Medetomidine/midazolam/ketamine anaesthesia in ferrets: effects on cardiorespiratory parameters and evaluation of plasma drug concentrations

Pharmacokinetics of hydrorphone hydrochloride after intravenous and subcutaneous administration in ferrets (Mustela putorius furo)

OBJECTIVE

To determine the pharmacokinetic profile of hydromorphone 0.2 mg kg-1 administered by the intravenous (IV) and subcutaneous (SC) route in ferrets.

STUDY DESIGN

Randomized, crossover study.

ANIMALS

A group of eight adult ferrets weighting (mean ± standard deviation) 1.02 ± 0.22 kg.

METHODS

Hydromorphone hydrochloride 0.2 mg kg-1 was administered IV or SC with a washout period of 7 days. Blood samples were collected from a jugular catheter before administration of hydromorphone and at 5, 10, 15, 20, 30, 45, 60, 90, 120, 240, 360, 480 and 720 minutes after hydromorphone administration. Plasma hydromorphone concentrations were determined by liquid chromatography/tandem mass spectrometry. Data were analyzed using a non-linear mixed effects model.

RESULTS

The hydromorphone effective half-life was (t1/2) 45 min-1. Systemic clearance (Cls) and the volume of distribution (Vdss) following IV administration were 84.8 mL kg-1 min-1 and 5.59 L kg-1, respectively. The maximum observed plasma concentration was 59.53 ± 14.02 ng mL-1 within 10 minutes following SC administration. The SC bioavailability was 102.0%.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of IV and SC hydromorphone (0.2 mg kg-1) was characterized by a high clearance, short terminal half-life and large volume of distribution. Hydromorphone plasma concentrations remained greater than 2 ng mL-1 for 2 hours in most ferrets, a threshold reported to provide antinociceptive effects in other species. Hydromorphone was well absorbed following SC injection, providing an alternative administration route for clinical use in ferrets.

SEDATIVE AND CARDIORESPIRATORY EFFECTS OF INTRAMUSCULAR ALFAXALONE AND BUTORPHANOL AT TWO DOSAGES IN FERRETS (MUSTELA PUTORIUS FURO)

Veterinary care of ferrets often requires chemical restraint. This study hypothesized that IM alfaxalone and butorphanol would result in clinically useful sedation without clinically relevant cardiorespiratory effects. Twelve healthy 15-mo-old ferrets of equal sexes weighing 0.75 to 1.66 kg were enrolled. Using a prospective, blinded design, ferrets randomly received either IM alfaxalone 2.5 mg/kg and butorphanol 0.2 mg/kg (low dose [LD]) or IM alfaxalone 5 mg/kg and butorphanol 0.2 mg/kg (high dose [HD]) (n = 6/group). Sedation times and induction and recovery scores were recorded by a blinded observer. Anesthetic monitor placement was attempted in all recumbent ferrets, and physiologic parameters and reflexes were recorded every 5 min until return of spontaneous movement. Data were assessed for normality using a Shapiro-Wilk normality test and analyzed by two-sample t test or Mann-Whitney U test; one ferret in HD was excluded. Ferrets in LD and HD exhibited moderate and marked sedation, with one of six and four of five ferrets tolerating monitor placement, respectively. Mean ± SD time to first effects, recumbency, and recovery in LD and HD was 2.30 ± 1.13 and 2.054 ± 1.12 (P = 0.7240), 2.87 ± 1.25 and 2.72 ± 1.41 (P = 0.8529), and 65.43 ± 32.43 and 52.30 ± 13.19 (P = 0.4212), respectively. Median (range) duration of recumbency in LD and HD was 31.12 (25.58-115.72) and 35.47 (28.27-44.42) min (P = 0.3290), respectively. Among monitored ferrets, transient mild hypotension and hypoxemia were observed. Intramuscular alfaxalone 5 mg/kg with butorphanol 0.2 mg/kg provided clinically useful sedation in ferrets with mild transient cardiorespiratory derangements.

Injection anaesthesia with fentanyl-midazolam-medetomidine in adult female mice: importance of antagonization and perioperative care

Injection anaesthesia is commonly used in laboratory mice; however, a disadvantage is that post-anaesthesia recovery phases are long. Here, we investigated the potential for shortening the recovery phase after injection anaesthesia with fentanyl-midazolam-medetomidine by antagonization with naloxone-flumazenil-atipamezole. In order to monitor side-effects, the depth of anaesthesia, heart rate (HR), core body temperature (BT) and concentration of blood gases, as well as reflex responses, were assessed during a 50 min anaesthesia. Mice were allowed to recover from the anaesthesia in their home cages either with or without antagonization, while HR, core BT and spontaneous home cage behaviours were recorded for 24 h. Mice lost righting reflex at 330 ± 47 s after intraperitoneal injection of fentanyl-midazolam-medetomidine. During anaesthesia, HR averaged 225 ± 23 beats/min, respiratory rate and core BT reached steady state at 131 ± 15 breaths/min and 34.3 ± 0.25℃, respectively. Positive pedal withdrawal reflex, movement triggered by tail pinch and by toe pinch, still occurred in 25%, 31.2% and 100% of animals, respectively. Arterial blood gas analysis revealed acidosis, hypoxia, hypercapnia and a marked increase in glucose concentration. After anaesthesia reversal by injection with naloxone-flumazenil-atipamezole, animals regained consciousness after 110 ± 18 s and swiftly returned to physiological baseline values, yet they displayed diminished levels of locomotion and disrupted circadian rhythm. Without antagonization, mice showed marked hypothermia (22 ± 1.9℃) and bradycardia (119 ± 69 beats/min) for several hours. Fentanyl-midazolam-medetomidine provided reliable anaesthesia in mice with reasonable intra-anaesthetic side-effects. Post-anaesthetic period and related adverse effects were both reduced substantially by antagonization with naloxone-flumazenil-atipamezole.

Chemical immobilization and anesthesia of free-living aardvarks (Orycteropus afer) with ketamine-medetomidine-midazolam and isoflurane

Abstract We evaluated the effectiveness of a ketamine-medetomidine-midazolam drug combination administered intramuscularly by remote injection followed by isoflurane anesthesia in free-living aardvarks (Orycteropus afer). Seven aardvarks weighing 33-45 kg were immobilized to perform surgical implantation of temperature loggers using 3.8 mg/kg ketamine, 0.1 mg/kg medetomidine, and 0.25 mg/kg midazolam. Immobilized aardvarks were transported to a surgical theater and received 0.5-1% isoflurane in oxygen after tracheal intubation. After surgery, medetomidine was antagonized with 0.5 mg/kg atipamezole, and aardvarks were released at the site of capture. We recorded induction and recovery times, clinical and physiologic parameters, and conducted blood gas analyses before and during isoflurane administration. Aardvarks showed initial effects within 3 min and reached lateral recumbency within 7 min after drug administration. Heart rate (50-67 beats/min), respiratory rate (10-15 breaths/min), oxygen hemoglobin saturation (SaO2; 90-97%), and rectal temperature (34.0-37.5 C) were within acceptable physiologic ranges. Mean arterial blood pressure was initially high (146 ± 12 mmHg), but the hypertension resolved over time. Rectal temperature dropped significantly during anesthesia. Four animals had to be treated to relieve apnea. Blood gas analyses revealed mild to moderate hypercapnia but no hypoxaemia. The ketamine-medetomidine-midazolam combination provided effective immobilization. Combined with a low concentration of isoflurane, it can be used for prolonged surgical procedures in wild aardvarks. However, caution is needed, and monitoring of clinical parameters is required.