Pharmacokinetics and sedative effects of intramuscular medetomidine in domestic sheep

The effects of repeated doses of xylazine-ketamine and medetomidineketamine anesthesia on DNA damage in the liver and kidney

PURPOSE

This study evaluated the DNA damage caused by repeated doses of xylazine-ketamine and medetomidine-ketamine anesthesia in the liver and kidneys.

METHODS

In this study, 60 rats were used. The rats were divided into group 1 (xylazine-ketamine), and group 2 (medetomidine-ketamine), and these anesthetic combinations were administered to the rats at repeated doses with 30-min intervals. The effects of these anesthetic agents on the tumor necrosis factor-alpha gene for DNA damage were investigated.

RESULTS

According to the gene expression results, it was observed that a single dose of xylazine-ketamine was 2.9-fold expressed, while first and second repeat doses did not show significant changes in expression levels. However, in the case of the third repetition, it was observed to be 3.8-fold overexpressed. In the case of medetomidine-ketamine administration, it was observed that a single-dose application resulted in a 1.04-fold expression, while the first and the third repeat doses showed a significant down expression. The samples from the second repeat dose administration group were found to have insignificant levels of expression.

CONCLUSIONS

This study can contribute to understanding the safe anesthetic combination in research and operations in which xylazine-ketamine and medetomidine-ketamine combinations are used.

Cardiorespiratory effects of isoflurane and medetomidine-tiletamine-zolazepam in 12 bonobos (Pan paniscus)

BACKGROUND

Cardiovascular disease is a significant cause of mortality in captive great apes. However, data from bonobos are lacking due to a paucity of collections in Europe. Comprehensive preventive screening is required to understand the aetiopathogenesis of cardiovascular disease, but the provision of a stable and predictable anaesthetic protocol with minimal cardiovascular effects is challenging.

METHODS

This prospective, observational case series reports anaesthesia of 12 bonobos using hand-injected medetomidine and tiletamine-zolazepam followed by maintenance with isoflurane in oxygen. Comprehensive clinical examinations, including arterial blood gases and echocardiography were undertaken.

RESULTS

Induction of anaesthesia with hand injection was successful in all but one individual. Respiratory acidosis with metabolic alkalosis and respiratory alkalosis with metabolic acidosis were documented. Hypochloraemia may have contributed to non-respiratory alkalosis in one individual. Ten bonobos experienced hypotension and required haemodynamic support. Both N-terminal pro b-type natriuretic peptide and troponin I cardiac biomarkers correlated with left ventricular ejection fraction (percentage). Recovery was smooth, rapid and uneventful in all animals.

LIMITATIONS

The effects of the anaesthetic must be considered during echocardiographical interpretation.

CONCLUSIONS

The anaesthesia protocol provided a safe, predictable induction and recovery, facilitating diagnostics (including echocardiography) and minor surgical procedures. Comprehensive monitoring, including invasive blood pressure monitoring and haemodynamic support, is highly recommended.

Comparing the effects of intravenous injection and intranasal atomisation of detomidine in sheep

BACKGROUND

Detomidine is an α-2 agonist sedative drug which reduces the release of norepinephrine in nerves. Administering this drug through intranasal (IN) route could cause direct transmission to the central nervous system. Therefore, IN administration of detomidine would decrease the side effects and the onset of sedation.

OBJECTIVES

In this study, IN administration of detomidine in sheep through an atomiser was compared to its IV administration.

METHODS

Fifteen mature female sheep with an approximate weight of 49.53 ± 1.72 kg were used. They were randomly divided into three groups: (1) atomising 10 μg/kg (IND₁₀ ); (2) IV 10 μg/kg (IVD) and (3) atomising 30 μg/kg (IND₃₀ ). Following administration, vital signs, electrocardiographic components, sedative score and biochemistry profile were measured after 15, 30 and 60 min, which were compared with the baseline measures.

RESULTS

Bradycardia and the percentage of reduction from the baseline value in the respiratory rate were lower in the IND₁₀ group compared to those in the IVD group. There was no significant difference in terms of the temperature and blood oxygen saturation (SpO₂ ) among all the groups (p > 0.05). The level of cortisol declined in all the groups, and in the IND₃₀ (60 min), it was significantly different with the baseline value. The level of glucose increased in all the groups compared to the baseline, which was not significant. Insulin concentration was reduced in all the groups, and in the IND₃₀ group, it changed significantly 60 min after the drug administration. Sedation onset time was faster in the IV group. However, sedation scores between the two administration methods were not different, and only a dose-dependent increase was found in the sedation score in the atomisation group.

CONCLUSIONS

Our findings revealed that IN atomisation of detomidine triggers similar sedation as its IV administration, which could be used as an alternative method.

Comparative evaluation of the sedative and physiological effects of medetomidine alone and in combination with pethidine, morphine, tramadol, and methadone in goats

Background

The use of combinations of α₂‐adrenergic agonists and opioids has been published as providing superior sedation than either drug alone.

Introduction

The present study aims to compare the sedative and physiological effects of intravenous (IV) administration of medetomidine alone and in combination with methadone, morphine, tramadol, and pethidine in goats.

Methods

Ten healthy goats aged 12 ± 3 months and weight of 22 ± 4 kg were used in an experimental, crossover (Latin square), randomized, and blinded study. The animals were assigned to five IV treatments with a minimum washout period of 8 days between treatments: medetomidine (20 μg kg⁻¹), medetomidine/methadone (0.5 mg kg⁻¹), medetomidine/morphine (0.5 mg kg⁻¹), medetomidine/tramadol (5 mg kg⁻¹), and medetomidine/pethidine (1 mg kg⁻¹).

Results

Clinical adverse effects such as tremors (facial and generalized), bruxism, nystagmus, mydriasis, and vocalization were presented in all the medetomidine/opioid treatments. Clinical adverse effects were observed at 10–90 minutes in medetomidine/opioid treatments. Animals in all treatments were sedated at 5–90 minutes. Sedation was significantly higher in medetomidine/opioid treatments than in medetomidine at 15–30 minutes after administration (P < 0.05). In all treatments, heart rate and respiratory rate significantly decreased from baseline at 5–105 and 30–60 minutes, respectively. There was no significant difference in heart and respiratory rates between different treatments at any time point. Ruminal motility was decreased in medetomidine and medetomidine/opioid treatments at 10–75 and 10–105 minutes, respectively. Compared with medetomidine, ruminal motility was significantly lower in medetomidine/opioid treatments at 75–105 minutes.

Conclusion

The use of combinations of medetomidine/opioids would be considered for superior sedation at 15–30 minutes after administration in goats. No significant differences were detected among opioids in combination with medetomidine in goats.

The use of combinations of medetomidine/opioids would be considered for superior sedation at 1530 minutes after administration in goats. No significant differences were detected among opioids in combination with medetomidine in goat.

Evaluation of the sedative and physiological effects of xylazine, detomidine, medetomidine and dexmedetomidine in goats

Background

Many α₂‐agonists are commonly used for sedation and analgesia in ruminants.

Introduction

The present study aims to compare the sedative and physiological effects of intravenous (IV) administration of xylazine, detomidine, medetomidine and dexmedetomidine in goats.

Methods

Ten healthy goats aged 6 ± 1 months and weighing 15 ± 2 kg were used in experimental, crossover Latin square, randomised and blinded study. Animals were assigned to five IV treatments: control (normal saline); xylazine (100 μg kg⁻¹); detomidine (50 μg kg⁻¹); medetomidine (20 μg kg⁻¹) and dexmedetomidine (5 μg kg⁻¹). The degree of sedation was investigated using a numerical ranking scale of 0–10. Sedation scores were compared at each time using nonparametric (Kruskal–Wallis and Mann–Whitney U) tests.

Results

Heart rate (HR), respiratory rate (RR), rectal temperature (RT), ruminal motility and capillary refill time (CRT) were performed before (baseline) and after drug administration. Animals in α₂‐adrenergic agonist treatments were sedated at 5–60 min. There were no significant differences among α₂‐adrenergic agonist treatments at 5–60 min in sedation scores. HR significantly decreased from baseline 5–90 min after α₂‐adrenergic agonists’ administration. Ruminal motility was decreased in α₂‐adrenergic agonist treatments at 5, 90 and 120 min and absent at 10–60 min. A significant decrease from baseline in RR was detected between 30 and 90 min after α₂‐adrenergic agonists’ administration. RT was unchanged in any treatment for 120 min. CRT was less than 2 s at all time points following each treatment.

Conclusions

The duration of sedation was up to 60 min after IV administration of xylazine (100 μg kg⁻¹), detomidine (50 μg kg⁻¹), medetomidine (20 μg kg⁻¹) and dexmedetomidine (5 μg kg⁻¹) in goats in this study. No significant differences were detected between xylazine, detomidine, medetomidine and dexmedetomidine in goats.

The duration of sedation was up to 60 minutes after IV administration of xylazine (100 μg kg⁻¹), detomidine (50 μg kg⁻¹), medetomidine (20 μg kg⁻¹) and dexmedetomidine (5 μg kg⁻¹) in goats. No significant differences were detected between xylazine, detomidine, medetomidine and dexmedetomidine in goats.

Concentrations of vatinoxan and xylazine in plasma, cerebrospinal fluid and brain tissue following intravenous administration in sheep

OBJECTIVES

To investigate the extent of vatinoxan distribution into sheep brain, and whether vatinoxan influences brain concentrations of xylazine; and to examine the utility of cerebrospinal fluid (CSF) as a surrogate of brain tissue concentrations for vatinoxan and xylazine.

STUDY DESIGN

Randomised, blinded, experimental study.

ANIMALS

A total of 14 adult female sheep.

METHODS

Sheep were randomly allocated into two equal groups and premedicated with either intravenous (IV) vatinoxan (750 μg kg^-1, VX) or saline (SX) administered 10 minutes before IV xylazine (500 μg kg^-1). Sedation was subjectively assessed at selected intervals before and after treatments. At 10 minutes after xylazine administration, a venous blood sample was collected and the sheep were immediately euthanised with IV pentobarbital (100 mg kg^-1). Plasma, CSF and brain tissues were harvested, and concentrations of vatinoxan and xylazine were quantified using liquid chromatography-tandem mass spectrometry. Drug ratios were then calculated and the data were analysed as appropriate.

RESULTS

The brain-to-plasma and CSF-to-plasma ratios of vatinoxan were 0.06 ± 0.013 and 0.05 ± 0.01 (mean ± standard deviation), respectively. Xylazine brain concentrations were not significantly different (835 ± 262 versus 1029 ± 297 ng g^-1 in groups VX and SX, respectively) and were approximately 15-fold higher than those in plasma. The CSF-to-brain ratio of vatinoxan was 0.8 ± 0.2, whereas xylazine concentrations in the brain were approximately 17-fold greater than those in CSF, with and without vatinoxan.

CONCLUSIONS AND CLINICAL RELEVANCE

Vatinoxan did not significantly affect sedation with xylazine or the concentrations of xylazine in the brain. CSF is not a good predictor of xylazine concentrations in the brain, whereas vatinoxan concentrations were concordant between the brain and CSF, using the dosages in this study.

Evaluation of the Novel PET Tracer [11C]HACH242 for Imaging the GluN2B NMDA Receptor in Non-Human Primates

PURPOSE

There are currently no positron emission tomography (PET) radiotracers for the GluN2B (NR2B) binding sites of brain N-methyl-D-aspartate (NMDA) receptors. In rats, the GluN2B antagonist Ro25-6981 reduced the binding of N-((5-(4-fluoro-2-[¹¹C]methoxyphenyl)pyridin-3-yl)methyl)cyclopentanamin ([¹¹C]HACH242). This paper reports the evaluation of [¹¹C]HACH242 PET in non-human primates at baseline and following administration of the GluN2B negative allosteric modulator radiprodil.

PROCEDURES

Eight 90-min dynamic [¹¹C]HACH242 PET scans were acquired in three male anaesthetised rhesus monkeys, including a retest session of subject 1, at baseline and 10 min after intravenous 10 mg/kg radiprodil. Standardised uptake values (SUV) were calculated for 9 brain regions. Arterial blood samples were taken at six timepoints to characterise pharmacokinetics in blood and plasma. Reliable input functions for kinetic modelling could not be generated due to variability in the whole-blood radioactivity measurements.

RESULTS

[¹¹C]HACH242 entered the brain and displayed fairly uniform uptake. The mean (± standard deviation, SD) T_max was 17 ± 7 min in baseline scans and 24 ± 15 min in radiprodil scans. The rate of radioligand metabolism in plasma (primarily to polar metabolites) was high, with mean parent fractions of 26 ± 10 % at 20 min and 8 ± 5 % at 85 min. Radiprodil increased [¹¹C]HACH242 whole-brain SUV in the last PET frame by 25 %, 1 %, 3 and 17 % for subjects 1, 2, 3 and retest of subject 1, respectively. The mean brain to plasma ratio was 5.4 ± 2.6, and increased by 39 to 110 % in the radiprodil condition, partly due to lower parent plasma radioactivity of -11 to -56 %.

CONCLUSIONS

The present results show that [¹¹C]HACH242 has a suitable kinetic profile in the brain and low accumulation of lipophilic radiometabolites. Radiprodil did not consistently change [¹¹C]HACH242 brain uptake. These findings may be explained by variations in cerebral blood flow, a low fraction of specifically bound tracer, or interactions with endogenous NMDA receptor ligands at the binding site. Further experiments of ligand interactions are necessary to facilitate the development of radiotracers for in vivo imaging of the ionotropic NMDA receptor.

Comparative evaluation of electrocardiographic effects of different doses of medetomidine and xylazine in calf-camels (Camelus dromedarius)

This experimental, prospective, randomised, and blinded study aimed to perform comparative evaluation of electrocardiographic (ECG) effects of different doses xylazine and medetomidine in dromedary calves after intravenous (IV) administration. A total of twenty five clinically and paraclinically healthy male dromedary calves aged 15±2 weeks and weighing 95±5.5 kg were assigned randomly to five different groups (four experimental and one control). Groups XL and XH received a low (0.2 mg kg-1) and high (0.4 mg kg-1) dose of xylazine hydrochloride and groups ML and MH received a low (10 µg kg-1) and high (20 µg kg-1) dose of medetomidine hydrochloride once, IV. Finally, the control group (C) received normal saline in the same manner. ECG indices were evaluated on post treatment 0, 5, 10, 15, 30, 60, 90, 120 min, and 24 h. There was no significant difference in heart rate (HR) in all experimental groups at T90. HR was significantly lower after high doses than after low doses of medetomidine and xylazine at T120. HR was significantly lower in XH than in other groups of study at T24. At T90 QRS amplitude in XH was statistically lower than in control and XL groups. Analysis of P wave duration revealed that in MH and XH it was significantly longer than in ML, XL and control at T5. Duration of P wave in control group was significantly shorter than in all experimental groups from T10 to T90. RR interval duration was significantly shorter at T5 and T10 in control group compared to experimental groups. At T120, RR interval duration in MH and XH was considerably longer than that in ML, XL, and control. Compared with control group, cardiac arrhythmia scores were significantly lower than in all experimental groups from T5 to T60. At T90 and T120 in MH and XH, cardiac arrhythmia scores were significantly higher than those of XL, ML, and control. According to our findings, using low dose of medetomidine (10 µg kg-1) and xylazine (0.2 mg kg-1) was suggested in comparison with high dose of medetomidine (20 µg kg-1) and xylazine (0.4 mg kg-1) in dromedary calves with cardiac diseases in the field.

Sedative and cardiorespiratory effects of detomidine constant rate infusion in sheep

The use of sheep in experiments is widespread and is increasing worldwide, and so is the need to develop species-specific anaesthetic techniques to ensure animal safety. Previous studies have mentioned several protocols involving the administration of alpha-2 adrenergic agonists in sheep; however, assessment of the efficacy and safety of these infusion techniques is still relatively new. Thus, the aim of the present study is to assess the effectiveness of detomidine constant rate infusion (CRI) in sheep by measuring the cardiovascular and respiratory parameters, blood gas variables and sedation scores. Eight adult female Santa Inês sheep received 20 µg/kg of detomidine hydrochloride intravenously as a bolus loading dose, followed by an infusion rate of 60 µg/kg/h. The heart rates and respiratory rates changed continuously during the CRI period. No arrhythmias were observed. The reduction in arterial partial pressure of oxygen (PaO₂) was not significant, but one animal showed signs of hypoxaemia (minimum PaO₂ of 66.9 mmHg). The arterial partial pressure of carbon dioxide (PaCO₂) increased, but the animals did not become hypercapnic. The bicarbonate (HCO^3-), pH and base excess (BE) tended towards metabolic alkalosis. The cardiac output (CO), stroke volume (SV), cardiac index (CI) and ejection fraction (EF%) showed no significant changes. The fractional shortening (FS%) decreased slightly, starting at T_45min. Sedation scores varied between 3 (0/10) after sedation and during recovery and 7 (0/10) during CRI. We concluded that administering detomidine at an infusion rate of 60 µg/kg/h in Santa Inês sheep is a simple technique that produces satisfactory sedation for minimally invasive procedures.

The Effect of Acepromazine Alone or in Combination with Methadone, Morphine, or Tramadol on Sedation and Selected Cardiopulmonary Variables in Sheep

The sedative and selected cardiopulmonary effects of acepromazine alone or in combination with methadone, morphine, or tramadol were compared in sheep. Six ewes were randomly assigned to treatments: A (0.05 mg/kg acepromazine), AM (A plus 0.5 mg/kg methadone), AMO (A plus 0.5 mg/kg morphine), and AT (A plus 5 mg/kg tramadol). Parameters were assessed before sedative drug administration (baseline) and every 15 minutes thereafter, for two hours. Treatments A and AM were associated with increases in sedation score for 60 minutes and treatments AMO and AT for 30 minutes; however, there were no significant differences between treatments. There was a decrease in mean arterial pressure compared to baseline values in treatment A at 15, 45, 60, and 90 minutes, in treatment AM at 15 minutes, and in treatment AT from 45 to 120 minutes. Arterial blood carbon dioxide pressure increased at all time points in all treatments. Arterial oxygen pressure decreased in treatment AMO at 15, 30, and 120 minutes and in treatment AT at 15–45, 105, and 120 minutes, compared to baseline. Acepromazine alone causes a level of sedation similar to that observed when it is coadministered with opioids methadone, morphine, and tramadol. These combinations did not cause clinical cardiopulmonary changes.

Intraperitoneal medetomidine: A novel analgesic strategy for postoperative pain management in pregnant sheep

The absorption of medetomidine released by continuous infusion from an osmotic pump in the abdominal cavity was studied in pregnant sheep during the 24 h postoperative period. Additionally pain and sedation was assessed. Eleven sheep were studied: six were treated with a medetomidine loaded osmotic pump delivering 10 μL/h (3 μg/kg/h medetomidine); and five with a saline loaded osmotic pump (control). Serial blood samples were taken and analysed to determine plasma medetomidine levels. Medetomidine was absorbed from the peritoneal cavity and a steady plasma concentration was achieved within 10 h, mean (SD) peak concentration was 2.87 (0.22) ng/mL. Sheep receiving medetomidine analgesia had significantly lower pain scores at 10 h than controls. Four control sheep required rescue analgesia, compared with 0 in the treatment group. Delivery of 3 μg/kg/h medetomidine by an intraperitoneal osmotic pump to pregnant sheep in the 24 h postoperative period provides adequate plasma concentrations of medetomidine for analgesia without sedation.

Transplacental transfer of medetomidine and ketamine in pregnant ewes

The extent of placental transfer of medetomidine and ketamine is unknown in pregnant ewes. Date-mated singleton (n = 8) and twin (n = 8) pregnant merino cross ewes were anaesthetized for Caesarean delivery of preterm lamb fetuses. A combination of medetomidine (20 μg/kg) and ketamine (10 mg/kg) was administered by intravenous injection and surgery performed immediately thereafter. Blood samples were collected from the ewe at one, five and 10 min after intravenous injection and from the umbilical vein of the fetus at delivery. Non-pregnant ewes were also anaesthetized (n = 8). There was no difference in the plasma concentration of medetomidine or ketamine when comparing singleton and twin ewes or pregnant and non-pregnant ewes for the short duration of the study. Fetal plasma concentrations of each drug were comparable to the maternal concentrations at the same time. We conclude that both drugs cross the placenta readily and provide anaesthesia and analgesia for the fetus when it is delivered.

A 2 -agonists in sheep: a review

OBJECTIVE

To review the use and adverse effects of alpha(2)-agonists in sheep.

STUDY DESIGN

Literature review.

MATERIAL AND METHODS

'Pubmed' of the United States National Library of Medicine and 'Veterinary Science' of CAB International were searched for references relating sheep to alpha(2)-agonists. The bibliographies of retrieved articles were further scrutinized for pertinent references, and relevant articles were selected manually.

RESULTS

Reports on the use of clonidine, xylazine, detomidine, romifidine, medetomidine and dexmedetomidine, MPV-2426 and ST-91 in sheep were found in the literature. Most of the studies described xylazine followed by medetomidine and clonidine. The literature on detomidine and romifidine in sheep was sparse. Reports included pharmacokinetic studies, evaluation of sedative, analgesic, and anaesthetic techniques with or without cardiovascular effects, and experimental investigations of adverse effects (mainly hypoxaemia) including the mechanisms of pulmonary oedema and impaired oxygenation after alpha(2)-agonist administration.

CONCLUSIONS

A(2)-agonists are potent and effective analgesics in sheep. In combination with ketamine, they are frequently used for the induction and maintenance of anaesthesia, in this case analgesia is satisfactory. The degree of hypoxaemia which occurs with all commercially available alpha(2)-agonists is highly variable and depends on individual or breed-related factors; the most severe reactions occur after intravenous (IV) injection and during general anaesthesia. Clinical relevance Subclinical respiratory disease is common in sheep. Rapid IV injection of alpha(2)-agonists without supplementary oxygen should be avoided whenever hypoxaemia may be critical.

Comparison of two pre-anaesthetic medetomidine doses in isoflurane anaesthetized sheep

OBJECTIVE

To compare the sedative, anaesthetic-sparing and arterial blood-gas effects of two medetomidine (MED) doses used as pre-anaesthetic medication in sheep undergoing experimental orthopaedic surgery.

STUDY DESIGN

Randomized, prospective, controlled experimental trial.

ANIMALS

Twenty-four adult, non-pregnant, female sheep of various breeds, weighing 53.9 +/- 7.3 kg (mean +/- SD).

METHODS

All animals underwent experimental tibial osteotomy. Group 0 (n = 8) received 0.9% NaCl, group L (low dose) (n = 8) received 5 microg kg(-1) MED and group H (high dose) (n = 8) received 10 microg kg(-1) MED by intramuscular (IM) injection 30 minutes before induction of anaesthesia with intravenous (IV) propofol 1% and maintenance with isoflurane delivered in oxygen. The propofol doses required for induction and endtidal isoflurane concentrations (F(E')ISO) required to maintain anaesthesia were recorded. Heart and respiratory rates and rectal temperature were determined before and 30 minutes after administration of the test substance. The degree of sedation before induction of anaesthesia was assessed using a numerical rating scale. Arterial blood pressure, heart rate, respiratory rate, FE'ISO, end-tidal CO2 (FE'CO2) and inspired O2 (FIO2) concentration were recorded every 10 minutes during anaesthesia. Arterial blood gas values were determined 10 minutes after induction of anaesthesia and every 30 minutes thereafter. Changes over time and differences between groups were examined by analysis of variance (anova) for repeated measures followed by Bonferroni-adjusted t-tests for effects over time.

RESULTS

Both MED doses produced mild sedation. The dose of propofol for induction of anaesthesia decreased in a dose-dependent manner: mean (+/-SE) values for group 0 were 4.7 (+/-0.4) mg kg(-1), for group L, 3.2 (+/-0.4) mg kg(-1) and for group H, 2.3 (+/-0.3) mg kg(-1)). The mean (+/-SE) FE'ISO required to maintain anaesthesia was 30% lower in both MED groups [group L: 0.96 (+/-0.07) %; group H: 1.06 (+/-0.09) %] compared with control group values [(1.54 +/- 0.17) %]. Heart rates were constantly higher in the control group with a tendency towards lower arterial blood pressures when compared with the MED groups. Respiratory rates and PaCO2 were similar in all groups while PaO2 increased during anaesthesia with no significant difference between groups. In group H, one animal developed a transient hypoxaemia: PaO2 was 7.4 kPa (55.7 mmHg) 40 minutes after induction of anaesthesia. Arterial pH values and bicarbonate concentrations were higher in the MED groups at all time points.

CONCLUSION AND CLINICAL RELEVANCE

Intramuscular MED doses of 5 and 10 microg kg(-1) reduced the propofol and isoflurane requirements for induction and maintenance of anaesthesia respectively. Cardiovascular variables and blood gas measurements remained stable over the course of anaesthesia but hypoxaemia developed in one of 16 sheep receiving MED.

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.