Clinical review of the pharmacological and anaesthetic effects of alfaxalone in dogs

Effects of hydromorphone alone and combined with medetomidine-vatinoxan or dexmedetomidine on alfaxalone induction dose and mean arterial pressure in dogs anesthetized with sevoflurane

OBJECTIVE

To evaluate the dose of alfaxalone needed for induction of anesthesia following sedation with medetomidine-vatinoxan plus hydromorphone (MVH), dexmedetomidine plus hydromorphone (DH), or hydromorphone (H) alone. A secondary objective included evaluating selected cardiopulmonary variables before, during, and after sedation and general anesthesia with sevoflurane in healthy dogs.

STUDY DESIGN

Prospective, randomized, masked, crossover.

ANIMALS

Eight healthy Beagle dogs, 3-4 years old.

METHODS

All dogs received three intramuscular (IM) treatments: H (0.1 mg kg-1), DH (0.005 mg kg-1 + 0.1 mg kg-1, respectively), or MVH (0.01 mg kg-1 + 0.2 mg kg-1 + 0.1 mg kg-1, respectively) at least 6 days apart. General anesthesia was induced with alfaxalone 20 minutes after treatment administration and maintained for 60 minutes with 2.8% sevoflurane (expired). Sedation scores, selected cardiopulmonary variables, and recovery scores were measured before, during, and after anesthesia at selected timepoints. Mixed-effects ANOVA and ANOVA on ranks were used to evaluate differences between treatments, time, and their interaction, and Tukey-Kramer method was used for post hoc analysis (p < 0.05). Data are presented as mean ± SD or median (range).

RESULTS

Dogs given MVH required a lower dose of alfaxalone for induction of anesthesia (0.77 ± 0.4 mg kg-1) compared to DH and H (1.16 ± 0.34 mg kg-1; p = 0.02, 1.13 ± 0.18 mg kg-1; p = 0.02), and had a higher incidence (50%; p = 0.038) and longer duration [median; 10 (0-35) minutes] of hypotension during sevoflurane anesthesia compared to H [0%; 0 (0-0) minutes; p = 0.040] but not DH (p = 0.272).

CONCLUSIONS AND CLINICAL RELEVANCE

Premedication with MVH provided the greatest alfaxalone-sparing effect. However, this treatment was associated with lower arterial pressures and clinically relevant hypotension. Off-label use of medetomidine-vatinoxan before sevoflurane-based anesthesia should be used with caution due to a high incidence of hypotension.

Comparison of hemodynamic effects of propofol or alfaxalone during induction in dogs

This randomized prospective clinical study aimed to compare the hemodynamic effects of propofol and alfaxalone for the induction of anesthesia in dogs. Thirty-one healthy dogs undergoing various procedures in a private referral center were premedicated with intramuscular acepromazine (0.015 mg/kg) and methadone (0.15 mg/kg). They then received 5 mg/kg of propofol over 30 s for induction, followed by a maintenance dose of 25 mg/kg/h (Group P), or 2 mg/kg of alfaxalone over 30 s for induction, followed by a continuous rate infusion of 10 mg/kg/h (Group A). Heart rate (HR), mean arterial pressure (MAP), and the velocity time integral (VTI) of the aortic blood flow using transthoracic echocardiography were measured before anesthetic induction and every 15 s for 180 s. Dogs not adequately anaesthetized for intubation were excluded from the hemodynamic evaluation. Events of hypotension (any MAP value lower than 60 mmHg) were also recorded. Statistical analyses utilized ANOVA for repeated measures, two-way repeated measures ANOVA, paired t-tests, or Wilcoxon signed rank-test as appropriate. Significance was set at p < 0.05. Two dogs in Group P (2/14) and 3 in Group A (3/17) were excluded from the study because the anesthesia plane was too light to allow intubation. Treatment P resulted in a significant decrease in MAP between 45 and 75 s during the induction period, with no significant variation in HR, VTI, and VTI*HR. In treatment A, HR increases between 60 and 105 s, VTI decreases at 150-180 s. Analysis between groups did not show any difference in MAP (p = 0.12), HR (p = 0.10), VTI (p = 0.22) and VTI*HR (p = 0.74). During induction, hypotension was detected in 3/12 (25%) dogs in Group P and 1/14 (8%) in Group A. In healthy premedicated dogs, propofol and alfaxalone induction produce similar hemodynamic variations. Propofol induction results in a short-term reduction in MAP, whereas alfaxalone induction preserves MAP and cardiac output by significantly increasing heart rate.

Efficacy and safety of alfaxalone compared to propofol in canine refractory status epilepticus: a pilot study

Introduction

Refractory status epilepticus (RSE) is defined as seizure activity that is minimally responsive to first- or second-line antiseizure medications. Constant rate infusion (CRI) intravenous propofol (PPF) is commonly used to treat RSE in dogs and cats. The antiseizure activity of alfaxalone (ALF) in RSE has been demonstrated in various experimental studies. This study compared the clinical efficacy and safety of intramuscular administration followed by CRI infusion of ALF with intravenous administration followed by CRI infusion of PPF to treat canine RSE.

Materials and methods

This was a multicenter, prospective, randomized clinical trial of client-owned dogs referred for status epilepticus that did not respond to first- and second-line drugs. Animals with suspected or confirmed idiopathic or structural epilepsy were included. The dogs were randomly assigned to either the PPF or ALF treatment groups and each group received drug CRI infusions for 6 h. Drug dosages were progressively reduced by 25% every hour from the third hour until suspension after 6 h. Patients were classified as responders or non-responders based on the relapse of epileptic seizures during the 24 h therapy infusion or within 24 h of drug suspension. Univariate statistical analyses were performed.

Results

Twenty dogs were enrolled in the study. Ten (10/20) dogs were randomly allocated to the PPF group and 10 (10/20) to the ALF group. Successful outcomes were obtained in six (6/10) patients in the PPF group and five (5/10) patients in the ALF group. Adverse effects were recorded in six (6/10) and three (3/10) animals in the PPF and ALF groups, respectively. No statistically significant differences in outcomes or the presence of adverse effects were observed between the groups.

Discussion

The results of this preliminary study suggest that ALF can be considered a valid and safe alternative to PPF for the treatment of RSE in dogs, with the additional advantage of intramuscular administration. However, caution should be exercised when using these drugs to provide airway and hemodynamic support.

Comparison of the effects of propofol and alfaxalone on the electrocardiogram of dogs, with particular reference to QT interval

Cardiac electrical activity is often altered by administration of anesthetic drugs. While the effects of propofol in this regard have previously been described in dogs, to date, there are no reports of the effect of alfaxalone. This study investigated the impact of both propofol and alfaxalone on the ECG of 60 dogs, after premedication with acepromazine and methadone. Heart rate increased significantly in both groups. The PR and QRS intervals were significantly increased following propofol while with alfaxalone the QRS duration was significantly increased and ST segment depression was observed. The QT and JT interval were significantly shorter following induction with alfaxalone, but, when corrected (c) for heart rate, QTc and JTc in both groups were significantly greater following induction. When comparing the magnitude of change between groups, the change in RR interval was greater in the alfaxalone group. The change in both QT and JT intervals were significantly greater following alfaxalone, but when QTc and JTc intervals were compared, there were no significant differences between the two drugs. The similarly increased QTc produced by both drugs may suggest comparable proarrhythmic effects.

A dose characterization study evaluating the pharmacodynamics and safety of a concentrated alfaxalone solution (4%) as an intramuscular sedative in dogs

Alfaxalone is a commonly employed veterinary anaesthetic induction and sedation agent. A 4% w/v preserved, aqueous formulation of alfaxalone 'RD0387' (A4%) has recently been developed. To evaluate the sedative effects of A4%, three doses, 5 mg kg-1 (A5); 7.5 mg kg-1 (A7.5) and 10 mg kg-1 (A10) were administered intramuscularly into the epaxial musculature of six healthy adult mixed-breed dogs in an experimental, randomized, blinded, crossover study. Sedation time variables, quality of sedation (including onset of sedation and recovery), physiological variables, response to cephalic vein catheterization and frequency of undesirable events were recorded. Continuous variables were analysed between treatments (one-way ANOVA or restricted maximum likelihood modelling) and within treatments compared with baseline (Tukey's test). Categorical data were analysed between treatments (Kruskal-Wallis' test) and within treatments from baseline (Dunn's test). Significance was set at p < .05. All dogs became sedated (laterally recumbent) and sedation onset was significantly faster in groups A7.5 (9.8 ± 5.3 min) and A10 (9.1 ± 5.6 min) compared to A5 (25.6 ± 16.1 min) (p = .033, p = .027, respectively). Duration of sedation was significantly longer in A10 (168.5 ± 70.6 min) and A7.5 (143.8 ± 58 min) compared to A5 (63.8 ± 28.2 min) (p = .005 and p = .003, respectively). Dogs in A10 had a superior quality of onset of sedation compared to A5 (p = .028). Sedation scores and quality of recovery from sedation were not significantly different between doses. Two dogs (2/6) in A5 were insufficiently sedated for cephalic catheterization. Ataxia was the most frequently observed undesirable event with an overall frequency of 78% (14/18) and 89% (16/18) during sedation onset and recovery, respectively. Overall, A4% administered IM in dogs at 7.5 and 10 mg kg-1 resulted in sufficient sedation for IV catheterization in dogs. To improve the speed and quality of the sedation, it is recommended that future research focuses on combining A4% with other sedative or analgesic drugs.

Effects of Anesthesia on Cerebral Blood Flow and Functional Connectivity of Nonhuman Primates

Nonhuman primates (NHPs) are the closest living relatives of humans and play a critical and unique role in neuroscience research and pharmaceutical development. General anesthesia is usually required in neuroimaging studies of NHPs to keep the animal from stress and motion. However, the adverse effects of anesthesia on cerebral physiology and neural activity are pronounced and can compromise the data collection and interpretation. Functional connectivity is frequently examined using resting-state functional MRI (rsfMRI) to assess the functional abnormality in the animal brain under anesthesia. The fMRI signal can be dramatically suppressed by most anesthetics in a dose-dependent manner. In addition, rsfMRI studies may be further compromised by inter-subject variations when the sample size is small (as seen in most neuroscience studies of NHPs). Therefore, proper use of anesthesia is strongly demanded to ensure steady and consistent physiology maintained during rsfMRI data collection of each subject. The aim of this review is to summarize typical anesthesia used in rsfMRI scans of NHPs and the effects of anesthetics on cerebral physiology and functional connectivity. Moreover, the protocols with optimal rsfMRI data acquisition and anesthesia procedures for functional connectivity study of macaque monkeys are introduced.