Effect of yohimbine on xylazine-induced immobilization in white-tailed deer

Two groups of white-tailed deer were given IM injections of xylazine with a projectile syringe. Deer in one of the groups served as controls and did not receive any treatments other than xylazine. Deer in the other group were given yohimbine IV at various times (15 to 171 minutes) to evaluate its effect on xylazine-induced immobilization. In 5 control deer given 3.7 +/- 1.2 mg of xylazine/kg (mean +/- SD), onset of recumbency was 13 +/- 2 minutes and time to standing was 268 +/- 76 minutes. In 20 principal deer given 2.8 +/- 1.0 mg of xylazine/kg, onset of recumbency was 8 +/- 7 minutes, time to sitting after giving yohimbine was 3 +/- 4 minutes in 18 of the deer, and time to standing after giving yohimbine was 4 +/- 5 minutes in 19 of the deer. Most of these deer were still moderately sedated 30 minutes after injection of yohimbine, but none of them became reimmobilized or as deeply sedated as before the injection of yohimbine. Yohimbine also reversed the bradycardia and respiratory depression induced by xylazine.     

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.     

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)     

Evaluation of Three Midazolam-Xylazine Mixtures Preliminary Trials in Dogs

The depressant effects of midazolam and xylazine on the central nervous system (CNS) were evaluated in 12 dogs. Xylazine was administered to six dogs (1.1 mg/kg intravenously [IV]) followed in 5 minutes by midazolam (1.0 mg/kg intramuscularly [IM]). In a second group of six dogs, xylazine (2.2 mg/kg IM) was followed in 5 minutes by midazolam (1.0 mg/kg IV). Both drug regimens induced rapid and profound sedation or anesthesia. Duration of action varied with the doses and routes of administration. Dogs given the high dose of xylazine IM had an arousal time of 95.4 +/- 8.9 minutes and a walking time of 155.4 +/- 8.8 minutes. These values exceeded the IV xylazine values threefold. Partial reversal of CNS depression was accomplished with either a benzodiazepine antagonist (flumazenil) or an alpha-2 antagonist (yohimbine). In a separate trial, a mixture of xylazine (0.55 mg/kg), midazolam (1.0 mg/kg), and butorphanol (0.1 mg/kg) with and without glycopyrrolate was evaluated in eight dogs. As with the xylazine-midazolam combinations, the CNS depressant effect of this mixture was clinically indistinguishable from anesthesia achieved with other rapid-acting injectable agents. Clinical signs of CNS depression were readily and completely antagonized by the simultaneous injection of flumazenil and yohimbine.     

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.     

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)     

Sloth bear immobilization with a ketamine-xylazine combination: reversal with yohimbine

Five captive sloth bears (Melursus ursinus) were immobilized with a combination of ketamine (5.80 to 9.75 mg/kg of body weight) and xylazine (1.40 to 2.44 mg/kg), given IM. The youngest bear was immobilized twice, 62 days apart; all other bears were immobilized only once. Induction times were 4 to 25 minutes. After completion of various intended procedures, yohimbine (0.125 mg/kg) was administered IV. Arousal times were 2 to 20 minutes and bears were standing in 17 to 51 minutes. Compared with reported recovery times of 2 to 3 hours for bears immobilized with ketamine-xylazine combinations but not given an antagonist, results of the present study indicated that yohimbine reduces anesthesia recovery times in sloth bears immobilized with ketamine-xylazine combination.     

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 halothane to maintain anesthesia induced with etorphine in juvenile African elephants

Sixteen 3- to 5-year-old African elephants were anesthetized one or more times for a total of 27 diagnostic and surgical procedures. Xylazine (0.1 +/- 0.04 mg/kg of body weight, mean +/- SD) and ketamine (0.6 +/- 0.13 mg/kg) administered IM induced good chemical restraint in standing juvenile elephants during a 45-minute transport period before administration of general anesthesia. After IM or IV administration of etorphine (1.9 +/- 0.56 micrograms/kg), the mean time to lateral recumbency was 20 +/- 6.6 and 3 +/- 0.0 minutes, respectively. The mean heart rate, systolic blood pressure, and respiration rate during all procedures was 50 +/- 12 beats/min, 106 +/- 19 mm of Hg, and 10 +/- 3 breaths/min, respectively. Cardiac arrhythmias were detected during 2 procedures. One elephant with hypotension responded to a decrease in the concentration of halothane and IV infusion of dobutamine HCl. Alterations in systolic blood pressure, ear flapping, and trunk muscle tone were useful for monitoring depth of anesthesia. Results indicated that halothane in oxygen was effective for maintenance of surgical anesthesia in juvenile African elephants after induction with etorphine.     

Xylazine-ketamine-induced anesthesia in rats and its antagonism by yohimbine

A combination of xylazine and ketamine was used to anesthetize 60 male rats, and then yohimbine was given to evaluate its reversing effect on xylazine-ketamine-induced anesthesia. In experiment A, xylazine (21 mg/kg of body weight) and ketamine (45 mg/kg) were admixed and administered IM to 12 Sprague-Dawley rats. Anesthesia lasted approximately 70 minutes. The xylazine-ketamine combination also induced polyuria, bradycardia, and bradypnea. When yohimbine (2.1 mg/kg) was given intraperitoneally 20 minutes after the xylazine-ketamine injection, the rats regained consciousness and righting reflexes within approximately 10 minutes. Yohimbine also reversed the bradycardia and bradypnea and appeared to reduce the polyuria induced by the xylazine-ketamine combination. In experiment B, xylazine (15.4 mg/kg) and ketamine (33 mg/kg) were admixed and given IM to 48 Holtzman rats. The combination induced surgical anesthesia for at least 30 minutes, during which a surgical procedure involving grafting a section of the sciatic nerve into the hypothalamus was performed. In rats in which yohimbine (1 mg/kg) was given intraperitoneally 45 to 60 minutes after xylazine-ketamine administration (before natural recovery from the anesthesia), the righting reflex was apparent in less than 10 minutes.     

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.     

Anesthesia in the Richardson's ground squirrel: comparison of ketamine, ketamine and xylazine, droperidol and fentanyl, and sodium pentobarbital

A combination of ketamine and xylazine (88.9 mg of ketamine/ml and 11.1 mg of xylazine/ml) given IM (85.5 +/- 3.4 mg of ketamine/kg of body weight and 10.6 +/- 0.5 mg of xylazine/kg) or subcutaneously (85.6 +/- 4.0 mg of ketamine/kg and 10.7 +/- 0.7 mg of xylazine/kg) induced effective surgical anesthesia for 20 to 30 minutes in Richardson's ground squirrels. Use of ketamine alone (86 +/- 7 mg/kg, IM), a droperidol and fentanyl combination (2.6 +/- 0.4 mg of droperidol/kg and 52 +/- 8 micrograms of fentanyl/kg, IM), or sodium pentobarbital (50 +/- 2 mg/kg, intraperitoneally) did not induce surgical anesthesia, but did induce depressed respiratory rates in the squirrels.     

Serum concentrations of etorphine in juvenile African elephants

Eleven juvenile African elephants were given etorphine hydrochloride (2.19 +/- 0.11 micrograms/kg of body weight; mean +/- SD) as a single IM injection; 3 elephants were given additional etorphine (0.42 +/- 0.09 micrograms/kg) IV. After immobilization, each elephant was maintained in lateral recumbency by administration of a 0.5% halothane/oxygen mixture or by administration of multiple IV injections of etorphine. At postinjection hours 0.25 and 0.5 and at 30-minute intervals thereafter, blood samples were collected via an auricular artery, and serum concentrations of etorphine were determined by use of radioimmunoassay. The highest mean serum concentration of etorphine in 6 elephants given a single IM injection and subsequently maintained on halothane and oxygen was 1.62 +/- 0.97 ng/ml at postinjection hours 0.5; thereafter, the mean serum concentration decreased steadily. In 4 elephants maintained in lateral recumbency with multiple IV administrations of etorphine, a correlation was not found between the time to develop initial signs of arousal and serum concentrations of etorphine before arousal. After administration of the initial immobilizing dose of etorphine, the interval between successive IV administrations of etorphine decreased.     

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.     

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.     

Reversal of xylazine-induced sedation in llamas, using doxapram or 4-aminopyridine and yohimbine

For each of 3 separate evaluations, 6 fasted llamas (Lama glama) were sedated with xylazine (1.1 mg/kg of body weight, IV) and then 15 minutes later were given normal saline solution (5.0 ml, IV; control values), doxapram (2.2 mg/kg, IV), or 4-amino-pyridine (0.3 mg/kg, IV) and yohimbine (0.125 mg/kg, IV). After administration of 4-aminopyridine and yohimbine, the llamas stood in a mean of 11 minutes and resumed eating in a mean of 34 minutes; both means were significantly less (P less than 0.05) than control values (46 minutes and 67 minutes, respectively). Doxapram induced muscle fasciculations, and (compared with control values) did not significantly decrease the time to standing (41 minutes) or the time until the animals resumed eating (68 minutes). Yohimbine and 4-aminopyridine in combination rapidly antagonized xylazine-induced sedation in llamas, whereas doxapram was ineffective as an antagonist of xylazine-induced sedation.     

Anesthesia induced by administration of xylazine hydrochloride alone or in combination with ketamine hydrochloride and reversal by administration of yohimbine hydrochloride in captive Axis deer (Axis axis)

OBJECTIVE: To determine the anesthetic dose and cardiopulmonary effects of xylazine hydrochloride when used alone or in combination with ketamine hydrochloride and evaluate the efficacy of yohimbine hydrochloride to reverse anesthetic effects in captive Axis deer. ANIMALS: 35 adult (10 males and 25 females) Axis deer (Axis axis). PROCEDURES: All deer were anesthetized by IM administration of xylazine (3.5 mg/kg; experiment 1), a combination of ketamine and xylazine (1.25 and 1.5 mg/kg, respectively; experiment 2), or another combination of ketamine and xylazine (2.5 and 0.5 mg/kg, respectively; experiment 3). In addition, female deer were also anesthetized by IM administration of a third combination of ketamine and xylazine (1.5 and 1 mg/kg, respectively; experiment 4). Ten to 40 minutes after induction, anesthesia was reversed by IV administration of yohimbine (5, 8, or 10 mg). RESULTS: In male deer, experiment 3 yielded the most rapid induction of anesthesia. In females, experiment 4 yielded the best induction of anesthesia without adverse effects. All doses of yohimbine reversed anesthesia. Duration of anesthesia before administration of yohimbine had no effect on recovery time. CONCLUSIONS AND CLINICAL RELEVANCE: A combination of ketamine and xylazine can be used to induce anesthesia in Axis deer. Furthermore, anesthetic effects can be reversed by administration of yohimbine.     

Xylazine and tiletamine-zolazepam anesthesia in horses

The cardiopulmonary and anesthetic effects of xylazine in combination with a 1:1 mixture of tiletamine and zolazepam were determined in 6 horses. Each horse was given xylazine IV or IM, as well as tiletamine-zolazepam IV on 4 randomized occasions. Anesthetics were administered at the rate of 1.1 mg of xylazine/kg of body weight, IV, 1.1 mg of tiletamine-zolazepam/kg, IV (treatment 1); 1.1 mg of xylazine/kg, IV, 1.65 mg of tiletamine-zolazepam/kg, IV (treatment 2); 1.1 mg of xylazine/kg, IV, 2.2 mg of tiletamine-zolazepam/kg, IV (treatment 3); and 2.2 mg of xylazine/kg, IM, 1.65 mg of tiletamine-zolazepam/kg, IV (treatment 4). Tiletamine-zolazepam doses were the sum of tiletamine plus zolazepam. Xylazine, when given IV, was given 5 minutes before tiletamine-zolazepam. Xylazine, when given IM, was given 10 minutes before tiletamine-zolazepam. Tiletamine-zolazepam induced recumbency in all horses. Duration of recumbency in group 1 was 31.9 +/- 7.2 (mean +/- 1 SD) minutes. Increasing the dosage of tiletamine-zolazepam (treatments 2 and 3) significantly (P less than 0.05) increased the duration of recumbency. Xylazine caused significant (P less than 0.05) decreases in heart rate and cardiac output and significant (P less than 0.05) increases in central venous pressure and mean pulmonary artery pressure 5 minutes after administration. Respiratory rate was decreased. Arterial blood pressures increased significantly (P less than 0.05) after xylazine was administered IV in treatments 1 and 3, but the increases were not significant in treatment 2. Xylazine administered IM caused significant (P less than 0.05) increases in central venous pressure and significant (P less than 0.05) decreases in cardiac output.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.