The impact of intravenous medetomidine and vatinoxan on echocardiographic evaluation of dogs with stage B1 mitral valve disease

INTRODUCTION/OBJECTIVE

The purpose of this study was to investigate the echocardiographic effects of intravenous medetomidine and vatinoxan in dogs with stage B1 mitral valve disease. We hypothesised medetomidine-vatinoxan would reduce the need for manual restraint during echocardiography without producing detrimental cardiovascular effects or echocardiographic changes.

ANIMALS

Twelve client-owned dogs with stage B1 mitral valve disease.

METHODS

A transthoracic echocardiographic examination was performed before and after sedation with intravenous medetomidine (10 μg/kg) and vatinoxan (200 μg/kg). Vital parameters were also recorded, and the level of sedation was assessed subjectively. The data were analysed with Student's t-tests with an alpha level of <0.05.

RESULTS

End-systolic volume and left ventricular systolic diameter increased (from 0.89 ± 0.19 mL/kg to 1.13 ± 0.29 mL/kg and 0.96 ± 0.12 cm to 1.10 ± 0.10 cm, respectively) and ejection fraction (from 66.33 ± 4.0% to 56.23 ± 9.54%) and fractional shortening (from 36.13 ± 5.42% to 27.24 ± 5.6%) decreased significantly after sedation. End diastolic volume, left ventricular diastolic diameter, and left atrial size remained statistically unchanged, while aortic (from 1.34 ± 0.2 m/s to 0.99 ± 0.14 m/s) and pulmonic (from 0.94 ± 0.16 m/s to 0.66 ± 0.15 m/s) velocities decreased significantly. No dogs had a mean arterial pressure below 65 mmHg. Sedation enabled echocardiographic examination without manual restraint. No adverse effects were observed with the dose studied.

CONCLUSIONS

Echocardiographic parameters were not completely comparable with the baseline values, which should be taken into consideration when evaluating dogs sedated with intravenous medetomidine-vatinoxan.

Comparison between dexmedetomidine and a combination of medetomidine-vatinoxan on muscle tissue saturation in privately-owned adult dogs undergoing intradermal testing

This double-blinded randomized cross-over study compared the muscle tissue oxygen saturation (StO2) measured at the sartorius muscle after intramuscular (IM) injection of dexmedetomidine hydrochloride (HCl) and co-administration of vatinoxan HCl, a peripheral α2-adrenoceptor antagonist, and medetomidine HCl in healthy privately-owned dogs undergoing intradermal testing (IDAT). After written owner consent, dogs received IM injections of either dexmedetomidine (0.5 mg/m2, DEX) or medetomidine (1 mg/m2) and vatinoxan (20 mg/m2) (MVX). Once sedated, intradermal injections were given on the lateral thorax of each dog, and the study was repeated with the alternative sedation on the opposite side one week later. At the end of the study, sedation was reversed with atipamezole (5 mg/m2). Depth of sedation, cardiopulmonary parameters, StO2, and rectal temperature were recorded and compared using mixed effect linear models (α ≤ 0.05). MVX achieved adequate sedation faster [median (interquartile range), 10 (8, 10) minutes] compared to DEX [18 (15, 22) minutes; hazard ratio = 7.44, p = 0.013), with higher scores at 10- and 15-min post-injection. StO2 was significantly reduced for 30 min after injection (p < 0.001), independently of the treatment (p = 0.68). Cardiopulmonary variables favored MVX. However, higher heart rate did not correlate with improved StO2. There was no difference in either subjective or objective assessment of the wheal size between sedations (p > 0.05). Both sedation protocols, MVX and DEX, were deemed suitable for IDAT in dogs, with mild reductions in StO2 measured at the sartorius muscle that were not significantly different between treatments.

Evaluation of cardiovascular effects of intramuscular medetomidine and a medetomidine-vatinoxan combination in Beagle dogs: A randomized blinded crossover laboratory study

OBJECTIVE

To compare the cardiovascular effects of a combination of medetomidine and vatinoxan (MVX) versus medetomidine (MED) alone administered intramuscularly (IM) and to determine whether heart rate (HR) can be used as a surrogate for cardiac output (CO) after the use of medetomidine with or without vatinoxan.

STUDY DESIGN

A randomized, blinded, experimental, crossover study.

ANIMALS

A group of eight healthy Beagle dogs aged 4.6 (2.3-9.4) years and weighing 12.9 (9-14.7) kg, median (range).

METHODS

Each dog was injected with 1 mg m-2 medetomidine with or without 20 mg m-2 vatinoxan IM with a washout period of 7 days. Cardiovascular data and arterial and mixed venous blood gas samples were collected at baseline, 5, 10, 15, 20, 35, 45, 60, 90 and 120 minutes after treatment administration. CO was measured at all time points via thermodilution. Differences between treatments, period and sequence were evaluated with repeated measures analysis of covariance and the relationship between HR and CO was assessed with a repeated measures analysis of variance; p values < 0.05 were deemed significant.

RESULTS

The CO was 47-96% lower after MED than after MVX (p < 0.0001). Increases in systemic, pulmonary arterial and right atrial pressures and oxygen extraction ratio were significantly higher after MED than after MVX (all p < 0.0001). HR was significantly lower after MED and the linear relationship to CO was significant (p < 0.0001).

CONCLUSIONS AND CLINICAL RELEVANCE

Overall, MED affected the cardiovascular system more negatively than MVX, and the difference in cardiovascular function between the treatments can be considered clinically relevant. HR was linearly related to CO, and decreases in HR reflected cardiac performance for dogs sedated with medetomidine with or without vatinoxan.

Effects of vatinoxan on xylazine-induced pulmonary alterations in sheep

It was hypothesized that premedication with vatinoxan, a peripheral α₂ -adrenoceptor antagonist, would mitigate xylazine-induced pulmonary alterations in sheep. Fourteen adult sheep were allotted into two equal groups and premedicated with either vatinoxan (750 µg/kg IV) or saline and sedated 10 min later with xylazine (500 µg/kg IV). Arterial oxygen saturation (SpO₂ ) was measured and respiratory rate (RR) counted at intervals. The sheep were euthanized with IV pentobarbital 10 min after xylazine administration. The severity of pulmonary parenchymal alterations was assessed and graded grossly and histologically and correlations of the morphological changes with SpO₂ evaluated. Following xylazine injection, SpO₂ was significantly higher and RR significantly lower with vatinoxan than with saline and the sheep administered vatinoxan exhibited significantly smaller quantities of tracheal foam than those receiving saline. No significant differences in macroscopic oedema scores were detected between treatments. In contrast, the vatinoxan-treated animals exhibited significantly graver microscopic interstitial alveolar oedema and haemorrhage than saline-treated animals. The histological severity scores did not correlate with changes in SpO₂ . In conclusion, xylazine induced a marked reduction in SpO₂ which was abolished by the prior administration of vatinoxan. The histologically detected alterations after pentobarbital euthanasia with vatinoxan premedication need to be studied further.

Cardiovascular effects of intravenous vatinoxan in wild boars (Sus scrofa) anaesthetised with intramuscular medetomidine-tiletamine-zolazepam

BACKGROUND

The potent sedative medetomidine is a commonly used adjunct for the immobilisation of non-domestic mammals. However, its use is associated with pronounced cardiovascular side effects, such as bradycardia, vasoconstriction and decreased cardiac output. We investigated the effects of the peripherally-acting alpha-2-adrenoceptor antagonist vatinoxan on cardiovascular properties in medetomidine-tiletamine-zolazepam anaesthetised wild boar (Sus scrofa).

METHODS

Twelve wild boars, anaesthetised twice with medetomidine (0.1 mg/kg) and tiletamine/zolazepam (2.5 mg/kg) IM in a randomised, crossover study, were administered (0.1 mg/kg) vatinoxan or an equivalent volume of saline IV (control). Cardiovascular variables, including heart rate (HR), mean arterial blood pressure (MAP), pulmonary artery pressure (PAP), pulmonary artery occlusion pressure (PAOP) and cardiac output (CO), were assessed 5 min prior to vatinoxan/saline administration until the end of anaesthesia 30 min later.

RESULTS

MAP (p < 0.0001), MPAP (p < 0.001) and MPAOP (p < 0.0001) significantly decreased from baseline after vatinoxan until the end of anaesthesia. HR increased significantly (p < 0.0001) from baseline after vatinoxan administration. However, the effect on HR subsided 3 min after vatinoxan. All variables remained constant after saline injection. There was no significant effect of vatinoxan or saline on CO.

CONCLUSION

Vatinoxan significantly reduced systemic and pulmonary artery hypertension, induced by medetomidine in wild boar.

Combined effects of dexmedetomidine and vatinoxan infusions on minimum alveolar concentration and cardiopulmonary function in sevoflurane-anesthetized dogs

OBJECTIVE

To evaluate the effects of combined infusions of vatinoxan and dexmedetomidine on inhalant anesthetic requirement and cardiopulmonary function in dogs.

STUDY DESIGN

Prospective experimental study.

METHODS

A total of six Beagle dogs were anesthetized to determine sevoflurane minimum alveolar concentration (MAC) prior to and after an intravenous (IV) dose (loading, then continuous infusion) of dexmedetomidine (4.5 μg kg^-1 hour^-1) and after two IV doses of vatinoxan in sequence (90 and 180 μg kg^-1 hour^-1). Blood was collected for plasma dexmedetomidine and vatinoxan concentrations. During a separate anesthesia, cardiac output (CO) was measured under equivalent MAC conditions of sevoflurane and dexmedetomidine, and then with each added dose of vatinoxan. For each treatment, cardiovascular variables were measured with spontaneous and controlled ventilation. Repeated measures analyses were performed for each response variable; for all analyses, p < 0.05 was considered significant.

RESULTS

Dexmedetomidine reduced sevoflurane MAC by 67% (0.64 ± 0.1%), mean ± standard deviation in dogs. The addition of vatinoxan attenuated this to 57% (0.81 ± 0.1%) and 43% (1.1 ± 0.1%) with low and high doses, respectively, and caused a reduction in plasma dexmedetomidine concentrations. Heart rate and CO decreased while systemic vascular resistance increased with dexmedetomidine regardless of ventilation mode. The co-administration of vatinoxan dose-dependently modified these effects such that cardiovascular variables approached baseline.

CONCLUSIONS AND CLINICAL RELEVANCE

IV infusions of 90 and 180 μg kg^-1 hour^-1 of vatinoxan combined with 4.5 μg kg^-1 hour^-1 dexmedetomidine provide a meaningful reduction in sevoflurane requirement in dogs. Although sevoflurane MAC-sparing properties of dexmedetomidine in dogs are attenuated by vatinoxan, the cardiovascular function is improved. Doses of vatinoxan >180 μg kg^-1 hour^-1 might improve cardiovascular function further in combination with this dose of dexmedetomidine, but beneficial effects on anesthesia plane and recovery quality may be lost.

Investigation of the effects of vatinoxan on somatic and visceral antinociceptive efficacy of medetomidine in dogs

OBJECTIVE

To determine whether concurrent vatinoxan administration affects the antinociceptive efficacy of medetomidine in dogs at doses that provide circulating dexmedetomidine concentrations similar to those produced by medetomidine alone.

ANIMALS

8 healthy Beagles.

PROCEDURES

Dogs received 3 IV treatments in a randomized crossover-design trial with a 2-week washout period between experiments (medetomidine [20 μg/kg], medetomidine [20 μg/kg] and vatinoxan [400 μg/kg], and medetomidine [40 μg/kg] and vatinoxan [800 μg/kg]; M20, M20V400, and M40V800, respectively). Sedation, visceral and somatic nociception, and plasma drug concentrations were assessed. Somatic and visceral nociception measurements and sedation scores were compared among treatments and over time. Sedation, visceral antinociception, and somatic antinociception effects of M20V400 and M40V800 were analyzed for noninferiority to effects of M20, and plasma drug concentration data were assessed for equivalence between treatments.

RESULTS

Plasma dexmedetomidine concentrations after administration of M20 and M40V800 were equivalent. Sedation scores, visceral nociception measurements, and somatic nociception measurements did not differ significantly among treatments within time points. Overall sedative effects of M20V400 and M40V800 and visceral antinociceptive effects of M40V800 were noninferior to those produced by M20. Somatic antinociception effects of M20V400 at 10 minutes and M40V800 at 10 and 55 minutes after injection were noninferior to those produced by M20.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested coadministration with vatinoxan did not substantially diminish visceral antinociceptive effects of medetomidine when plasma dexmedetomidine concentrations were equivalent to those produced by medetomidine alone. For somatic antinociception, noninferiority of treatments was detected at some time points.

Effects of intramuscular vatinoxan (MK-467), co-administered with medetomidine and butorphanol, on cardiopulmonary and anaesthetic effects of intravenous ketamine in dogs

OBJECTIVE

To investigate the impact of intramuscular (IM) co-administration of the peripheral α₂-adrenoceptor agonist vatinoxan (MK-467) with medetomidine and butorphanol prior to intravenous (IV) ketamine on the cardiopulmonary and anaesthetic effects in dogs, followed by atipamezole reversal.

STUDY DESIGN

Randomized, masked crossover study.

ANIMALS

A total of eight purpose-bred Beagle dogs aged 3 years.

METHODS

Each dog was instrumented and administered two treatments 2 weeks apart: medetomidine (20 μg kg^-1) and butorphanol (100 μg kg^-1) premedication with vatinoxan (500 μg kg^-1; treatment MVB) or without vatinoxan (treatment MB) IM 20 minutes before IV ketamine (4 mg kg^-1). Atipamezole (100 μg kg^-1) was administered IM 60 minutes after ketamine. Heart rate (HR), mean arterial (MAP) and central venous (CVP) pressures and cardiac output (CO) were measured; cardiac (CI) and systemic vascular resistance (SVRI) indices were calculated before and 10 minutes after MVB or MB, and 10, 25, 40, 55, 70 and 100 minutes after ketamine. Data were analysed with repeated measures analysis of covariance models. A p-value <0.05 was considered statistically significant. Sedation, induction, intubation and recovery scores were assessed.

RESULTS

At most time points, HR and CI were significantly higher, and SVRI and CVP significantly lower with MVB than with MB. With both treatments, SVRI and MAP decreased after ketamine, whereas HR and CI increased. MAP was significantly lower with MVB than with MB; mild hypotension (57-59 mmHg) was recorded in two dogs with MVB prior to atipamezole administration. Sedation, induction, intubation and recovery scores were not different between treatments, but intolerance to the endotracheal tube was observed earlier with MVB.

CONCLUSIONS AND CLINICAL RELEVANCE

Haemodynamic performance was improved by vatinoxan co-administration with medetomidine-butorphanol, before and after ketamine administration. However, vatinoxan was associated with mild hypotension after ketamine with the dose used in this study. Vatinoxan shortened the duration of anaesthesia.

Cardiovascular and sedation reversal effects of intramuscular administration of atipamezole in dogs treated with medetomidine hydrochloride with or without the peripheral α2-adrenoceptor antagonist vatinoxan hydrochloride

OBJECTIVE

To investigate the cardiovascular and sedation reversal effects of IM administration of atipamezole (AA) in dogs treated with medetomidine hydrochloride (MED) or MED and vatinoxan (MK-467).

ANIMALS

8 purpose-bred, 2-year-old Beagles.

PROCEDURES

A randomized, blinded, crossover study was performed in which each dog received 2 IM treatments at a ≥ 2-week interval as follows: injection of MED (20 μg/kg) or MED mixed with 400 μg of vatinoxan/kg (MEDVAT) 30 minutes before AA (100 μg/kg). Sedation score, heart rate, mean arterial and central venous blood pressures, and cardiac output were recorded before and at various time points (up to 90 minutes) after AA. Cardiac and systemic vascular resistance indices were calculated. Venous blood samples were collected at intervals until 210 minutes after AA for drug concentration analysis.

RESULTS

Heart rate following MED administration was lower, compared with findings after MEDVAT administration, prior to and at ≥ 10 minutes after AA. Mean arterial blood pressure was lower with MEDVAT than with MED at 5 minutes after AA, when its nadir was detected. Overall, cardiac index was higher and systemic vascular resistance index lower, indicating better cardiovascular function, in MEDVAT-atipamezole-treated dogs. Plasma dexmedetomidine concentrations were lower and recoveries from sedation were faster and more complete after MEDVAT treatment with AA than after MED treatment with AA.

CONCLUSIONS AND CLINICAL RELEVANCE

Atipamezole failed to restore heart rate and cardiac index in medetomidine-sedated dogs, and relapses into sedation were observed. Coadministration of vatinoxan with MED helped to maintain hemodynamic function and hastened the recovery from sedation after AA in dogs.

Alternatives to Opioid Analgesia in Small Animal Anesthesia: Alpha-2 Agonists

Alpha-2 agonists have potent analgesic effects, in addition to their sedative actions. Alpha-2 agonists provide analgesia through any of several routes of administration, including parenteral, oral, epidural or intrathecal and intraarticular, because of spinal and supraspinal actions. Systemic doses are short acting, whereas local administration at the site of action result in longer analgesic effects. The potent cardiovascular and respiratory effects of alpha-2 agonists should be considered when used as analgesics.

Concentrations of medetomidine enantiomers and vatinoxan, an α2-adrenoceptor antagonist, in plasma and central nervous tissue after intravenous coadministration in dogs

OBJECTIVE

To quantify the peripheral selectivity of vatinoxan (L-659,066, MK-467) in dogs by comparing the concentrations of vatinoxan, dexmedetomidine and levomedetomidine in plasma and central nervous system (CNS) tissue after intravenous (IV) coadministration of vatinoxan and medetomidine.

STUDY DESIGN

Experimental, observational study.

ANIMALS

A group of six healthy, purpose-bred Beagle dogs (four females and two males) aged 6.5 ± 0.1 years (mean ± standard deviation).

METHODS

All dogs were administered a combination of medetomidine (40 μg kg^-1) and vatinoxan (800 μg kg^-1) as IV bolus. After 20 minutes, the dogs were euthanized with an IV overdose of pentobarbital (140 mg kg^-1) and both venous plasma and CNS tissues (brain, cervical and lumbar spinal cord) were harvested. Concentrations of dexmedetomidine, levomedetomidine and vatinoxan in all samples were quantified by liquid chromatography-tandem mass spectrometry and data were analyzed with nonparametric tests with post hoc corrections where appropriate.

RESULTS

All dogs became deeply sedated after the treatment. The CNS-to-plasma ratio of vatinoxan concentration was approximately 1:50, whereas the concentrations of dexmedetomidine and levomedetomidine in the CNS were three- to seven-fold of those in plasma.

CONCLUSIONS AND CLINICAL RELEVANCE

With the doses studied, these results confirm the peripheral selectivity of vatinoxan in dogs, when coadministered IV with medetomidine. Thus, it is likely that vatinoxan preferentially antagonizes α₂-adrenoceptors outside the CNS.

Changes in energy metabolism, and levels of stress-related hormones and electrolytes in horses after intravenous administration of romifidine and the peripheral α-2 adrenoceptor antagonist vatinoxan

Background

Romifidine, an α-2 adrenoceptor agonist, is a widely-used sedative in equine medicine. Besides the desired sedative and analgesic actions, α-2 adrenoceptor agonists have side effects like alterations of plasma concentrations of glucose and certain stress-related hormones and metabolites in various species. Vatinoxan (previously known as MK-467), in turn, is an antagonist of α-2 adrenoceptors. Because vatinoxan does not cross the blood brain barrier in significant amounts, it has only minor effect on sedation induced by α-2 adrenoceptor agonists. Previously, vatinoxan is shown to prevent the hyperglycaemia, increase of plasma lactate concentration and the decrease of insulin and non-esterified free fatty acids (FFAs) caused by α-2 adrenoceptor agonists in different species. The aim of our study was to investigate the effects of intravenous romifidine and vatinoxan, alone and combined, on plasma concentrations of glucose and some stress-related hormones and metabolites in horses.

Results

Plasma glucose concentration differed between all intravenous treatments: romifidine (80 μg/kg; ROM), vatinoxan (200 μg/kg; V) and the combination of these (ROM + V). Glucose concentration was the highest after ROM and the lowest after V. Serum FFA concentration was higher after V than after ROM or ROM + V. The baseline serum concentration of insulin varied widely between the individual horses. No differences were detected in serum insulin, cortisol or plasma adrenocorticotropic hormone (ACTH) concentrations between the treatments. Plasma lactate, serum triglyceride or blood sodium and chloride concentrations did not differ from baseline or between the treatments. Compared with baseline, plasma glucose concentration increased after ROM and ROM + V, serum cortisol, FFA and base excess increased after all treatments and plasma ACTH concentration increased after V. Serum insulin concentration decreased after V and blood potassium decreased after all treatments.

Conclusions

Romifidine induced hyperglycaemia, which vatinoxan partially prevented despite of the variations in baseline levels of serum insulin. The effects of romifidine and vatinoxan on the insulin concentration in horses need further investigation.

Cardiovascular effects of premedication with medetomidine alone and in combination with MK-467 or glycopyrrolate in dogs subsequently anesthetized with isoflurane

OBJECTIVE To compare cardiovascular effects of premedication with medetomidine alone and with each of 3 doses of MK-467 or after glycopyrrolate in dogs subsequently anesthetized with isoflurane. ANIMALS 8 healthy purpose-bred 5-year-old Beagles. PROCEDURES In a randomized crossover study, each dog received 5 premedication protocols (medetomidine [10 μg/kg, IV] alone [MED] and in combination with MK-467 at doses of 50 [MMK50], 100 [MMK100], and 150 [MMK150] μg/kg and 15 minutes after glycopyrrolate [10 μg/kg, SC; MGP]), with at least 14 days between treatments. Twenty minutes after medetomidine administration, anesthesia was induced with ketamine (0.5 mg/kg, IV) and midazolam (0.1 mg/kg, IV) increments given to effect and maintained with isoflurane (1.2%) for 50 minutes. Cardiovascular variables were recorded, and blood samples for determination of plasma dexmedetomidine, levomedetomidine, and MK-467 concentrations were collected at predetermined times. Variables were compared among the 5 treatments. RESULTS The mean arterial pressure and systemic vascular resistance index increased following the MED treatment, and those increases were augmented and obtunded following the MGP and MMK150 treatments, respectively. Mean cardiac index for the MMK100 and MMK150 treatments was significantly greater than that for the MGP treatment. The area under the time-concentration curve to the last sampling point for dexmedetomidine for the MMK150 treatment was significantly lower than that for the MED treatment. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated concurrent administration of MK-467 with medetomidine alleviated medetomidine-induced hemodynamic changes in a dose-dependent manner prior to isoflurane anesthesia. Following MK-467 administration to healthy dogs, mean arterial pressure was sustained at acceptable levels during isoflurane anesthesia.

The impact of medetomidine on the protein-binding characteristics of MK-467 in canine plasma

This study determined the unbound fraction of the peripheral α2 -adrenoceptor antagonist MK-467 alone and combined with medetomidine. MK-467 (0.1, 1 and 10 μm) was incubated in canine plasma with and without medetomidine (molar ratio 20:1), with human serum albumin (HSA) and with α1-acid glycoprotein (AGP). Rapid equilibrium dialysis was used for the measurement of protein binding. All samples were analysed by liquid chromatography and tandem mass spectrometry to obtain the unbound fraction (fu ) of MK-467. Unbound fractions (fu ) of MK-467 in canine plasma (mean ± standard deviation) were 27.6 ± 3.5%, 26.6 ± 0.9% and 42.4 ± 1.2% at 0.1, 1.0 and 10 μm concentrations, respectively. In the presence of medetomidine, fu were 27.5 ± 0.4%, 26.6 ± 0.9% and 41.0 ± 2.4%. The fu of MK-467 in HSA were 50.1 ± 2.5% at 0.1 μm, 49.4 ± 1.2% at 1.0 μm and 56.7 ± 0.5% at 10 μm. fu of MK-467 in AGP was 56.3 ± 3.7% at 0.1 μm, 54.6 ± 5.6% at 1.0 μm and 65.3 ± 0.4% at 10 μm. Protein binding of MK-467 was approximately 70% between 0.1 and 1.0 μm. Medetomidine had no apparent effect on the protein binding of MK-467.

Potentiation of Glibenclamide Hypoglycaemia in Mice by MK-467, a Peripherally Acting Alpha2-Adrenoceptor Antagonist

Pharmacological antagonism and genetic depletion of pancreatic α2A-adrenoceptors increase insulin secretion in mice and enhance the insulinotropic action of glibenclamide, a representative of the sulphonylurea class of insulin secretagogues used in the therapy of type 2 diabetes. Antagonism of α2-adrenoceptors in the central nervous system (CNS) causes tachycardia and hypertension, making generalized α2-adrenoceptor blockade unfavourable for clinical use despite its potential to decrease blood glucose levels. The purpose of this study was to test the acute effects of the peripherally acting α2-adrenoceptor antagonist MK-467 alone and in combination with glibenclamide in non-diabetic C57BL/6N mice. Cardiovascular safety was assessed in freely moving mice with radiotelemetry. Dose-dependent decreases in blood glucose and increases in plasma insulin concentrations were seen with the combination of MK-467 and glibenclamide; the combinations were much more potent than glibenclamide or MK-467 alone. Furthermore, MK-467 had no effect on mean arterial pressure or heart rate in freely moving mice and did not prevent the centrally mediated hypotensive effect of the α2-adrenoceptor agonist medetomidine. Thus, peripheral blockade of α2-adrenoceptors does not evoke the same cardiovascular adverse effects as antagonism of CNS α2-adrenoceptors. The current results indicate that the combined use of small doses of a peripherally acting α2-adrenoceptor antagonist with a sulphonylurea drug could provide a novel option for the treatment of type 2 diabetes, especially in patients with increased tonic α2-adrenoceptor-mediated inhibition of insulin secretion.

Haemodynamic interactions of medetomidine and the peripheral alpha-2 antagonist MK-467 during step infusions in isoflurane-anaesthetised dogs

The haemodynamic interactions of a step infusion with medetomidine (MED) and the peripherally acting alpha-2 antagonist MK-467 (MK) were compared with MED infused alone in isoflurane-anaesthetised dogs. Eight purposely-bred Beagles were used in a randomised crossover study. Anaesthesia was induced with propofol intravenously (IV) and maintained with isoflurane in oxygen. Dogs received 1.25 µg/kg MED as a 1 min loading dose IV, along with a step-down MED infusion at rates of 8.0 µg/kg/h (step 1: 0-20 min), 5.5 µg/kg/h (step 2: 20-40 min) and 4.0 µg/kg/h (step 3: 40-95 min). Five minutes after starting the MED infusion, the dogs received MK-467 in a step-up infusion at rates of 100 µg/kg/h (step 1: 5-35 min), 200 µg/kg/h (step 2: 35-65 min) and 500 µg/kg/h (step 3: 65-95 min). Heart rate (HR), systolic (SAP) and mean arterial (MAP) blood pressures and arteriovenous oxygen content differences (a-vO2 diff) were calculated. Plasma drug concentrations were analysed. Repeated-measures general linear mixed models with Bonferroni correction were used for statistical analyses. MED infusion alone increased SAP maximally by 24.9%, MAP by 34.7% and a-vO2 diff by 222.5%, and reduced HR by 32.3%, but these changes were significantly attenuated by MK-467. Most MED effects returned to baseline during step 2 of MK-467 infusion and step 3 of MED infusion (MED/MK-467 ratio 1:18 to 1:50). Plasma concentrations of MED tended to be lower with the addition of MK-467. The use of step infusions helped to narrow down the therapeutic range for the MED/MK-467 infusion dose ratio during isoflurane anaesthesia in dogs.

The cardiopulmonary effects of a peripheral alpha-2-adrenoceptor antagonist, MK-467, in dogs sedated with a combination of medetomidine and butorphanol

OBJECTIVE

To compare the cardiopulmonary effects of intravenous (IV) and intramuscular (IM) medetomidine and butorphanol with or without MK-467.

STUDY DESIGN

Prospective, randomized experimental cross-over.

ANIMALS

Eight purpose-bred beagles (two females, six males), 3-4 years old and weighing 14.5 ±1.6 kg (mean ± SD).

METHODS

All dogs received four different treatments as follows: medetomidine 20 μg kg(-1) and butorphanol tartrate 0.1 mg kg(-1) IV and IM (MB), and MB combined with MK-467,500 μg kg(-1) (MBMK) IV and IM. Heart rate (HR), arterial blood pressures (SAP, MAP, DAP), central venous pressure (CVP), cardiac output, respiratory rate (fR ), rectal temperature (RT) were measured and arterial blood samples were obtained for gas analysis at baseline and at 3, 10, 20, 30, 45 and 60 minutes after drug administration. The cardiac index (CI), systemic vascular resistance index (SVRI) and oxygen delivery index (DO2 I) were calculated. After the follow-up period atipamezole 50 μg kg(-1) IM was given to reverse sedation.

RESULTS

HR, CI and DO2 I were significantly higher with MBMK after both IV and IM administration. Similarly, SAP, MAP, DAP, CVP, SVRI and RT were significantly lower after MBMK than with MB. There were no differences in fR between treatments, but arterial partial pressure of oxygen decreased transiently after all treatments. Recoveries were uneventful following atipamezole administration after all treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

MK-467 attenuated the cardiovascular effects of a medetomidine-butorphanol combination after IV and IM administration.