Ketamine, Telazol, xylazine and detomidine. A comparative anesthetic drug combinations study in ponies.

This study was designed to assess the effects of 5 anesthetic drug combinations in ponies: (1) ketamine 2.75 mg/kg, xylazine 1.0 mg/kg (KX), (2) Telazol 1.65 mg/kg, xylazine 1.0 mg/kg (TX), (3) Telazol 2 mg/kg, detomidine 20 micrograms/kg (TD-20), (4) Telazol 2 mg/kg, detomidine 40 micrograms/kg (TD-40), (5) Telazol 3 mg/kg, detomidine 60 micrograms/kg (TD-60). All drugs were given iv with xylazine or detomidine preceding ketamine or Telazol by 5 min. Heart rate was decreased significantly from 5 min to arousal after TD-20 but only at 60 and 90 min after TD-40 and TD-60 respectively. Respiratory rate was decreased significantly for all ponies. Induction time did not differ between treatments. Duration of analgesia was 10 min for KX, 22.2 min for TX, 27.5 min for TD-20, 32.5 min for TD-40, and 70 min for TD-60. Arousal time was significantly longer with detomidine and Telazol. Smoothness of recovery was judged best in ponies receiving KX and TD-40. All ponies stood unassisted 30 min after signs of arousal.     

Does the induction agent affect the course of halothane anaesthesia in horses?

Four hundred and ninety horses were anaesthetised with halothane for clinical surgical or diagnostic procedures following induction with either detomidine/keta-mine, detomidine/thiopentone, xylazine/ketamine or guaiphenesin/thiopentone. Routine clinical monitoring was performed during anaesthesia. All horses developed hypotension (mean arterial pressures below 80 mm Hg) and respiratory depression (significant fall in respiratory rate and arterial carbon dioxide tension above 7 kPa (53 mm Hg)) consistent with the recognised effects of halothane. All anaesthetic procedures incorporating xylazine or detomidine resulted in lower pulse rates (28–35 per min) than after guaiphenesin/thiopentone (36–44 per min) and there was greater respiratory depression after techniques employing thiopentone rather than keta-mine. Development of hypotension was delayed after techniques using the α₂ adrenoceptor agonist agents (xylazine and detomidine), particularly detomidine. Prernedication with acepromazine did not affect any of the physiological variables measured after techniques employing detomidine. Recovery to standing was fastest after xylazine/ketamine (31±1 min) and slowest after detomidine/thiopentone (53±2 min). Recovery quality was best after detomidine/thiopentone and all techniques employing an α₂ adrenoceptor agonist agent resulted in smoother recovery than after guaiphenesin/thiopentone. This study demonstrates that most of the physiological effects of individual induction agents are overridden by the cardiovascular and respiratory depressant effects of halothane. The study also shows that detomidine is an acceptable sedative for use before general anaesthesia with halothane in horses.     

The parasympatholytic effects of atropine sulfate and glycopyrrolate in rats and rabbits.

Nine groups of rats (n = 5 per group) received an intramuscular (IM) injection of one of the following drugs or drug combinations: saline, atropine (0.05 mg/kg), glycopyrrolate (0.5 mg/kg), ketamine:xylazine (85:15 mg/kg), ketamine:detomidine (60:10 mg/kg), atropine:ketamine:xylazine (0.05: 85:15 mg/kg), glycopyrrolate: ketamine:xylazine (0.5:85:15 mg/kg), atropine:ketamine:detomidine (0.05: 60:10 mg/kg) or glycopyrrolate: ketamine:detomidine (0.5:60:10). Similarly six groups of rabbits (n = 5) received an IM injection of either saline, atropine (0.2 mg/kg), atropine (2 mg/kg), glycopyrrolate (0.1 mg/kg), ketamine:xylazine (35:10 mg/kg) or glycopyrrolate:ketamine:xylazine (0.1:35:10 mg/kg). In rats, atropine sulfate (0.05 mg/kg) and glycopyrrolate (0.5 mg/kg) produced an increase in heart rate for 30 and 240 min, respectively. In rabbits atropine sulfate at either 0.2 or 2.0 mg/kg did not induce a significant increase in heart rate, but glycopyrrolate (0.1 mg/kg) elevated the heart rate above saline treated animals for over 50 min. Both atropine and glycopyrrolate provided protection against a decrease in heart rate in rats anesthetized with ketamine: xylazine (85:15 mg/kg) or ketamine: detomidine (60:10 mg/kg); however, glycopyrrolate was significantly more effective in maintaining the heart rate within the normal range. Glycopprrolate also prevented a decrease in heart rate in rabbits anesthetized with ketamine:xylazine (35:5 mg/kg). Neither glycopyrrolate nor atropine influenced respiration rate, core body temperature or systolic blood pressure when used alone or when combined with the injectable anesthetic. Glycopyrrolate is an effective anticholinergic agent in rabbits and rodents and more useful as a preanesthetic agent than atropine sulfate in these animals.     

Sedative and physiologic effects of orally administered alpha 2-adrenoceptor agonists and ketamine in cats

OBJECTIVE: To compare efficacy of 3 regimens of orally administered sedatives and determine physiologic effects of 1 of these regimens in healthy cats. DESIGN: Prospective randomized study. ANIMALS: 34 cats. PROCEDURE: Cats were assigned to 1 of 3 groups that were treated by oral administration of detomidine and ketamine, xylazine and ketamine, or medetomidine and ketamine. Cats were monitored for degree of sedation at 5-minute intervals for 60 minutes. Physiologic effects in cats treated with detomidine and ketamine were measured at 5-minute intervals for 30 minutes and compared with effects in cats treated i.m. with detomidine and ketamine or xylazine and ketamine. RESULTS: All cats treated orally with detomidine and ketamine became laterally recumbent; sedation was more variable in the other 2 groups treated orally. Vomiting and excessive salivation were the only adverse effects. Bradycardia (heart rate < 145 beats/min) was detected at each evaluation time in cats treated orally with detomidine and ketamine and in all cats treated i.m. Minimal differences among groups were detected for heart and respiratory rates, rectal temperature, and hemoglobin oxygen saturation. CONCLUSIONS AND CLINICAL RELEVANCE: Oral administration of detomidine and ketamine is an effective method of sedating healthy cats and induces minimal physiologic effects that are similar to those resulting from i.m. administration of sedatives.     

Chemical restraint for surgery in the standing horse.

Chemical restraint can be a useful pharmacologic tool to assist the veterinarian performing surgery in the standing horse. The agents discussed impose minimal adverse side effects and are considered relatively safe when administered in the doses described. Acetylpromazine, the most widely used tranquilizer, produces mild sedation but no analgesia. The use of tranquilizers for surgical procedures requires the combined use of either a local anesthetic technique or a sedative-hypnotic or opiate to provide analgesia. Sedative-hypnotics such as xylazine and detomidine or opiates such as morphine and butorphanol are commonly used. The sedative-hypnotics also can induce deep CNS depression and may be sufficient alone for many procedures. Opiates may be used to supplement the analgesia produced by sedative-hypnotics or provide analgesia to the tranquilized horse. Opiates are not useful alone because of their potential to cause CNS excitement in the horse. The combination of detomidine and butorphanol is probably the most effective drug combination to facilitate painful surgery in the standing horse.     

Development and characterization of an equine behaviour chamber and the effects of amitraz and detomidine on spontaneous locomotor activity

This report describes the development of a behaviour chamber and the validation of the chamber to measure locomotor activity of a horse. Locomotor activity was detected by four Mini-beam sensors and recorded on a data logger every 5 min for 22 h. Horses were more active during daytime than in the evening, which was at least partially related to human activity in their surroundings. To validate the ability of the chambers to detect changes in activity, fentanyl citrate and xylazine HCl, agents well-characterized as a stimulant and a depressant, respectively, were administered to five horses. Fentanyl citrate (0.016 mg/kg) significantly increased locomotor activity which persisted for 30 min. Xylazine HCl (1 mg/kg) significantly reduced locomotor activity for 90 min. Amitraz produced a dose-dependent decrease in locomotor activity, lasting 75 min for the 0.05 mg/kg dose, 120 min for the 0.10 mg/kg dose, and 180 min for the 0.15 mg/kg dose. In a separate experiment, yohimbine administration immediately reversed the sedative effect of amitraz. This suggests there is a similarity in the mode of action of amitraz, xylazine and detomidine, as yohimbine acts primarily by blocking central α 2 -adrenoceptors that are stimulated by agents like xylazine. There was also a significant decrease in locomotor activity following injection of detomidine (0.02, 0.04 and 0.08 mg/kg) for 1.5, 3.5 and 5.0 h, respectively. The locomotor chamber is a useful, sensitive and highly reproducible tool for measuring spontaneous locomotor activity in the horse, which allows investigators to determine an agent's average time of onset, duration and intensity of effect on movement.     

Pharmacological evidence for the involvement of alpha-2 adrenoceptors in the sedative effect of detomidine, a novel sedative-analgesic

The sedative effect and mechanism of action of a novel imidazole derivative, detomidine, were studied in laboratory animals. Three methods were used to quantify drug-induced sedation: (i) decrease in spontaneous activity of mice; (ii) increase in barbiturate induced anaesthesia time in mice; (iii) loss of righting reflex in chicks. Clonidine and xylazine were included in the studies for comparison. The sedative potency of detomidine was shown to be approximately equal to that of clonidine and much higher than that of xylazine. In all tests, the sedative effect of detomidine was inhibited by antagonists of alpha-2 adrenoceptors (yohimbine, rauwolscine and idazoxan) but not by alpha-1 antagonists (prazosin, corynanthine). Furthermore, an ex vivo receptor binding study in the rat showed that detomidine-induced decrease in spontaneous activity was significantly correlated to [3H]clonidine but not to [3H]prazosin displacement in brain membranes. These results show that detomidine has potent sedative effects in mice, rats and chicks, and suggest that this action is mediated through stimulation of alpha-2 adrenoceptors.     

The effects of xylazine,detomidine, acepromazine and butorphanol on equine solid phase gastric emptying rate

The aim of this study was to measure the effects of specific commonly used sedative protocols on equine solid phase gastric emptying rate, using the 13C-octanoic acid breath test (13C-OABT). The gastric emptying of a standard 13C-labelled test meal was measured once weekly in 8 mature horses over two 4 week treatment periods. Each horse acted as its own control. In treatment Period 1, saline (2 ml i.v.), xylazine (0.5 mg/kg i.v.), detomidine (0.01 mg/kg i.v.) or detomidine/butorphanol combination (0.01/0.02 mg/kg i.v.) was administered in randomised order after ingestion of the test meal. During treatment Period 2, test meal consumption was followed by saline, xylazine (1.0 mg/kg i.v.), or detomidine (0.03 mg/kg i.v.) administration, or preceded by acepromazine (0.05 mg/kg i.m.) in randomised order. The 13C:12C ratio of sequential expiratory breath samples was determined by isotope ratio mass spectrometry, and used to measure the gastric half-emptying time, t 1/2, and duration of the lag phase, t lag, for each of the 64 tests. In treatment Period 1, detomidine/butorphanol prolonged both t 1/2 and t lag with respect to xylazine 0.5 mg/kg and the saline control (P < 0.05). In Period 2, detomidine 0.03 mg/kg delayed each parameter with respect to saline, acepromazine and xylazine 1.0 mg/kg (P < 0.001). Xylazine 1.0 mg/kg also lengthened t lag relative to the saline control (P = 0.0004), but did not cause a significant change in t 1/2. Comparison of treatment periods showed that the inhibitory effect of detomidine on gastric emptying rate was dose related (P<0.05). These findings may have clinical significance for case selection when these agents are used for purposes of sedation and/or analgesia.     

Cardiorespiratory and metabolic effects of xylazine, detomidine, and a combination of xylazine and acepromazine administered after exercise in horses

OBJECTIVE: To determine sedative, cardiorespiratory and metabolic effects of xylazine hydrochloride, detomidine hydrochloride, and a combination of xylazine and acepromazine administered i.v. at twice the standard doses in Thoroughbred horses recuperating from a brief period of maximal exercise. ANIMALS: 6 adult Thoroughbreds. PROCEDURE: Horses were preconditioned by exercising them on a treadmill to establish a uniform level of fitness. Each horse ran 4 simulated races, with a minimum of 14 days between races. Simulated races were run at a treadmill speed that caused horses to exercise at 120% of their maximal oxygen consumption. Horses ran until they were fatigued or for a maximum of 2 minutes. One minute after the end of exercise, horses were treated i.v. with xylazine (2.2 mg/kg of body weight), detomidine (0.04 mg/kg), a combination of xylazine (2.2 mg/kg) and acepromazine (0.04 mg/kg), or saline (0.9% NaCl) solution. Treatments were randomized so that each horse received each treatment once, in random order. Cardiopulmonary indices were measured, and samples of arterial and venous blood were collected immediately before and at specific times for 90 minutes after the end of each race. RESULTS: All sedatives produced effective sedation. The cardiopulmonary depression that was induced was qualitatively similar to that induced by administration of these sedatives to resting horses and was not severe. Sedative administration after exercise prolonged the exercise-induced increase in body temperature. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of xylazine, detomidine, or a combination of xylazine-acepromazine at twice the standard doses produced safe and effective sedation in horses that had just undergone a brief, intense bout of exercise.     

Alpha-2 agonist dissociative anesthetic combinations in fallow deer (Cervus dama).

Three anesthetic protocols, each using an alpha-2 agonist sedative in combination with a dissociative anesthetic, were evaluated in 17 captive fallow deer (Cervus dama). The alpha-2 agonist was given first in two of the three protocols: 1) detomidine (0.1-0.2 mg/kg i.m.) followed by tiletamine-zolazepam (3.0-6.3 mg/kg i.m.) and 2) xylazine (0.6-0.9 mg/kg i.m.) followed by tiletamine-zolazepam (4-5 mg/kg i.m.). In the third protocol, xylazine (1.0-6.2 mg/kg i.m.) and ketamine (2.5-5.1 mg/kg i.m.) were given simultaneously. Each of the sedative/anesthetic combinations produced acceptable immobilization in fallow deer and both provide an alternative to narcotic anesthesia.     

Effects of alpha-2 adrenoceptor agonists during recovery from isoflurane anaesthesia in horses

REASONS FOR PERFORMING STUDY: Recovery from inhalant anaesthesia in the horse is a critical and difficult period to manage; however, several factors could help to obtain a calm recovery period including choice of anaesthetic and analgesic procedure used and the conditions under which anaesthetic maintenance and recovery occur. OBJECTIVES: The objective of this study was to evaluate and compare the quality of recovery in horses administered saline, xylazine, detomidine or romifidine during recovery from isoflurane anaesthesia. METHODS: Six mature and healthy horses were premedicated with i.v. xylazine and butorphanol, and anaesthesia induced using ketamine. After 2 h of inhalant anaesthesia with isoflurane vaporised in oxygen, saline solution, xylazine (0.1 mg/kg bwt), detomidine (2 microg/kg bwt) or romifidine (8 pg/kg bwt) were administered. The quality of recovery of each horse and the degree of sedation and ataxia were evaluated. Cardiovascular and respiratory parameters were recorded, and arterial blood samples obtained and analysed for pH, PO2 and PCO2 during recovery. RESULTS: Quality of recovery was better in groups treated with alpha-2 adrenergic receptors agonists, showing less ataxia. Degree of sedation was greater in the romifidine group. CONCLUSIONS: We concluded that the administration of alpha-2 adrenoceptor agonists during recovery from isoflurane anaesthesia in horses prolonged and improved the quality of recovery without producing significant cardiorespiratory effects. POTENTIAL CLINICAL RELEVANCE: Administration of alpha-2 adrenoceptor agonists after inhalent anaesthesia could prevent complications during the recovery period.     

Interactions of xylazine and detomidine with alpha2-adrenoceptors in brain tissue from cattle,swine and rats

Xylazine is an alpha2-adrenoceptor agonist sedative with a much higher interspecies variability in effect than detomidine, another alpha2-agonist used in veterinary practice. In the present study, we have used radioligand binding in brain tissue to investigate if the high species variation in sensitivity to xylazine could be explained in terms of receptor interactions. Species known to be more (cattle) or less (swine and rats) sensitive to xylazine were used. There was no variation in the density or the subtype pattern of the alpha2-adrenoceptors that could explain the species variation recorded in vivo, as a homogenous population of the alpha2A/D-subtype (200-300 fmol/mg protein) was found in all species. The species differences in the affinities of xylazine and detomidine were minor and similar for the two drugs. The only parameter investigated where a significant species difference was found for xylazine but not for detomidine was the slope of the inhibition binding curve when the G-protein coupling was diminished. For xylazine this slope was considerably lower than unity (i.e. 0.77 +/- 0.075) using cattle preparations compared with 0.92 +/- 0.037 (mean +/- SE) and 0.90 +/- 0.028, respectively for swine and rats, while for detomidine this parameter was close to unity in all species (cattle, swine, rat). This finding indicates that the species variation in effect for xylazine could be due to differences at the G-protein level or further down-stream in the effect cascade.     

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.     

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.     

A comparison of the sedative effects of three α2-adrenoceptor agonists (romifidine, detomidine and xylazine) in the horse

The sedative effects of a new alpha 2-adrenoceptor agonist, romifidine, were compared with those of xylazine and detomidine. Five horses were treated with two doses of romifidine (40 micrograms/kg body weight and 80 micrograms/kg body weight), two doses of detomidine (10 micrograms/kg body weight and 20 micrograms/kg body weight) and one dose of xylazine (1 mg/kg body weight) given by intravenous injection using a Latin-square design. The dose of 80 micrograms/kg romifidine appeared equipotent to 1 mg/kg xylazine and 20 micrograms/kg detomidine, although at these doses both xylazine and detomidine had a shorter action. Detomidine 20 micrograms/kg and xylazine both produced greater lowering of the head and a greater degree of ataxia than romifidine at either dose. Romifidine produced sedation similar to that of the other drug regimes. The effect upon imposed stimuli was similar.     

A2-agonists in sheep: a review

OBJECTIVE: To review the use and adverse effects of alpha(2)-agonists in sheep. STUDY DESIGN: Literature review. MATERIAL AND METHODS: 'Pubmed' of the United States National Library of Medicine and 'Veterinary Science' of CAB International were searched for references relating sheep to alpha(2)-agonists. The bibliographies of retrieved articles were further scrutinized for pertinent references, and relevant articles were selected manually. RESULTS: Reports on the use of clonidine, xylazine, detomidine, romifidine, medetomidine and dexmedetomidine, MPV-2426 and ST-91 in sheep were found in the literature. Most of the studies described xylazine followed by medetomidine and clonidine. The literature on detomidine and romifidine in sheep was sparse. Reports included pharmacokinetic studies, evaluation of sedative, analgesic, and anaesthetic techniques with or without cardiovascular effects, and experimental investigations of adverse effects (mainly hypoxaemia) including the mechanisms of pulmonary oedema and impaired oxygenation after alpha(2)-agonist administration. CONCLUSIONS: A(2)-agonists are potent and effective analgesics in sheep. In combination with ketamine, they are frequently used for the induction and maintenance of anaesthesia, in this case analgesia is satisfactory. The degree of hypoxaemia which occurs with all commercially available alpha(2)-agonists is highly variable and depends on individual or breed-related factors; the most severe reactions occur after intravenous (IV) injection and during general anaesthesia. Clinical relevance Subclinical respiratory disease is common in sheep. Rapid IV injection of alpha(2)-agonists without supplementary oxygen should be avoided whenever hypoxaemia may be critical.     

The use of atropine to control heart rate responses during detomidine sedation in horses

Detomidine is a sedative-analgesic which has a pharmacological profile similar to xylazine. There is evidence that the sedative effects are mediated through alpha-2 adrenoceptors.Cardiopulmonary responses were determined using detomidine as the principal agent and as a preanesthetic prior to the induction of general anesthesia. Compatibility with guaifenesin, sodium thia-mylal and halothane were determined.As in the case of xylazine, detomidine produces a slowing of heart rates. This was found to be either sinus bradycardia or heart block. There may be a corresponding increase in systolic blood pressures. The respiratory pattern is altered through the arterial blood gases and pH data supported evidence of adequate ventilation. The heart rate response to detomidine without anticholinergic treatment was transient and related to he duration of drug action.Atropine sulfate, 0.02 mg/kg i.v. was effective in preventing or treating bradycardia or heart block from detomidine. Heart rates also increased during the administration of guaifenesin and sodium thia-mylal when given 50 min poisit-detomidine.     

A review of diazepam and its use in the horse

The application of diazepam in clinical equine practice has come into favor in recent years. This review covers the relevant studies concerning the pharmacological properties, pharmacodynamics and pharmacokinetics of diazepam and its clinical use in the horse. As a benzodiazepinic drug diazepam potentates GABA-mediated inhibition in the CNS. It exerts its principal action in the brain stem reticular formation and produces hypnotic, sedative, anxiolytic, anticonvulsant and skeletal muscle-relaxant effects. However, Diazepam is largely used in equine practice in combination with ketamine and xylazine hydrochloride for induction of anesthesia and alone as a sedative/ataractic/neuroleptic. We aimed to present a general discussion of the relevant data from pharmacokinetic, pharmacodynamic and clinical studies and subsequently to evaluate their results. The discussion is based on our results, reported partially in previous publications including an evaluation of the literature. Available knowledge concerning the pharmacology of diazepam and its application in the horse is presented. The relative merits and demerits of a variety of agents intended for use in horses are discussed, with the aim of providing practitioners and clinicians with a wider selection of safe drugs for equine sedation and premedication.     

Sedation and chemical restraint of deer

This review examines the properties of chemical immobilising agents of use or potential use in deer for velvet antler removal. The alpha-2-adrenergic agonist, xylazine, is the most commonly used agent for chemical restraint of stags for this purpose in New Zealand. This compound is often combined with an opioid or ketamine to enhance its effectiveness. Concerns about the carcinogenic potential of a xylazine metabolite have led to a call by the deer industry to limit the use of this drug and stimulated enquiry into alternatives. The potent pure opioid agonists, fentanyl, carfentanil and etorphine, are less effective than xylazine when used alone, and their use presents greater risk to operators and animals and is subject to more stringent legal restrictions. Newer alpha-2-adrenergic agonists, detomidine and medetomidine, are more potent than xylazine and unlikely to result in carcinogenic metabolites. Availability of specific alpha-2-adrenergic antagonists further enhances the usefulness of these drugs. The dissociative agent, ketamine, has proven useful for immobilisation of various domestic and wildlife species and captive species of deer but undesirable side effects and the low concentration, relative to the effective dose, of currently available formulations limit its usefulness. Combination of a dissociative agent with an alpha-2-adrenergic agent reduces the required dose of both and enhances their efficacy. A commercially available combination of the dissociative anaesthetic agent, tiletamine, and the benzodiazepine, zolazepam, is more potent than ketamine and induction times are faster. This combination can be manipulated to varying concentrations by dissolution with alpha-2-adrenergic agents. A long-acting neuroleptic agent, zuclopenthixol, has recently been investigated for calming deer and may be an alternative to classical sedative-immobilising agents. Most chemical immobilisation agents used alone or in combination produce respiratory depression and supplemental oxygen has been recommended. All would likely result in some form of chemical residues in velvet antler.