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.     

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.     

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

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

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.     

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.     

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.     

Evaluation of Nociception,Sedation, and Cardiorespiratory Effects of a Constant Rate Infusion of Xylazine Alone or in Combination with Lidocaine in Horses

This study aimed to evaluate the effects of a constant rate infusion (CRI) of xylazine or xylazine in combination with lidocaine on nociception, sedation, and physiologic values in horses. Six horses were given intravenous (IV) administration of a loading dose (LD) of 0.55 mg/kg of xylazine followed by a CRI of 1.1 mg/kg/hr. The horses were randomly assigned to receive three treatments, on different occasions, administered 10 minutes after initiation of the xylazine CRI, as follows: control, physiologic saline; lidocaine low CRI (LLCRI), lidocaine (LD: 1.3 mg/kg, CRI: 0.025 mg/kg/min); and lidocaine high CRI (LHCRI), lidocaine (LD: 1.3 mg/kg, CRI: 0.05 mg/kg/min). A blinded observer assessed objective and subjective data for 50 minutes during the CRIs. In all treatments, heart and respiratory rates decreased, end-tidal carbon dioxide concentration increased, and moderate to intense sedation was observed, but no significant treatment effect was detected in these variables. Ataxia was significantly higher in LHCRI than in the control treatment at 20 minutes of infusion. Compared with baseline values, nociceptive threshold increased to as much as 79% in the control, 190% in LLCRI, and 158% in LHCRI. Nociceptive threshold was significantly higher in LLCRI (at 10 and 50 minutes) and in LHCRI (at 30 minutes) than in the control treatment. The combination of CRIs of lidocaine with xylazine produced greater increases in nociceptive threshold compared with xylazine alone. The effects of xylazine on sedation and cardiorespiratory variables were not enhanced by the coadministration of lidocaine. The potential to increase ataxia may contraindicate the clinical use of LHCRI, in combination with xylazine, in standing horses.     

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.     

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

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

Evaluation of Pentobarbital as a Drug for Standing Sedation in Cattle

Pentobarbital (1.0, 1.5, and 2.0 mg/kg intravenously [IV]) was administered to four adult cows to determine a dose suitable for producing standing sedation in adult cattle, and to evaluate its effects on cardiopulmonary function and rumen motility. The response was assessed after 15, 30, 60, and 90 minutes. The 1.0 and 1.5 mg/kg doses induced mild sedation at 15 and 30 minutes, and no sedation at 60 and 90 minutes. The 2.0 mg/kg dose produced moderate sedation at 15 and 30 minutes, and mild sedation at 60 minutes. The 2.0 mg/kg dose was judged to be the most suitable. The effects of pentobarbital (2.0 mg/kg IV) on heart rate, blood pressure, respiratory rate, blood gases, and rumen motility were measured in five cows during a 90 minute period. Respiratory rate was significantly depressed at 15, 30, and 60 minutes, but there were no significant changes in the other variables. Pentobarbital (2.0 mg/kg IV) is reliable in adult cattle for standing sedation of short duration.     

A Comparison of Xylazine–Diazepam–Ketamine and Xylazine–Guaifenesin–Ketamine in Equine Anesthesia

After sedation with xylazine (0.3 mg/kg intravenously [IV]), anesthesia was induced in six healthy horses with ketamine (2.0 mg/kg IV) and guaifenesin (100 mg/kg IV), diazepam (0.05 mg/kg IV), or diazepam (0.10 mg/kg IV). Anesthesia was maintained with halothane for 30 minutes. Heart rate, respiratory rate, direct arterial blood pressure, arterial blood gas, and pH measurements were made before, and at set intervals after, induction of anesthesia. Quality and characteristics of induction and recovery were evaluated objectively by an independent observer unaware of the protocol used. There were no significant differences among the three protocols from pre-induction values for arterial blood pressure, blood gas values, and pH. There was significantly greater ataxia at induction with the use of guaifenesin. The nature of induction, transition to and recovery from general anesthesia were comparable between guaifenesin and the higher dose of diazepam. Because of movements and difficulty with intubation, the lower dose of diazepam was considered unsatisfactory. It was concluded that diazepam (0.10 mg/kg) could be substituted for guaifenesin (100 mg/kg) to produce comparable quality of anesthesia in horses.     

Clinical use of yohimbine as an antagonist of xylazine depression of the central nervous system in cats

Antagonizing effects of various doses of yohimbine on a xylazine depression of the cerebroneural system (CNS) were studied in cats. Administration of various doses of yohimbine was investigated with respect to its antagonizing effects on various doses of xylazine. The time of CNS depression induced by commonly recommended doses of xylazine (2-4 mg/kg live weight) was shortened statistically significantly by intramuscular injections of yohimbine at a dose of 3 mg per kg live weight. After this yohimbine dose, the animals recovered consciousness already 10-15 minutes from application, with the complete resumption of reflexes. Preventive administration of the same dose of yohimbine hindered reliably the full development of CNS depression after the two xylazine doses (2 and 4 mg/kg live weight).     

Cardiopulmonary effects of xylazine and yohimbine in laterally recumbent sheep.

The effects of yohimbine (0.125 mg/kg) on cardiopulmonary parameters in six adult, xylazine treated (0.15 mg/kg), laterally recumbent sheep were studied. Following collection of baseline data, xylazine was administered intravenously and data were collected five and fifteen minutes later. At twenty minutes post-xylazine either yohimbine (0.125 mg/kg) or saline was given and further collection of data occurred at 25, 30, 40 and 50 minutes. Xylazine administration resulted in significant (P less than 0.05) respiratory depression, as reflected by a decrease in arterial oxygen partial pressure (PaO2). No significant changes in haemodynamic variables were observed. Yohimbine produced a significant improvement in PaO2 at the 50 minute period and abolished the paradoxical respiratory pattern when present. The results indicated that yohimbine can be used as an antagonist to control the duration of xylazine induced respiratory depression, although the degree of reversal was less than is clinically desirable.     

Influence of tolazoline on caudal epidural administration of xylazine in cattle

Eight adult female cattle (6 Holstein, 1 Jersey, 1 Brown Swiss) were used to determine the antagonistic effects of tolazoline, and alpha 2-adrenoceptor antagonist, on xylazine-induced (via caudal epidural administration) depression of CNS, respiratory, and cardiovascular activity and rumen motility. A 2% solution of xylazine HCl was injected into the epidural space at the first coccygeal interspace, using a dosage of 0.05 mg/kg of body weight, diluted to a 5-ml volume with sterile water, and administered at a rate of approximately 1 ml/30 s. Eight minutes after xylazine injection, either tolazoline (0.3 mg/kg) or saline solution (4 ml) was administered IV. All 8 cattle were treated, using both regimens in a random sequence; at least 1 week elapsed between treatments. Epidurally administered xylazine induced caudal analgesia (S3 to coccyx), as evaluated by no response to superficial and deep muscular pinprick, and induced sedation, cardiopulmonary depression, and inhibition of rumen motility, but all cattle remained standing. Tolazoline effectively reversed xylazine-induced rumen hypomotility, and partially antagonized xylazine-induced cardiopulmonary depression without affecting sedation and desirable local (S3 to coccyx) analgesic effects.     

Effect of yohimbine on xylazine-ketamine anesthesia in cats

Xylazine and ketamine are an anesthetic combination used in feline practice for routine surgical procedures. In a controlled study, we evaluated the effects of yohimbine, an antagonist of xylazine, on the anesthesia induced by this anesthetic combination in cats. Two intramuscular doses of xylazine and ketamine (2.2 mg of xylazine/kg plus 6.6 mg of ketamine/kg and 4.4 mg of xylazine/kg plus 6.6 mg of ketamine/kg) caused approximately 60 and 100 minutes of anesthesia, respectively, in control cats. When yohimbine (0.1 mg/kg) was given intravenously 45 minutes after ketamine administration, the cats regained consciousness within 3 minutes. They were ambulatory 1 to 2 minutes after regaining consciousness. Yohimbine also reversed the bradycardia and respiratory depression elicited by xylazine-ketamine. The results indicated that yohimbine may be useful for controlling the duration of xylazine-ketamine anesthesia in cats.     

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.     

Comparison of thiopentone/guaifenesin, ketamine/guaifenesin and ketamine/midazolam for the induction of horses to be anaesthetised with isoflurane

Forty-eight horses subjected to elective surgery were randomly assigned to three groups of 16 horses. After premedication with 0.1 mg/kg acepromazine intramuscularly and 0.6 mg/kg xylazine intravenously, anaesthesia was induced either with 2 g thiopentone in 500 ml of a 10 per cent guaifenesin solution, given intravenously at a dose of 1 ml/kg (group TG), or with 100 mg/kg guaifenesin and 2.2 mg/kg ketamine given intravenously (group KG), or with 0.06 mg/kg midazolam, and 2.2 mg/kg ketamine given intravenously (group KM). Anaesthesia was maintained with isoflurane. The mean (sd) end tidal isoflurane concentration (per cent) needed to maintain a light surgical anaesthesia (stage III, plane 2) was significantly lower in group KM (0.91 [0.03]) than in groups TG (1.11 [0.03]) and KG (1.14 [0.03]). The mean (sd) arterial pressure (mmHg) was significantly lower in group KG (67.4 [2.07]) than in groups TC (75.6 [2.23]) and KM (81.0 [2.16]). There were no significant differences in the logarithm of the heart rate, recovery time or quality of recovery between the three induction groups. However, pronounced ataxia was observed in the horses of group KM, especially after periods of anaesthesia lasting less than 75 minutes.     

The Reliability of Endoscopic Examination in Assessment of Arytenoid Cartilage Movement in Horses Part II. Influence of Side of Examination, Reexamination, and Sedation

Twenty Thoroughbred and Standardbred horses underwent endoscopic evaluation of arytenoid cartilage movement twice within 1 week. Each time, a flexible endoscope was passed without sedation through the right nostril and the left nostril, and through the right nostril 5 minutes after administration of xylazine hydrochloride (0.55 mg/kg or 1.1 mg/kg intravenously). Laryngeal cartilage movement was videorecorded. All videotaped images were reviewed by three veterinarians and subjectively placed in one of four grades. The intraobserver agreement rate varied from 52.6% for examination under sedation with 1.1 mg/kg of xylazine to 89.5% for unsedated reexamination through the left nostril. The effect of the various observations on median laryngeal grade was calculated. Examination under xylazine hydrochloride at either dosage yielded a change in median laryngeal grade from the unsedated examination in 45% of the evaluations. Reevaluation through the right or left nostril resulted in a different median laryngeal grade in 21% and 5% of the examinations, respectively. Objective measurements of the rima glottidis obtained by computer-assisted morphometric analysis of the recorded laryngeal images allowed laryngeal images to be dichotomized regardless of the condition of endoscopic examination. Endoscopic evaluation of laryngeal cartilage movement is subjective and is influenced by sedation with xylazine, evaluation through the alternate nostril, and different day of examination. The most consistent evaluation was obtained during repeated examination through the left nostril.     

Sedative effects of intramuscular administration of a low dose of romifidine in dogs

OBJECTIVE: To evaluate sedative effects of IM administration of a low dose of romifidine in dogs. ANIMALS: 13 healthy adult Beagles. PROCEDURE: Physiologic saline solution (0.2 ml), 0.1 % romifidine (10, 20, or 40 microg/kg), or 10% xylazine (1 mg/kg) was given IM in a crossover study design. Heart rate, respiratory rate, rectal temperature, hemoglobin saturation, and scores for sedation, muscle relaxation, posture, auditory response, and positioning response were recorded before and at regular intervals for up to 240 minutes after drug administration. RESULTS: Scores for sedation, muscle relaxation, posture, auditory response, and positioning response increased in a dose-dependent manner after romifidine administration. Sedation induced by the highest dose of romifidine (40 microg/kg) was comparable to that induced by xylazine (1 mg/kg). Heart rate, respiratory rate, and rectal temperature decreased in a dose-dependent manner after romifidine administration, but hemoglobin saturation did not change. CONCLUSIONS AND CLINICAL IMPLICATIONS: Romifidine (10, 20, or 40 microg/kg, IM) is an effective sedative in dogs, but causes a decrease in heart rate, respiratory rate, and rectal temperature.     

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.