were sedated in the standing position. The time taken to produce the initial signs of sedation ranged from 10 +/- 4 to 20 +/- 4 minutes and the effects lasted from 60 +/- 8 to 100 +/- 15 minutes. The time taken from injection to complete recovery ranged from 360 +/- 31 to 540 +/- 21 minutes. Recovery was uncomplicated. Repeated administration of as much as seven injections per animal at intervals of three to four days had no adverse effects. Disturbances during induction delayed the onset of action of the drug.