Effects of intravenous xylazine hydrochloride on blood glucose, plasma insulin and rectal temperature in neonatal foals

The effects of intravenous xylazine hydrochloride on blood glucose, plasma insulin and rectal temperature were investigated in six foals at 10 and 28 days of age. These variables were also measured in three foals at 19 days of age when saline alone was injected. Rectal temperature fell significantly after 30 mins in both groups of xylazine treated foals and was still depressed after 120 mins. Hypothermia did not occur in the saline control group. There was no significant change in blood glucose or plasma insulin concentrations during the 120 mins following either xylazine or saline administration and no significant differences between the three groups of foals. When foals were allowed to suckle after being away from their dams for 2 h, there was a significant (P less than 0.01) rise in plasma insulin levels in all the groups. Blood glucose showed a concomitant rise but this was only significant in the saline group. Unlike adults, intravenous xylazine (1.1 mg/kg) does not produce hypoinsulinaemia and hyperglycaemia in foals. This study suggests that the inhibition of insulin release from pancreatic beta-cells by xylazine, which in adults is alpha 2-adrenoceptor mediated, is immature or absent in foals under one month of age.     

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.     

Caudal epidural analgesia induced by xylazine administration in cows

Xylazine (0.05 mg/kg of body weight diluted to a 5-ml volume, using 0.9% NaCl) or 5 ml of 0.9% NaCl was administered epidurally into the first caudal intervertebral space (Co1-Co2) in 8 cows (mean +/- SD body weight, 583 +/- 150 kg). Cows were observed for responses to deep needle pricking of the caudal dermatomes (S3 to Co), sedation, and ataxia. Heart rate, respiratory rate, body temperature, rate of ruminal contractions, coccygeal arterial blood pressure, pHa, blood gas tension (PaO2, PaCO2), base excess, total solids concentration, and PCV were determined before and after xylazine administration. Epidurally administered xylazine induced sedation and selective (S3 to Co) analgesia for at least 2 hours. Mild ataxia of hind limbs was observed in 6 cows, but all cows remained standing. Heart rate, respiratory rate, rate of ruminal contractions, arterial blood pressure, PaO2, PCV, and total solids concentration were significantly (P less than 0.05) decreased, and PaCO2, base excess, and bicarbonate concentration were significantly (P less than 0.05) increased after xylazine administration. Epidurally administered 0.9% NaCl did not alter sensory perception to needle pricking and did not affect any of the physiologic variables determined. Although epidural administration of xylazine induced analgesia and sedation in healthy cows, it should be avoided for epidural analgesia in cattle with heart disease, lung disease, and/or gastrointestinal disease because of its potent cardiopulmonary and ruminal depressant effects.     

Effect of xylazine on cerebrospinal fluid pressure in conscious horses.

Lumbosacral CSF pressure was measured in 6 horses via a catheter inserted through the lumbosacral space. Heart rate, facial artery pressure, central venous pressure, and CSF pressure were measured before IV injection of a saline solution control, for 15 minutes after saline solution injection, and for 60 minutes after the IV injection of 1.1 mg of xylazine/kg of body weight. Arterial pH and blood gases were analyzed before saline solution injection, 15 minutes after saline solution injection, and at 15, 30, and 60 minutes after xylazine injection. Constant craniocervical posture was maintained during sedation. Lumbosacral CSF pressure was significantly decreased for 15 minutes after xylazine injection. Diastolic arterial pressure was significantly increased 4 minutes after xylazine administration and diastolic and mean arterial pressure were increased at 6 and 8 minutes after xylazine administration. Small increases in systolic arterial blood pressure and central venous pressure, and a small decrease in heart rate were observed. There were no significant differences in the arterial blood gas values. It was concluded that IV injection of xylazine causes a decrease in intracranial pressure in healthy conscious horses. The effects may be different in horses with neurologic disease or cerebral trauma.     

Respiratory studies in foals from birth to seven days old

Respiratory measurements and blood-gas and acid-base values are reported in nine term induced foals. Measurements were performed at 2, 15, 30 and 60 mins, 4, 12, 24 and 48 h, and four and seven days after birth. Minute respiratory volume was significantly lower at birth than values from 12 h old. Tidal volume peaked at 60 mins old, while respiration rate decreased significantly at 15 mins after birth. Oxygen consumption was high at birth and decreased to its lowest values at 24 and 48 h. The respiratory exchange ratio and ventilatory equivalent showed few significant changes to seven days, as did the minute alveolar ventilation and physiological deadspace. The blood-gas and acid-base values indicated that the foals rapidly establish adequate pulmonary ventilation within minutes of birth, and that those values changed little from 12 h to seven days after birth. Body position had a significant effect on arterial oxygen tension with Pao₂ values in lateral recumbency being, on average, 14 mmHg lower than when the foals were standing.     

Behavioral and Cardiopulmonary Effects of a Constant Rate Infusion of Remifentanil–Xylazine for Sedation in Horses

Xylazine and remifentanil in constant rate infusion (CRI) could be used for sedation in horses without adverse effects. The objective was to evaluate behavioral and cardiopulmonary effects of an intravenous (IV) infusion of xylazine and remifentanil for sedation in horses. Xylazine (0.8 mg/kg IV) followed after 3 minutes by a CRI of xylazine and remifentanil (0.65 mg/kg/h and 6 μg/kg/h, respectively) was administered in 10 healthy horses for 60 minutes. Sedation, ataxia, and cardiopulmonary, hematological, and blood gases variables were evaluated. Heart rate decreased significantly during the first 25 minutes after CRI of xylazine and remifentanil, whereas the respiratory rate showed a significant decrease at 20 minutes and remained significantly low until the endpoint. There were no statistically significant fluctuations in blood arterial pressure, blood pH, partial pressure of arterial carbon dioxide, lactate, creatinine, calcium, chlorine, and sodium, compared with baseline values. Blood partial pressure of arterial oxygen and bicarbonate values were significantly higher compared with baseline values, whereas potassium decreased. Sedation and ataxia developed immediately after the administration of xylazine in all horses. All horses recovered successfully within 10 minutes after interruption of the CRI of xylazine and remifentanil, with no ataxia. No adverse effects were observed. The use of a combination of xylazine and remifentanil as sedation protocol has no adverse effects at the described dosage.     

Decreased sedation by xylazine and high blood pressure in cows with BSE.

Fifteen cows with bovine spongiform encephalopathy (BSE) and 90 healthy cows were given xylazine intramuscularly at a dosage of 0.15 mg/kg bodyweight. The onset of sedation and of drooling was recorded, and the heart and respiratory rates and the systolic and diastolic blood pressure were measured every five minutes for 40 minutes. All the healthy cows but only five of the 15 cows with BSE became sedated, and the period between the administration of xylazine and the onset of sedation was twice as long in the cows with BSE than in the healthy cows (15.0 [7.5] and 7.6 [2.6] minutes). Throughout the observation period, the blood pressure of the cows with BSE was significantly higher than that of the healthy cows, and the blood pressure of the healthy cows, but not of the cows with BSE, decreased significantly towards the end of the observation period.     

Effects of changing body position on oxygenation and arterial blood pressures in foals anesthetized with guaifenesin, ketamine, and xylazine

ObjectiveTo investigate the impact of a change in body position on blood gases and arterial blood pressures in foals anesthetized with guaifenesin, ketamine, and xylazine.Study designProspective, randomized experimental study.AnimalsTwelve Quarter Horse foals, age of 5.4 ±0.9 months and weighing 222 ± 48 kg.MethodsFoals were anesthetized with guaifenesin, ketamine, and xylazine for 40 minutes in lateral recumbency and then assigned to a change in lateral recumbency after hoisting (Group 1, n = 6), or no change (Group 2, n = 6). Oxygen 15 L minute^?1 was insufflated into the endotracheal tube throughout anesthesia. Arterial blood pressure, heart rate, respiratory rate (f_R), inspired fraction of oxygen (FiO₂), and end-tidal carbon dioxide (Pe’CO₂) were measured every 5 minutes. Arterial pH and blood gases [arterial partial pressure of oxygen (PaO₂), arterial partial pressure of carbon dioxide (PaCO₂)] were measured at 10, 30, and 40 minutes after induction, and 5 minutes after hoisting. Alveolar dead space ventilation and PaO₂/FiO₂ were calculated. Two repeated measures models were used. All hypothesis tests were two-sided and significance level was α = 0.05. All values are presented as least square means ± SE.ResultsValues at time-matched points from the two groups were not significantly different so they were combined. Arterial partial pressure of oxygen decreased significantly from 149 ± 14.4 mmHg before hoisting to 92 ± 11.6 mmHg after hoisting (p=0.0013). The PaO₂/FiO₂ ratio decreased from 275 ± 30 to 175 ± 24 (p=0.0055). End-tidal carbon dioxide decreased significantly from 48.7 ± 1.6 to 44.5 ± 1.2 mmHg (p=0.021). Arterial partial pressure of carbon dioxide, blood pressures and heart rates measured 5 minutes after hoisting were not different from measurements obtained before hoisting.Conclusion and clinical relevanceHoisting decreased PaO₂ in anesthetized healthy foals. Administration of supplemental oxygen is recommended to counter the decrease in oxygenation and PaO₂ measurement is necessary to detect early changes.     

Cardiovascular and pulmonary effects of recumbency in two conscious ponies

Respiratory dead-space, tidal volume, respiratory rate, blood gases, cardiac output, heart rate and arterial and pulmonary arterial blood pressures were measured in two conscious, trained ponies in the standing position and in left lateral recumbency. The ponies were reluctant to remain lying down for more than about 20 mins but the reason for this did not become apparent. Tidal volume was reduced during recumbency but the respiratory rate increased, tending to maintain the minute volume at about that of the standing animal. Arterial carbon dioxide tension did not change significantly from standing values but the mean arterial oxygen tension values tended to decrease in both ponies during recumbency because of a slight increase in pulmonary venous admixture. Venous admixture in these two laterally recumbent conscious animals was considerably less than previously reported for anaesthetised subjects.     

Cardiovascular and allied actions of xylazine and atropine in the unanaesthetized goat

The cardiovascular effects of xylazine and atropine, separately and in combination, were studied in goats. Methylatropine was used to distinguish between the central and peripheral effects of atropine. Mean arterial blood pressure and heart rate were recorded, and the sedative effect and changes in respiration and salivation noted. Intravenous infusion of xylazine (2.4-80.0 micrograms/kg) decreased mean arterial blood pressure and heart rate in a dose-dependent manner. Single intravenous injections of both atropine sulphate (0.1 mg/kg) and methylatropine bromide (0.05 mg/kg) increased blood pressure and heart rate. After methylatropine, tachycardia lasted twice as long as after atropine. Following atropinization, a potentiated rise in mean arterial blood pressure was present during the infusion of xylazine (80 micrograms/kg). Xylazine-induced bradycardia was reversed by both atropine and methylatropine. The action of atropine is presumed to be primarily peripheral because of the similar effects with methylatropine. Xylazine-induced sedation was dose dependent. At the highest dose the goats were unable to stand for 30-60 min, respiration became irregular with periods of apnoea, and saliva started to drip a few minutes after infusion without increased salivation. Atropine had no visible effect on the sedation, pattern of respiration or saliva dripping effect of xylazine.     

Influence of yohimbine and tolazoline on the cardiovascular, respiratory, and sedative effects of xylazine in the horse

To determine the effects of yohimbine and tolazoline on the cardiovascular, respiratory and sedative effects of xylazine, four horses were sedated with xylazine and treated with either yohimbine, tolazoline or saline. Xylazine was administered as an intravenous (i.v.) bolus (1.0 nig/kg) followed by a continuous infusion at the rate of 12 μg/kg/min. Heart rate, respiratory rate, mean arterial pressure, arterial blood gases, and the chin-to-floor distance were recorded throughout the experiment. After 60 min, either yohimbine or tolazoline was administered i.v. in incremental doses until reversal of sedation (defined as the return of the chin-to-floor distance to baseline values) was achieved. A control group in which a saline bolus was administered instead of an antagonist drug was included for comparison.
The average dose of yohimbine administered was 0.12 ± 0.02 (SEM) mg/kg. While the average dose of tolazoline was 7.5 ± 1.1 mg/kg. Both tolazoline and yohimbine antagonized the ventricular bradycardia and A-V conduction disturbances observed with xylazine administration. No change in mean arterial pressure was observed with xylazine or yohimbine administration, but tolazoline caused persistent mild systemic hypertension. There were no clinically significant changes in respiratory rate or arterial blood gas values with administration of either xylazine, yohimbine or tolazoline. The chin-to-floor distance decreased significantly with xylazine administration and increased significantly with administration of either yohimbine or tolazoline. In conclusion, both yohimbine and tolazoline successfully antagonized the cardiovascular and CNS depression associated with xylazine administration.     

Preliminary Results of Behavioral and Cardiopulmonary Effects of a Constant Rate Infusion of Remifentanil–Xylazine for Sedation in Horses

Standing surgical procedures are performed commonly in horses under sedation. The use of a xylazine and remifentanil combination has not been investigated in horses. We proposed to evaluate behavioral and cardiopulmonary effects of an intravenous (IV) infusion of xylazine with remifentanil for sedation in horses. Xylazine (0.8 mg/kg IV) followed in 3 minutes by remifentanil (0.0005 mg/kg IV), and a constant rate infusion of xylazine and remifentanil (0.65 mg/kg/h; 0.0225 mg/kg/h, respectively) was administered in three horses. Heart rate, respiratory rate (RR), arterial blood pressures, quality of sedation, pH, partial pressure of arterial CO₂ (PaCO₂), partial pressure of arterial O₂ (PaO₂), ataxia, sedation, and sedation overall outcome were assessed. Heart rate and RR remained within normal values during sedation without significant changes from baseline. Systolic, mean, and diastolic arterial blood pressures were increased during sedation. There were no significant changes in pH, PaCO₂, and PaO₂. Sedation developed immediately after injection of xylazine in the three horses but did not increase after remifentanil bolus or IV infusion of both drugs. None of the mares had ataxia. Adverse effects during and after sedation were present: excitement, increase in locomotor activity, and decrease in the gastrointestinal motility. The combination of xylazine and remifentanil sedation protocol produces adverse effects. This protocol cannot be recommended for clinical conditions, at the described doses.     

Effects of atipamezole on xylazine sedation in ponies.

Atipamezole antagonism of xylazine sedation was evaluated in six ponies. Atipamezole (0.15 mg/kg) or saline was injected intravenously 15 minutes after the ponies had been sedated with xylazine (1.0 mg/kg). Arterial blood pressure and gases, pulse and respiratory rates, the electrocardiogram, nose-to-ground distance and a subjective sedation score were recorded. The pretreatment nose-to-ground distance and PaO2 returned to normal sooner after atipamezole than after saline and the ponies' appetite and normal locomotion also recovered sooner. No significant differences were observed between the effects of saline and atipamezole on the other measurements.     

Stress responses in ponies during halothane or isoflurane anaesthesia after induction with thiopentone or xylazine/ketamine

Endocrine and metabolic responses to anaesthesia with three different anaesthetic regimes were examined in six ponies. All animals were anaesthetised with each protocol: acepromazine-thiopentone-isoflurane, xylazine-ketamine- halothane and xylazine-ketamine-isoflurane. Anaesthesia was maintained for 2 h. Pulse rate, respiratory rate, arterial blood pressure, arterial blood gases and pharyngeal and skin temperature were measured and blood was withdrawn for glucose, lactate, cortisol, insulin, liver and muscle enzymes and total protein assay. Measurements were made before anaesthesia, at 20 min intervals during anaesthesia and at 20 mins and 2, 4, 6 and 24 h after anaesthesia. The effects of anaesthesia were similar in all groups. Arterial blood pressure decreased and oxygen tension and plasma cortisol concentration increased in all groups. Arterial carbon dioxide tension increased and respiratory rate and pH decreased in all ponies anaesthetised with isoflurane. There was a tendency for increased glucose and lactate concentrations and decreased insulin concentration and packed cell volume, particularly in the xylazine-ketamine groups. There was no change in pulse rate except for a transient increase at induction with thiopentone. The results were compared with data reported by Taylor (1989), which were collected from the same animals during acepromazine-thiopentone-halothane anaesthesia, and were found to be similar. It was concluded that these commonly used anaesthetic protocols themselves constitute a considerable insult or stressor in horses. However, the stress response to all the regimes investigated was similar and the precise stimulus to this response has yet to be elucidated.     

Effects of xylazine on ventilation in horses.

The effects of 3 commonly used dosages (0.3, 0.5, and 1.1 mg/kg of body weight, IV) of xylazine on ventilatory function were evaluated in 6 Thoroughbred geldings. Altered respiratory patterns developed with all doses of xylazine, and horses had apneic periods lasting 7 to 70 seconds at the 1.1 mg/kg dosage. Respiratory rate, minute volume, and partial pressure of oxygen in arterial blood (PaO2) decreased significantly (P less than 0.001) with time after administration of xylazine, but significant differences were not detected among dosages. After an initial insignificant decrease at 1 minute after injection, tidal volume progressively increased and at 5 minutes after injection, tidal volume was significantly (P less than 0.01) greater than values obtained before injection. Partial pressure of carbon dioxide in arterial blood (PaCO2) was insignificantly increased. After administration of xylazine at a dosage of 1.1 mg/kg, the mean maximal decrease in PaO2 was 28.2 +/- 8.7 mm of Hg and 22.2 +/- 4.9 mm of Hg, measured with and without a respiratory mask, respectively. Similarly, the mean maximal increase in PaCO2 was 4.5 +/- 2.3 mm of Hg and 4.2 +/- 2.4 mm of Hg, measured with and without the respiratory mask, respectively. Significant interaction between use of mask and time was not detected, although the changes in PaO2 were slightly attenuated when horses were not masked. The temporal effects of xylazine on ventilatory function in horses should be considered in selecting a sedative when ventilation is inadequate or when pulmonary function testing is to be performed.     

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.     

Influence of age on neutrophil function in foals.

Functional activities (phagocytosis and killing) of neutrophil leucocytes (NL) and immunoglobulin G concentrations were evaluated in six healthy foals from birth to 6 months of age. Peripheral blood NL were reacted with Streptococcus equisimilis in 20 per cent pooled equine serum for 30, 60 and 90 mins and functional activities of NL were determined using a fluorochrome microassay. Values for foal NL function were compared with those of healthy adult horses (n = 28). Foal neutrophil function was influenced by age. Killing capacity of NL decreased, whereas phagocytic capacity increased, until 113 days of age, after which a reversal in trends became apparent. Immunoglobulin G concentrations changed significantly over time and were lowest at 29 to 56 days of age. All foal values for NL function fell within the range of normal values established for healthy adult horses.     

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.     

Cardiovascular effects of xylazine and detomidine in horses

The cardiovascular effects of xylazine and detomidine in horses were studied. Six horses were given each of the following 5 treatments, at 1-week intervals: xylazine, 1.1 mg/kg, IV; xylazine, 2.2 mg/kg, IM; detomidine, 0.01 mg/kg, IV; detomidine, 0.02 mg/kg, IV; and detomidine, 0.04 mg/kg, IM. All treatments resulted in significantly decreased heart rate, increased incidence of atrioventricular block, and decreased cardiac output and cardiac index; cardiac output and cardiac index were lowest following IV administration of 0.02 mg of detomidine/kg. Mean arterial pressure was significantly reduced for various periods with all treatments; however, IV administration of 0.02 mg of detomidine/kg caused hypertension initially. Systemic vascular resistance was increased by all treatments. Indices of ventricular contractility and relaxation, +dP/dt and -dP/dt, were significantly depressed by all treatments. Significant changes were not detected in stroke volume or ejection fraction. The PCV was significantly reduced by all treatments. Respiratory rate was significantly decreased with all treatments, but arterial carbon dioxide tension did not change. Arterial oxygen tension was significantly decreased briefly with the 3 IV treatments only.     

The Effect of Sedation on Gastric Emptying of a Liquid Marker in Ponies

OBJECTIVE: The effect of sedation on gastric emptying was evaluated in six ponies by monitoring serum concentrations of acetaminophen (AP) after intragastric administration. EXPERIMENTAL DESIGN: Prospective randomized experimental study. ANIMALS: Six adult ponies, 135 to 275 kg. METHODS: Fifteen minutes after the intravenous administration of xylazine (1 mg/kg), butorphanol (0.05 mg/kg), acepromazine (0.05 mg/kg) or saline, ponies were given AP (20 mg/kg in 350 mL water) by stomach tube. Blood for AP analysis was collected at baseline and 15, 30, 45, 75, 90, 105, and 120 minutes after AP administration. The time (Tmax) to reach peak serum concentration (Cmax), and the area under the AP serum concentration versus time curve (AUC) were determined for each treatment group. RESULTS: Tmax was 31 mins in the control group, and this increased significantly (P<.05) after sedation. Cmax decreased (P<.05) after xylazine administration, and AUC decreased (P<.05) after acepromazine. CONCLUSIONS: This study indicated that sedation has a significant effect on the gastric emptying rate of a liquid in ponies.