Evaluation of the sedative and clinical effects of xylazine,detomidine, medetomidine and dexmedetomidine in miniature donkeys

ABSTRACT

Aim: To evaluate the sedative and clinical effects of I/V xylazine, detomidine, medetomidine and dexmedetomidine in miniature donkeys.

Methods: Seven clinically healthy, male adult miniature donkeys with a mean age of 6 years and weight of 105?kg, were assigned to five I/V treatments in a randomised, cross-over design. They received either 1.1?mg/kg xylazine, 20?μg/kg detomidine, 10?μg/kg medetomidine, 5?μg/kg dexmedetomidine or saline, with a washout period of ≥7 days. The degree of sedation was scored using a 4-point scale by three observers, and heart rate (HR), respiration rate (RR), rectal temperature and capillary refill time (CRT) were recorded immediately before and 5, 10, 15, 30, 60, 90 and 120 minutes after drug administration.

Results: All saline-treated donkeys showed no sedation at any time, whereas the donkeys treated with xylazine, detomidine, medetomidine and dexmedetomidine had mild or moderate sedation between 5 and 60 minutes after treatment, and no sedation after 90 minutes. All animals recovered from sedation without complication within 2 hours. The mean HR and RR of saline-treated donkeys did not change between 0 and 120 minutes after administration, but the mean HR and RR of donkeys treated with xylazine, detomidine, medetomidine and dexmedetomidine declined between 5 and 60 minutes after drug administration. The mean rectal temperature of all treated donkeys did not change between 0 and 120 minutes after administration. The CRT for all donkeys was ≤2 seconds at all times following each treatment.

Conclusions and clinical relevance: Administration of xylazine at 1.1?mg/kg, detomidine at 20?μg/kg, medetomidine at 10?μg/kg and dexmedetomidine at 5?μg/kg resulted in similar sedation in miniature donkeys. Therefore any of the studied drugs could be used for sedation in healthy miniature donkeys.     

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.     

Cardiovascular effects of medetomidine, detomidine and xylazine in horses

The cardiovascular effects of medetomidine, detomidine, and xylazine in horses were studied. Fifteen horses, whose right carotid arteries had previously been surgically raised to a subcutaneous position during general anesthesia were used. Five horses each were given the following 8 treatments: an intravenous injection of 4 doses of medetomidine (3, 5, 7.5, and 10 microg/kg), 3 doses of detomidine (10, 20, and 40 microg/kg), and one dose of xylazine (1 mg/kg). Heart rate decreased, but not statistically significant. Atrio-ventricular block was observed following all treatments and prolonged with detomidine. Cardiac index (CI) and stroke volume (SV) were decreased with all treatments. The CI decreased to about 50% of baseline values for 5 min after 7.5 and 10 microg/kg medetomidine and 1 mg/kg xylazine, for 20 min after 20 microg/kg detomidine, and for 50 min after 40 microg/kg detomidine. All treatments produced an initial hypertension within 2 min of drug administration followed by a significant decrease in arterial blood pressure (ABP) in horses administered 3 to 7.5 microg/kg medetomidine and 1 mg/kg xylazine. Hypertension was significantly prolonged in 20 and 40 microg/kg detomidine. The hypotensive phase was not observed in 10 microg/kg medetomidine or detomidine. The changes in ABP were associated with an increase in peripheral vascular resistance. Respiratory rate was decreased for 40 to 120 min in 5, 7.5, and 10 microg/kg medetomidine and detomidine. The partial pressure of arterial oxygen decreased significantly in 10 microg/kg medetomidine and detomidine, while the partial pressure of arterial carbon dioxide did not change significantly. Medetomidine induced dose-dependent cardiovascular depression similar to detomidine. The cardiovascular effects of medetomidine and xylazine were not as prolonged as that of detomidine. KEY WORDS: cardiovascular effect, detomidine, equine, medetomidine, xylazine.     

Some factors influencing the level of clinical sedation induced by medetomidine in rabbits

Rabbits (n=23) received intravenous bolus medetomidine at 100 mug/kg. Prior to medetomidine administration, heart and respiratory rates were measured, arterial blood was collected and analysed for plasma cortisol, glucose and albumin concentrations. Fifteen minutes after medetomidine administration, heart and respiratory rates were measured again and sedation was scored. The rabbit was afterwards anaesthetized with 20 mg/kg ketamine administered intravenously to enable spinal tap and heart puncture. Cerebrospinal fluid (CSF) was collected (this occurred 20 min post medetomidine administration) and analysed for medetomidine concentration. Blood was collected by heart puncture immediately after the spinal tap and analysed for serum medetomidine concentration. Cerebrospinal fluid medetomidine concentration correlated negatively with sedation. Serum medetomidine correlated positively with CSF medetomidine concentration. Cerebro-spinal fluid medetomidine was 17 +/- 13% of serum medetomidine concentration. Plasma cortisol and glucose concentrations correlated negatively with serum medetomidine. We conclude that after an intravenous bolus administration of a low sedative dose of medetomidine to rabbits; CSF concentration of the drug correlate negatively with sedation and that this may be because of the fact that only the free and unbound medetomidine may be available for detection in the CSF, the concentration of medetomidine detected in the CSF was much lower than that in blood and a positive correlation exists between CSF and serum medetomidine concentrations. Stress may have some effect on the distribution or metabolism of medetomidine in rabbits.     

Sedative and cardiopulmonary effects of medetomidine hydrochloride and xylazine hydrochloride and their reversal with atipamezole hydrochloride in calves

OBJECTIVE: To assess the sedative and cardiopulmonary effects of medetomidine and xylazine and their reversal with atipamezole in calves. ANIMALS: 25 calves. PROCEDURES: A 2-phase (7-day interval) study was performed. Sedative characteristics (phase I) and cardiopulmonary effects (phase II) of medetomidine hydrochloride and xylazine hydrochloride administration followed by atipamezole hydrochloride administration were evaluated. In both phases, calves were randomly allocated to receive 1 of 4 treatments IV: medetomidine (0.03 mg/kg) followed by atipamezole (0.1 mg/kg; n = 6), xylazine (0.3 mg/kg) followed by atipamezole (0.04 mg/kg; 7), medetomidine (0.03 mg/kg) followed by saline (0.9% NaCl; 6) solution (10 mL), and xylazine (0.3 mg/kg) followed by saline solution (10 mL; 6). Atipamezole or saline solution was administered 20 minutes after the first injection. Cardiopulmonary variables were recorded at intervals for 35 minutes after medetomidine or xylazine administration. RESULTS: At the doses evaluated, xylazine and medetomidine induced a similar degree of sedation in calves; however, the duration of medetomidine-associated sedation was longer. Compared with pretreatment values, heart rate, cardiac index, and PaO(2) decreased, whereas central venous pressure, PaCO(2), and pulmonary artery pressures increased with medetomidine or xylazine. Systemic arterial blood pressures and vascular resistance increased with medetomidine and decreased with xylazine. Atipamezole reversed the sedative and most of the cardiopulmonary effects of both drugs. CONCLUSIONS AND CLINICAL RELEVANCE: At these doses, xylazine and medetomidine induced similar degrees of sedation and cardiopulmonary depression in calves, although medetomidine administration resulted in increases in systemic arterial blood pressures. Atipamezole effectively reversed medetomidine- and xylazine-associated sedative and cardiopulmonary effects in calves.     

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.     

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.     

Medetomidine, a new sedative-analgesic for use in the dog and its reversal with atipamezole

The sedative and physiological effects of intramuscular medetomidine (20 and 40 μg/kg) in dogs were compared with those of xylazine (2 mg/kg). The efficacy of atipamezole (200 μg/kg), as an antagonist given 15 or 45 minutes after medetomidine (40 μg/kg) was studied. Following medetomidine, onset of sedation was rapid, and depth and duration of sedation were dose dependent. The higher dose produced jaw relaxation, depression of the pedal reflex, downward rotation of the eye and dogs could be positioned for radiography of the hips. Side effects were similar after either medetomidine or xylazine, and included bradycardia, a fall in respiratory rate and muscle tremor. Vomiting during induction was less frequent after medetomidine than after xylazine. Intramuscular administration of atipamezole rapidly reversed the sedative effects of medetomidine. Signs of arousal were seen within three minutes; all dogs could stand within 10 minutes and appeared clinically normal. Heart and respiratory rates rose, but did not return to presedation values. Relapse to sedation was not noted.     

Detomidine-diazepam-ketamine anaesthesia in buffalo (Bubalus bubalis) calves

Eight buffalo calves (8-12 months, 70-100 kg) were randomly assigned to two groups of four animals each. Animals of group I were given detomidine (100 micrograms/kg), whereas animals of group II received a mixture of detomidine (100 micrograms/kg), diazepam (100 micrograms/kg) and ketamine (3 mg/kg) (DDK) intravenously. Various clinical parameters, such as weak time, down time, pedal and pinprick reflexes, muscle relaxation and extent of sedation, as well as heart and respiratory rates and electrocardiograms were measured before (time 0) and 15, 30, 45, 60, 75 and 90 min after treatment. In all the animals of group II (DDK), the pedal reflex was completely abolished (score: 3.00 +/- 0.00) within 5 min, the pinprick response was either very weak or it was completely abolished at this interval. Muscle relaxation and sedation were excellent within 5 min of DDK administration. The depth of sedation and analgesia was maximum from 5 to 15 min postinjection. Detomidine alone, however, failed to produce appropriate depression of the pedal and pinprick reflexes, sedation was mild and muscle relaxation was inadequate. Heart rate showed a significant (P < 0.05) decrease in group I, but the decrease was non-significant in group II. A more pronounced increase in respiratory rate was observed in group I as compared to group II. Animals of both groups recovered within 90 min without any complication. Minimal changes in the cardiovascular system in the group given the DDK combination were an advantage over the group given detomidine. The results indicated that DDK combination is safe and suitable for 15 min of anaesthesia with excellent muscle relaxation and has only limited cardiorespiratory effects in buffaloes.     

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.     

Xylazine-Ketamine and Detomidine-Tiletamine-Zolazepam Anesthesia in Horses

Eight horses were anesthetized three times, by intravenous administration of xylazine (1.1 mg/kg) and ketamine (2.2 mg/kg), detomidine (0.02 mg/kg) and tiletamine-zolazepam (1.1 mg/kg), or detomidine (0.04 mg/kg) and tiletamine-zolazepam (1.4 mg/kg). The sequences were randomized. The duration of analgesia and the times to sternal and standing positions were recorded. Heart rate, arterial pressure, pHa, PaCO2, and PaO2 were measured before and during anesthesia. The duration of analgesia with the two doses of detomidine-tiletamine-zolazepam, 26 +/- 4 minutes and 39 +/- 11 minutes, respectively, was significantly longer than the 13 +/- 6 minutes obtained with xylazine-ketamine. Bradycardia occurred after administration of detomidine, but heart rates returned to baseline values 5 minutes after administration of tiletamine and zolazepam. Arterial pressure was significantly higher and PaO2 significantly lower during anesthesia with detomidine-tiletamine-zolazepam than with xylazine-ketamine. Some respiratory acidosis developed with all anesthetic combinations. The authors conclude that detomidine-tiletamine-zolazepam can provide comparable anesthesia of a longer duration than xylazine and ketamine, but hypoxemia will develop in some horses.     

Effect of medetomidine and its antagonism with atipamezole on stress-related hormones, metabolites, physiologic responses, sedation, and mechanical threshold in goats

OBJECTIVE: To evaluate the effects of medetomidine and its antagonism with atipamezole in goats. STUDY DESIGN: Prospective randomized crossover study with 1 week between treatments. ANIMALS: Six healthy 3-year-old neutered goats (three male and three female) weighing 39.1-90.9 kg (60.0 +/- 18 kg, mean +/- SD). METHODS: Goats were given medetomidine (20 microg kg(-1), IV) followed, 25 minutes later, by either atipamezole (100 microg kg(-1), IV) or saline. Heart and respiratory rate, rectal temperature, indirect blood pressure, and mechanical threshold were measured, and sedation and posture were scored and blood samples obtained to measure epinephrine, norepinephrine, free fatty acids, glucose, and cortisol concentrations at baseline (immediately before medetomidine), 5 and 25 minutes after medetomidine administration, and at 5, 30, 60, and 120 minutes after the administration of antagonist or saline. Parametric and nonparametric tests were used to evaluate data; p < 0.05 was considered significant. RESULTS: Medetomidine decreased body temperature, heart rate, and respiratory rate and increased mean arterial blood pressure, cortisol, and glucose. Recumbency occurred 89 +/- 50 seconds after medetomidine administration. All goats were standing 86 +/- 24 seconds after atipamezole administration whereas all goats administered saline were sedate and recumbent at 2 hours. Tolerance to compression of the withers and metacarpus increased with medetomidine. From 5 to 120 minutes after saline or atipamezole administration, there were differences in body temperature, glucose, and cortisol but none in heart rate or blood pressure. Three of the six goats receiving saline developed bloat; five of six urinated. After atipamezole, four of six goats developed piloerection and all goats were agitated and vocalized. CONCLUSION: At the doses used, atipamezole antagonized the effects of medetomidine on recumbency, sedation, mechanical threshold, and the increase in glucose. Atipamezole increased the rate of return of cortisol toward baseline, and prevented further decline in rectal body temperature. CLINICAL RELEVANCE: Atipamezole may be used to antagonize some, but not all effects of medetomidine.     

Sedative effects of medetomidine in pigs.

Sedative effects of medetomidine, a potent selective and specific alpha 2-adrenoceptor agonist, were evaluated in pigs using 5 different doses (30, 50, 80, 100 and 150 micrograms/kg of body weight) and compared with those of xylazine (2 mg/kg). Atropine (25 micrograms/kg) was mixed with both drugs to prevent severe bradycardia. All drugs were administered intramuscularly. Medetomidine at a dosage of 30 micrograms/kg produced more potent sedation than xylazine. The depth of sedation induced by medetomidine was dose dependent within the range from 30 to 80 micrograms/kg. At 100 or 150 micrograms/kg, the depth of sedation was mostly the similar level to that at 80 micrograms/kg but the duration was prolonged. The degree of muscle relaxation produced by medetomidine also seemed to be dose dependent from 30 to 80 micrograms/kg and was stronger than that produced by xylazine. An increase in the duration of muscle relaxation was dose dependent up to 150 micrograms/kg. No analgesic effect was produced by xylazine, however moderate analgesia was obtained by medetomidine. There were no marked changes in heart rate and respiratory rate during the observation period in pigs of any groups, however mild hypothermia after the administration of both drugs was observed. From these results, medetomidine has a significant and dose-dependent sedative effects which are much more potent than that of xylazine, and a combination of 80 micrograms/kg of medetomidine and 25 micrograms/kg of atropine is suitable for sedation with lateral recumbency and moderate muscle relaxation without notable side effects in pigs.     

The use of a medetomidine, butorphanol and atropine combination to enable blood sampling in young pigs

AIM: To determine the suitability of a reversible, injectable anaesthetic combination including medetomidine, butorphanol and atropine to produce the degree of immobilisation required to allow blood sampling in young pigs. METHODS: Twenty 6-week-old crossbred, intact male pigs were sedated with an intramuscular (I/M) injection of 80 microg/kg medetomidine, 200 microg/kg butorphanol and 25 microg/kg atropine. Heart and respiratory rates and rectal temperatures were monitored. Excessive salivation, gagging, laryngeal reflex, presence of pedal reflex and deep and surface analgesia were noted. Time of injection and the time when pigs reached mild and full sedation were also recorded. RESULTS: Mild sedation was produced in 90% of pigs after 5.6 (SEM 0.96) min (n = 18; median 5, range 2-16 min), and full sedation (lateral recumbency and loss of jaw tone) in 60% of pigs after 12.5 (SEM 2.14) min (n = 12; median 10, range 5-28 min). The depth and duration of sedation were very variable and most animals were easily aroused. Ninety percent of the animals required the administration of halothane by mask to allow blood sampling, but the amount of halothane required was small. Heart and respiratory rates decreased (p < 0.001) but remained within the normal range. Rectal temperature was above normal at the time of sedation and at the time of blood sampling when the ambient temperature was 29 degrees C but not when the ambient temperature was reduced to 25 degrees C. CONCLUSIONS: The combination of medetomidine, butorphanol and atropine at these doses produced sedation of variable depth and duration that was insufficient on its own to allow blood sampling in the majority of pigs. Hyperthermia can occur in temperature-controlled environments when using medetomidine, butorphanol and atropine in pigs. Reduction of stress and a quieter environment may improve the effects of the anaesthetic combination.     

Cardiopulmonary and sedative effects of intravenous administration of low doses of medetomidine and xylazine to adult horses

OBJECTIVE: To determine the cardiopulmonary and sedative effects of medetomidine hydrochloride in adult horses and to compare those effects with effects of an equipotent dose of xylazine hydrochloride. ANIMALS: 10 healthy adult female horses. PROCEDURE: 5 horses were given medetomidine (4 microg/kg of body weight, i.v.), and the other 5 were given xylazine (0.4 mg/kg, i.v.). Heart rate, respiratory rate, arterial blood pressures, pulmonary arterial blood pressures, and cardiac output were recorded, and sedation and ataxia scores were assigned before and every 5 minutes after drug administration for 60 minutes. Rectal temperature and blood gas partial pressures were measured every 15 minutes after drug administration. RESULTS: Arterial blood pressure was significantly decreased throughout the study among horses given medetomidine and was significantly decreased for 40 minutes among horses given xylazine. Compared with baseline values, cardiac output was significantly decreased 10, 20, and 40 minutes after administration of medetomidine and significantly increased 40 and 60 minutes after administration of xylazine. Despite the significant decrease in respiratory rate in both groups, results of blood gas analyses were not significantly changed over time. Ataxia and sedation scores were of similar magnitude for the 2 groups, but ataxia persisted slightly longer among horses given medetomidine. Horses resumed eating hay 10 to 55 minutes after drug administration. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that equipotent low doses of medetomidine and xylazine induce comparable levels of ataxia and sedation and similar cardiopulmonary changes in adult horses.     

Tachypnea and Antipyresis in Febrile Horses after Sedation with α2‐Agonists

Background: Signs of tachypnea after sedation of febrile horses with α₂‐agonists have been noted previously but have not been further investigated. Objectives: To examine the effects of xylazine and detomidine on respiratory rate and rectal temperature in febrile horses and to investigate if either drug would be less likely than the other to cause changes in these variables. Animals: Nine febrile horses and 9 healthy horses were included in the study. Methods: Horses were randomly assigned to sedation with xylazine 0.5 mg/kg or detomidine 0.01 mg/kg. Heart rate and respiratory rate were recorded before sedation and at 1, 3, and 5 minutes after injection. Hourly measurements of rectal temperature were performed starting before sedation. Results: All febrile horses experienced an episode of tachypnea and antipyresis after sedation. Rectal temperature in the febrile group was significantly lower at 1, 2, and 3 hours after sedation. In several measurements, the decrease was >1°C. Respiratory rate in the febrile group was significantly increased after sedation. All febrile horses were breathing >40 breaths/min and 3 horses >100 breaths/min 5 minutes after sedation. No differences were noted between the 2 treatments. No significant changes in respiratory rate or temperature were noted in the reference group. Conclusions and Clinical Importance: Febrile horses can become tachypneic after sedation with detomidine or xylazine. The antipyretic properties of α₂‐agonists need consideration when evaluating patients that have been sedated several hours before examination.     

Comparison of detomidine hydrochloride, xylazine, and xylazine plus morphine in horses: a double blind study

Detomidine (30 mcg/kg), xylazine (1.1 mg/kg) and xylazine/morphine (1.1 mg/kg and 0.75 mg/kg with 300 mg maximum dose) were compared in horses admitted for broncho-alveolar lavage. Horses (n=99) were randomized and clinicians performing the procedure were unaware of the sedation used. Horses were assessed during the procedure and for the next 2 hours. A significant number of xylazine/morphine-sedated horses showed excitement (p<0.05). The frequency of sinus block or arrest and second-degree atrioventricular block was significantly greater with detomidine. Detomidine-sedated horses were significantly more depressed than either xylazine or xylazine/morphine treated animals. Heart rate was significantly greater in horses given xylazine/morphine by 60 min. There was no significant difference between drug treatments related to reactions to the procedure or respiratory rate depression. The study indicated that all three methods are suitable for standing restraint. The more frequent adverse side effects (circling, muscle fasciculations, head pressing) accompanying xylazine/morphine should be considered.     

Anaesthesia with midazolam/medetomidine/fentanyl in chinchillas (Chinchilla lanigera) compared to anaesthesia with xylazine/ketamine and medetomidine/ketamine

We studied four different drug regimes for anaesthetic management in chinchillas and evaluated and compared their cardiovascular and respiratory effects. In this randomized, cross-over experimental study, seven adult chinchillas, five females, two males [515 +/- 70 (SD) g] were randomly assigned to one of the following groups: group 1 [midazolam, medetomidine and fentanyl (MMF), flumazenil, atipamezole and naloxone (FAN); MMF-FAN] received 1.0 mg/kg midazolam, 0.05 mg/kg medetomidine and 0.02 mg/kg fentanyl i.m., and for reversal 0.1 mg/kg flumazenil, 0.5 mg/kg atipamezole and 0.05 mg/kg naloxone s.c. after 45 min; group 2 (MMF) 1.0 mg/kg midazolam, 0.05 mg/kg medetomidine and 0.02 mg/kg fentanyl i.m.; group 3 [xylazine/ketamine (X/K)] 2.0 mg/kg xylazine and 40.0 mg/kg ketamine i.m.; and group 4 [medetomidine/ketamine (M/K)] 0.06 mg/kg medetomidine and 5.0 mg/kg ketamine i.m. Reflexes were judged to determine anaesthetic stages and planes. Anaesthesia with X/K and M/K was associated with a prolonged surgical tolerance and recovery period. By reversing MMF, recovery period was significantly shortened (5 +/- 1.3 min versus 40 +/- 10.3 min in MMF without FAN, 73 +/- 15.0 min in X/K, and 31 +/- 8.5 min in M/K). Without reversal, MMF produced anaesthesia lasting 109 +/- 16.3 min. All combinations decreased respiratory and heart rate but compared with X/K and M/K, respiratory and cardiovascular complications were less in the MMF groups. Focussing on the clinical relevance of the tested combinations, completely reversible anaesthesia showed two major advantages: anaesthesia can be antagonized in case of emergency and routinely shortens recovery. In small animals particularly these advantages lead to less complications and discomfort and thus often can be lifesaving. As all analgesic components (medetomidine and fentanyl) are reversed, postoperative analgesia should be provided before reversal of anaesthesia.     

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.     

The use of a medetomidine,butorphanol and atropine combination to enable blood sampling in young pigs

AIM: To determine the suitability of a reversible, injectable anaesthetic combination including medetomidine, butorphanol and atropine to produce the degree of immobilisation required to allow blood sampling in young pigs.

METHODS: Twenty 6-week-old crossbred, intact male pigs were sedated with an intramuscular (I/M) injection of 80 µ'g/kg medetomidine, 200 µ'g/kg butorphanol and 25 µ'g/kg atropine. Heart and respiratory rates and rectal temperatures were monitored. Excessive salivation, gagging, laryngeal reflex, presence of pedal reflex and deep and surface analgesia were noted. Time of injection and the time when pigs reached mild and full sedation were also recorded.

RESULTS: Mild sedation was produced in 90% of pigs after 5.6 (SEM 0.96) min (n=18; median 5, range 2–16 min), and full sedation (lateral recumbency and loss of jaw tone) in 60% of pigs after 12.5 (SEM 2.14) min (n=12; median 10, range 5-28 min). The depth and duration of sedation were very variable and most animals were easily aroused. Ninety percent of the animals required the administration of halothane by mask to allow blood sampling, but the amount of halothane required was small. Heart and respiratory rates decreased (p<0.001) but remained within the normal range. Rectal temperature was above normal at the time of sedation and at the time of blood sampling when the ambient temperature was 29° C but not when the ambient temperature was reduced to 25°C.

CONCLUSIONS: The combination of medetomidine, butorphanol and atropine at these doses produced sedation of variable depth and duration that was insufficient on its own to allow blood sampling in the majority of pigs. Hyperthermia can occur in temperature-controlled environments when using medetomidine, butorphanol and atropine in pigs. Reduction of stress and a quieter environment may improve the effects of the anaesthetic combination.