Pharmacokinetics of morphine and plasma concentrations of morphine-6-glucuronide following morphine administration to dogs

Morphine in donkeys: Antinociceptive effect and preliminary pharmacokinetics

BACKGROUND

Morphine is the prototypical μ-opioid receptor agonist used to provide analgesia in veterinary species. Its effects are well-described in horses but not donkeys.

OBJECTIVES

To determine the antinociceptive effects of two doses of morphine in donkeys. To describe preliminary pharmacokinetic parameters of morphine in donkeys.

STUDY DESIGN

In vivo experiment.

METHODS

Eight adult castrated male donkeys were given intravenous (IV) 0.9% saline, morphine 0.1 mg/kg bwt (LDM), or morphine 0.5 mg/kg bwt (HDM) in a randomised order with a minimum 1-week washout period. Mechanical nociceptive thresholds (MNTs) were determined by a blinded investigator pre-injection and 15, 30, 45, 60, 90, 120, 150, 180, 210, 240, 300, and 360 min post-injection. Venous blood samples were collected pre-injection and 2, 5, 10, 15, 30, 45, 60, 90, and 120 min post-injection. Data were analysed using Friedman's test with Dunn's post hoc test for multiple comparisons. Pharmacokinetic parameters were calculated for the HDM treatment.

RESULTS

Baseline MNT was [median (interquartile range)] 8.9 (7.1-10.3) N and did not differ between treatments. Peak MNTs occurred at 60 min for both LDM (16.2 N) and HDM (25.0 N) treatments. MNTs after HDM treatment were higher than saline (p < 0.04) at 15, 60, 90, 120, 150, 180, 240, and 300 min post-injection. MNTs after LDM treatment were higher than baseline (p < 0.05) at 45 and 60 min post-injection. Terminal half-life for HDM was (mean ± SD) 51.0 ± 10.7 min, the volume of distribution at steady-state 2.07 ± 0.33 L/min and clearance 49.2 ± 4.16 ml * min/kg using noncompartmental analysis. The concentration of morphine-3-glucuronide (M3G) was higher than morphine-6-glucuronide (M6G) at all sampled time points.

MAIN LIMITATIONS

Short duration of plasma sampling for pharmacokinetic analysis; lack of objective measure of gastrointestinal function.

CONCLUSIONS

The HDM treatment provided mechanical antinociception in donkeys with no significant adverse effects.

Immediate Postoperative Analgesia of Nalbuphine-Ketamine Combination Compared with Ketamine Alone in Xylazine-Sedated Goats Undergoing Left Flank Laparotomy

Goats have been used as animal models in research, and the need for achieving safer anesthesia for research or surgical intervention is gaining much attention. The objective of this study was to evaluate intraoperative effects and the immediate postoperative analgesia of nalbuphine–ketamine regimen in goats. Twenty clinically healthy adult female crossbred goats weighing 14 ± 2 kg were allocated randomly into each of two equally sized groups. All animals were sedated with intramuscular (IM) xylazine (0.07 mg/kg), then anesthesia was intravenously (IV) induced with ketamine alone (10 mg/kg) (XK group), or a combination of nalbuphine (0.5 mg/kg) and ketamine (5 mg/kg) (XNK group). Following induction, left flank laparotomy was performed and then sutured. The quality of anesthesia and immediate postoperative analgesia was evaluated. Immediate postoperative analgesia was assessed up to 5 h after standing, using a modified Unesp–Botucatu acute composite pain scale (USAPS). Serum cortisol, glucose, insulin, and C-reactive protein (CRP) were measured at ½, 1, 2, 4, 6, 12, and 24 h, postoperatively (PO). The USAPS pain scores were significantly lower in the XNK compared to the XK group (p < 0.05). The XNK group exhibited a statistically significant difference in the level of serum cortisol at ½ and 1 h PO (p = 0.018 and 0.045, respectively) compared to the XK group. At 2, 4, 6 h PO, CRP significantly decreased (p = 0.023, 0.040 and 0.005, respectively) in the XNK compared to the XK group. Nalbuphine–ketamine produced an acceptable induction of anesthesia and recovery compared to ketamine. Recovery with nalbuphine–ketamine was faster and better quality. The USAPS pain scores were lower in nalbuphine–ketamine, indicating that this novel combination produces better postoperative pain control than ketamine alone.

Intravenous dexmedetomidine, morphine, or a combination can result in gallbladder wall thickening; with no significant association with plasma histamine concentrations

The gallbladder is routinely evaluated during ultrasonographic examinations in dogs. However, published studies describing the effects of sedative agents on gallbladder wall thickness are currently lacking. The aims of this prospective, blinded, randomized crossover pilot study were to test hypotheses that IV morphine would result in gallbladder wall thickening, that morphine administration would increase plasma histamine concentrations, and that combining IV morphine with dexmedetomidine would potentiate gallbladder wall thickening. Six healthy Beagle dogs were sedated with intravenous (IV) morphine 0.4 mg/kg (group M), dexmedetomidine 7 μg/kg (group D), or a combination of the two (group MD). Physiologic parameters were measured at baseline and at regular intervals until the last ultrasonographic scan. Ultrasonographic scans were performed at baseline, 90 s, and at 5, 15, 30, 45, 60, 90, and 120 min. Plasma histamine samples were taken at baseline, 90 s, and 5 and 60 min. Cochran's Q-test was used to compare gallbladder wall thickening between groups, while the association between histamine plasma concentration and gallbladder wall thickness was compared with a mixed-effects model. Baseline gallbladder wall thickness was not significantly different between groups. Six of 18 treatments/dogs (33%) developed gallbladder thickening, with no difference between groups. There was no significant difference in baseline plasma histamine concentrations between groups, and no association between plasma histamine concentration and gallbladder wall thickness. Gallbladder wall thickening was observed in at least one dog in each group, therefore caution is recommended for gallbladder wall thickness ultrasonographic interpretation in dogs when these drugs have been administered.

Pharmacokinetic profiles of three dose rates of morphine sulfate following single intravenous, intramuscular, and subcutaneous administration in the goat

This study aimed to evaluate pharmacokinetic profiles of morphine in goats following a single dose administered intravenously, intramuscularly, or subcutaneously at 0.1 mg/kg, 0.25 mg/kg, and 0.4 mg/kg. Study population included eight healthy adult goats in a randomized cross-over study. Serial plasma samples were collected and morphine was quantified using high-performance liquid chromatography/mass spectrometry. Data fit a two-compartment model following intravenous administration and a non-compartmental model following both intramuscular and subcutaneous administration. Plasma elimination half-life was 2.88 ± 1.13 h (0.1 mg/kg), 2.30 ± 0.49 h (0.25 mg/kg), and 2.67 ± 0.82 h (0.4 mg/kg) following IV morphine. Intramuscular Cmax values were 13.4 ± 2.77 ng/ml (0.1 mg/kg), 34 ± 11.50 ng/ml (0.25 mg/kg), and 68.9 ± 24.5 ng/ml (0.4 mg/kg). Intramuscular Tmax f(h) or IM dosing (in hrs) was 0.19 ± 0.14 (0.1 mg/kg), 0.24 ± 0.24 (0.25 mg/kg), and 0.21 ± 0.24 (0.4 mg/kg). Subcutaneous Cmax values were 9.88 ± 3.31 ng/ml (0.1 mg/kg), 28.5 ± 11.6 ng/ml (0.25 mg/kg), and 39.4 ± 14.3 ng/ml (0.4 mg/kg). Subcutaneous Tmax (h) values for SC dosing were 0.36 ± 0.21 (0.1 mg/kg), 0.31 ± 0.17 (0.25 mg/kg), and 0.4 ± 0.13 (0.4 mg/kg). Intramuscular bioavailability values were 153.77 ± 12.60% (0.4 mg/kg), 104.8 ± 25.12% (0.25 mg/kg), and 100.7 ± 29.57% (0.1 mg/kg). Subcutaneous bioavailability values were 130.58 ± 19.07% (0.4 mg/kg), 116.6 ± 27.03% (0.25 mg/kg), and 111.6 ± 23.24% (0.1 mg/kg). No adverse effects were observed. Assuming plasma concentration required to induce analgesia is 16 ± 9 ng/ml in goats, as demonstrated in humans, it is suggested to administer morphine intramuscularly at 0.4 mg/kg every 3-4 h or SC every 2-3 h. This is a speculative conclusion therefore further studies evaluating pharmacodynamics and plasma analgesic threshold in goats is recommended.

Effects of morphine on histamine release from two cell lines of canine mast cell tumor and on plasma histamine concentrations in dogs with cutaneous mast cell tumor

OBJECTIVE

To determine the effects of morphine on histamine release from 2 canine mast cell tumor (MCT) cell lines and on plasma histamine concentrations in dogs with cutaneous MCTs.

ANIMALS

10 dogs with cutaneous MCT and 10 dogs with soft tissue sarcoma (STS).

PROCEDURES

The study consisted of 2 phases. First, 2 canine MCT cell lines were exposed to 3 pharmacologically relevant morphine concentrations, and histamine concentrations were determined by an ELISA. Second, dogs with MCT or STS received 0.5 mg of morphine/kg, IM, before surgery for tumor excision. Clinical signs, respiratory rate, heart rate, arterial blood pressure, rectal temperature, and plasma histamine concentrations were recorded before and 5, 15, 30, and 60 minutes after morphine administration but prior to surgery. Data were compared by use of a 2-way ANOVA with the Sidak multiple comparisons test.

RESULTS

In the first phase, canine MCT cell lines did not release histamine when exposed to pharmacologically relevant morphine concentrations. In the second phase, no differences were noted for heart rate, arterial blood pressure, and rectal temperature between MCT and STS groups. Plasma histamine concentrations did not significantly differ over time within groups and between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

No significant changes in histamine concentrations were noted for both in vitro and in vivo study phases, and no hemodynamic changes were noted for the in vivo study phase. These preliminary results suggested that morphine may be used safely in some dogs with MCT.

Effect of Intravenous Morphine Injection on Neurological Examination of Dogs With Thoracolumbar Intervertebral Disk Extrusion

Objectives: We aimed to determine the effect of intravenous morphine injection on the modified Frankel scores of dogs with thoracolumbar intervertebral disk extrusion (IVDE). Methods: This was a prospective, blinded, randomized, and placebo-controlled study. We included dogs with a presumptive diagnosis of thoracolumbar IVDE that did not undergo analgesic, anti-inflammatory, or sedative treatment within the last 12 h. A neurological examination was performed and the deficits were graded using the modified Frankel score (MFS). Subsequently, each dog was randomly allocated to receive an intravenous injection of either morphine or placebo. After 30 min, the dogs were re-evaluated by the same veterinary officer who was blinded to the contents of the injections. Dogs were included in the study if IVDE was ultimately confirmed by surgery within one week of initial presentation. Results: Among the 79 dogs initially enrolled, 62 dogs met the inclusion criteria. Among them, thirty-two dogs received intravenous morphine injections and there was no difference between the pre- and post-injection modified Frankel scores. Thirty dogs received an intravenous placebo injection. One dog had a worsening of the MFS by one grade in the post-injection examination. Clinical Significance: In dogs with thoracolumbar intervertebral disk extrusion, an intravenous injection of morphine does not affect the modified Frankel score after 30 min compared with the pre-injection value. These findings support the use of an analgesic morphine dose if the neurological examination can be performed 30 min or later after the injection.

Evaluation of nalbuphine, butorphanol and morphine in dogs during ovariohysterectomy and on early postoperative pain

OBJECTIVE

To evaluate the effects of nalbuphine, butorphanol and morphine combined with acepromazine on intraoperative and early postoperative pain management in dogs anesthetized for ovariohysterectomy.

STUDY DESIGN

Prospective, randomized blinded clinical study.

ANIMALS

A total of 48 healthy female dogs of different breeds, aged 1-6 years, weighing (mean ± standard deviation) 14.5 ± 4.8 kg.

METHODS

Dogs were randomly assigned into four groups to be intravenously administered nalbuphine (0.5 mg kg^-1; group N0.5), nalbuphine (1.0 mg kg^-1; group N1.0), butorphanol (0.4 mg kg^-1; group B0.4) or morphine (0.2 mg kg^-1; group M0.2) combined with acepromazine (0.02 mg kg^-1) prior to propofol and isoflurane for anesthesia. Heart rate (HR), respiratory rate, systolic arterial pressure and rectal temperature (RT) were recorded at time points during anesthesia. A dynamic interactive visual analog scale applied in three phases (DIVAS I, II and III) and the modified Glasgow composite measure pain scale were used to assess pain before premedication and 1, 2, 3, 4, 5 and 6 hours after extubation. Administration of rescue analgesia was recorded.

RESULTS

At the left ovarian pedicle ligation, HR was higher in N1.0 than in B0.4 (p = 0.020). RT decreased significantly by the end of surgery in N0.5 (p = 0.043) and B0.4 (p = 0.010). Rescue analgesia was administered postoperatively over 6 hours to eight, seven, nine and 10 dogs in N0.5, N1.0, B0.4 and M0.2, respectively (p = 0.57). DIVAS II was higher in B0.4 than in N1.0 at 2 and 3 hours (p = 0.038 and p = 0.002, respectively) and N0.5 at 3 hours (p = 0.003).

CONCLUSIONS AND CLINICAL RELEVANCE

At the doses used, all premedication protocols provided insufficient intraoperative analgesia, with minimal clinical differences between groups. No premedication provided satisfactory analgesia in the first 6 hours postoperatively.

Comparison of the effects on lameness of orally administered acetaminophen-codeine and carprofen in dogs with experimentally induced synovitis

OBJECTIVE

To compare the ability of acetaminophen-codeine (AC; 15.5 to 18.5 mg/kg and 1.6 to 2.0 mg/kg, respectively) or carprofen (4.2 to 4.5 mg/kg) administered PO to attenuate experimentally induced lameness in dogs.

ANIMALS

7 purpose-bred dogs.

PROCEDURES

A blinded crossover study was performed. Dogs were randomly assigned to receive AC or carprofen treatment first and then the alternate treatment a minimum of 21 days later. Synovitis was induced in 1 stifle joint during each treatment by intra-articular injection of sodium urate (SU). Ground reaction forces were assessed, and clinical lameness was scored at baseline (before lameness induction) and 3, 6, 9, 12, 24, 36, and 48 hours after SU injection. Plasma concentrations of acetaminophen, carprofen, codeine, and morphine were measured at various points. Data were compared between and within treatments by repeated-measures ANOVA.

RESULTS

During AC treatment, dogs had significantly higher lameness scores than during carprofen treatment at 3, 6, and 9 hours after SU injection. Peak vertical force and vertical impulse during AC treatment were significantly lower than values during carprofen treatment at 3, 6, and 9 hours. Plasma concentrations of carprofen (R)- and (S)-enantiomers ranged from 2.5 to 19.2 μg/mL and 4.6 to 25.0 μg/mL, respectively, over a 24-hour period. Plasma acetaminophen concentrations ranged from 0.14 to 4.6 μg/mL and codeine concentrations from 7.0 to 26.8 ng/mL, whereas plasma morphine concentrations ranged from 4.0 to 58.6 ng/mL.

CONCLUSIONS AND CLINICAL RELEVANCE

Carprofen as administered was more effective than AC at attenuating SU-induced lameness in dogs.

Analgesic Effect of Morphine Added to Bupivacaine in Serratus Anterior Plane Block Following Modified Radical Mastectomy. Only a Local Effect? Randomized Clinical Trial

Background

Serratus anterior plane (SAP) block, a novel regional anesthetic procedure, involves the anterolateral chest wall. Opioid receptors have been found on peripheral nerve terminals, so morphine may have a local action.

Objective

This work aimed at exploring the analgesic efficacy of morphine added to bupivacaine in SAPB in patients for whom modified radical mastectomy was conducted and whether it is a mere local effect.

Methods

Forty female patients were planned to have modified radical mastectomy participated in the study. Patients were randomly divided into two groups; Control group (C): received ultrasound-guided serratus anterior plane block with 20 mL of bupivacaine hydrochloride 0.25%; Morphine group (M): received the same in addition to 10 mg morphine sulfate. Intra- and post-operative blood samples were taken for the assessment of morphine serum levels. All patients were assessed for VAS scores during rest and movement (VAS-R and VAS-M). Time to the first request and the total amount of the rescue analgesia were recorded.

Results

In group M, Morphine was not detected in the plasma of all patients. Both VAS-R and VAS-M were significantly higher in group C than in group M (P<0.001) and (P≤0.003), respectively. Time to the first request of rescue analgesia was 8.5 h in group C compared to 20 h in group M (P=0.005) with a median dose of acetaminophen consumption of 2 g in group C compared to 1 g in group M (P=0.006).

Conclusion

Ten mg of morphine, when added to bupivacaine in SAPB, improved postoperative analgesia in patients to whom modified radical mastectomy was conducted. This effect seems to be attributed merely to local mechanisms.

Registration

The registration number of this study is NCT02962024 at www.clinicaltrial.gov.

Immunomodulatory Effects of Surgery, Pain, and Opioids in Cancer Patients

Surgery is the mainstay of therapy for canine and human solid cancers. Alarmingly, evidence suggests that the process of surgery may exacerbate metastasis and accelerate the kinetics of cancer progression. Understanding the mechanisms by which cancer progression is accelerated as a result of surgery may provide pharmacologic interventions. This review discusses surgery-induced cancer progression. It focuses on immunomodulatory properties of anesthesia and opioids and evidence that studies evaluating the role of opioids in tumor progression are indicated. It concludes by discussing why companion animals with spontaneously arising cancer are an ideal model for clinical trials to investigate this phenomenon.

Evaluation of 25% Poloxamer As a Slow Release Carrier for Morphine in a Rat Model

The objectives of this study were to evaluate poloxamer as a slow release carrier for morphine (M) and potential tissue irritation after subcutaneous poloxamer-morphine (PM) injection in a rat model. Based on the result of a previous in vitro work, 25% poloxamer, with and without morphine, and saline were administered in 14 rats' flanks. Blood for morphine concentrations was automatically sampled at multiple preprogrammed time points using the Culex™ unit for 48 h. Skin tissues from the injection sites were harvested and evaluated for histopathological changes. Following M or PM administration, it was determined that the half-life (t_1/2) was significantly longer in the PM (5.5 ± 7.2 h) than M (0.7 ± 0.8 h) indicated a slow dissolution of poloxamer with morphine. The t_max was within 15 min and C_max was approximately three times higher with M than with PM, reaching 716.8 (±153.7 ng/ml) of plasma morphine concentrations. There was no significant difference in total area under the curve and clearance of M versus PM. Histology inflammatory scores were similar between M, PM, and poloxamer but were significantly higher than saline control. We concluded that 25% poloxamer was capable of increasing the t_1/2 of morphine, without a significant tissue irritation.

Minimum alveolar concentration: Key concepts and a review of its pharmacological reduction in dogs. Part 2

OBJECTIVE

To outline the major components of the minimum alveolar concentration (MAC) and review the literature regarding pharmacological manipulation of the MAC of halothane, isoflurane, sevoflurane, enflurane, and desflurane in dogs. The pharmacological agents included are alpha-2 agonists, benzodiazepines, propofol, opioids, lidocaine, acepromazine, non-steroidal anti-inflammatory agents (NSAIDs), maropitant, and NMDA antagonists. Part 2 of this review will focus on the effect of opioids, lidocaine, NSAIDs, maropitant, acepromazine, and NMDA antagonists on MAC.

DATABASES USED

PubMed, Google Scholar, CAB Abstracts. Search terms used: minimum alveolar concentration, MAC, dog, canine, inhaled anesthetic potency, isoflurane, sevoflurane, desflurane, enflurane, and halothane.

CONCLUSIONS

Opioids, lidocaine, NSAIDs, maropitant, acepromazine, and NMDA antagonists have been shown to reduce the MAC of inhaled anesthetics in dogs and allow for clinically important decreases in inhalant anesthetic use. Thus, the use of these agents potentially decrease the adverse cardiovascular and pulmonary effects associated with the use of high concentrations of inhaled anesthetics.

Catestatin, vasostatin, cortisol, and pain assessments in dogs suffering from traumatic bone fractures

Background

Traumatic bone fractures cause moderate to severe pain, which needs to be minimized for optimal recovery and animal welfare, illustrating the need for reliable objective pain biomarkers for use in a clinical setting. The objectives of this study were to investigate catestatin (CST) and vasostatin (VS) concentrations as two new potential biomarkers, and cortisol concentrations, scores of the short form of the Glasgow composite measure pain scale (CMPS-SF), and visual analog scale (VAS) in dogs suffering from traumatic bone fractures before and after morphine administration in comparison with healthy dogs.

Methods

Fourteen dogs with hind limb or pelvic fractures and thirty healthy dogs were included. Dogs with fractures were divided into four groups according to analgesia received before participation. Physical examination, CMPS-SF, pain and stress behavior VAS scores were recorded in all dogs. Saliva and blood were collected once in healthy dogs and in dogs with fractures before and 35–70 min after morphine administration. Blood samples were analyzed for CST, VS, and cortisol. Saliva volumes, however, were insufficient for analysis.

Results

Catestatin and cortisol concentrations, and CMPS-SF, and VAS scores differed significantly between dogs with fractures prior to morphine administration and healthy dogs. After morphine administration, dogs with fractures had significantly decreased CMPS-SF and VAS scores and, compared to healthy dogs, CST concentrations, CMPS-SF, and VAS scores still differed significantly. However, CST concentrations remained largely within the normal range. Absolute delta values for CST significantly correlated with delta values for CMPS-SF. Catestatin and cortisol did not differ significantly before and after morphine administration. Vasostatin concentrations did not differ significantly between groups.

Conclusions

Catestatin and cortisol concentrations, CMPS-SF, and VAS scores differed significantly in the dogs with traumatic bone fractures compared to the healthy dogs. Morphine treatment partially relieved pain and stress according to the subjective but not according to the objective assessments performed. However, because of the large degree of overlap with normal values, our results suggest that plasma CST concentrations have a limited potential as a clinically useful biomarker for pain-induced stress.

Changes in the Welfare of an Injured Working Farm Dog Assessed Using the Five Domains Model

Simple Summary

The Five Domains Model is now increasingly used to assess the welfare status of a wide range of species in markedly different circumstances. Particular strengths are that the Model facilitates structured, systematic and comprehensive evaluations of animals’ negative and positive mental experiences, the overall balance of which underlies their welfare status or quality of life. Importantly, the Model also clarifies the specific internal and external factors that give rise to those experiences. The welfare evaluation published here is the first to use the most up-to-date version of the Model, and stands as a detailed example that may assist others undertaking such welfare evaluations in other species and contexts. Moreover, it is the first such evaluation of a companion animal. It employs a fictitious scenario involving a working farm dog before, during and after it sustains a serious hind leg injury requiring amputation and its subsequent rehoming as a pet. A wide range of negative and positive experiences are graded, interactions between them are revealed, and the balance between negative and positive states at different stages of the scenario is described. Such Model evaluations can highlight current practices that merit re-evaluation. More generally, when major welfare issues are identified, use of the Model could enhance expert witness participation in related prosecutions by highlighting scientifically supported connections between indicative physical/functional states and behaviours and their associated negative experiences in ill-treated animals. Five Domains Model evaluations can also facilitate quality of life assessments and end-of-life decisions.

Abstract

The present structured, systematic and comprehensive welfare evaluation of an injured working farm dog using the Five Domains Model is of interest in its own right. It is also an example for others wanting to apply the Model to welfare evaluations in different species and contexts. Six stages of a fictitious scenario involving the dog are considered: (1) its on-farm circumstances before one hind leg is injured; (2) its entanglement in barbed wire, cutting it free and transporting it to a veterinary clinic; (3) the initial veterinary examination and overnight stay; (4) amputation of the limb and immediate post-operative recovery; (5) its first four weeks after rehoming to a lifestyle block; and (6) its subsequent life as an amputee and pet. Not all features of the scenario represent average-to-good practice; indeed, some have been selected to indicate poor practice. It is shown how the Model can draw attention to areas of animal welfare concern and, importantly, to how welfare enhancement may be impeded or facilitated. Also illustrated is how the welfare implications of a sequence of events can be traced and evaluated, and, in relation to specific situations, how the degrees of welfare compromise and enhancement may be graded. In addition, the choice of a companion animal, contrasting its welfare status as a working dog and pet, and considering its treatment in a veterinary clinical setting, help to highlight various welfare impacts of some practices. By focussing attention on welfare problems, the Model can guide the implementation of remedies, including ways of promoting positive welfare states. Finally, wider applications of the Five Domains Model are noted: by enabling both negative and positive welfare-relevant experiences to be graded, the Model can be applied to quality of life assessments and end-of-life decisions and, with particular regard to negative experiences, the Model can also help to strengthen expert witness testimony during prosecutions for serious ill treatment of animals.

Epidural levobupivacaine alone or combined with different morphine doses in bitches under continuous propofol infusion

The aim of this study was to assess the cardiopulmonary, analgesic, adverse effects, serum concentration of cortisol and plasma levels of levobupivacaine and morphine in bitches undergoing propofol anesthesia and epidural analgesia with levobupivacaine alone or combined with morphine. This was a randomized 'blinded' prospective clinical study using 32 adult bitches weighing 9.8±4.1kg that were admitted for elective ovariohysterectomy. Twenty minutes after administration of acepromazine and midazolam, anesthesia was induced with propofol (4mg kg-1) and maintained by a continuous rate infusion (CRI). Each animal was randomly assigned to one of four epidural groups: GL = levobupivacaine alone (0.33mg kg-1); GLM0.1 = levobupivacaine and morphine (0.1mg kg-1); GLM0.15 = levobupivacaine and morphine (0.15mg kg-1); and GLM0.2 = levobupivacaine and morphine (0.2mg kg-1). Variables obtained during anesthesia were heart rate, respiratory rate, systolic, mean and diastolic arterial blood pressures, oxyhemoglobin saturation, inspired oxygen fraction, end-tidal carbon dioxide tension, blood gases, serum cortisol, and plasma levels of levobupivacaine and morphine. The onset and duration times of the blockade were recorded. Arterial pressures were significantly increased in all groups at the times of ovarian pedicle clamping. There was a decrease in pH, together with an increase in both PaO2and PaCO2 over time. Serum cortisol levels were increased in TESu compared to TB, T30 and TR. Limb spasticity, muscle tremors, opisthotonos and diarrhea were observed in some animals during propofol infusion and ceased with the end of CRI. Reactions happened at different moments and lasted for different periods of time in each individual. Epidural with levobupivacaine alone or combined with morphine allowed for ovariohysterectomy to be performed under low propofol infusion rates, with minimal changes in cardiovascular variables and in serum cortisol levels. Adverse effects were observed in very few animals in each group.

Applying Biopharmaceutical Classification System (BCS) Criteria to Predict Oral Absorption of Drugs in Dogs: Challenges and Pitfalls

The Biopharmaceutical Classification System (BCS) has been a prognostic tool for assessing the potential effects of formulation on the human drug oral bioavailability. When used in conjunction with in vitro dissolution tests, the BCS can support the prediction of in vivo product performance and the development of mechanistic models that support formulation assessments through the generation of "what if" scenarios. To date, the applicability of existing human BCS criteria has not been evaluated in dogs, thereby limiting its use in canine drug development. Therefore, we examined 50 drugs for which absolute bioavailability (F) was available both in dogs and humans. The drugs were also evaluated for any potential association between solubility (calculated from the dose number, Do) or lipophilicity (LogP) and F in dogs. In humans, solubility is determined in 250 mL of fluid. However, the appropriate volume for classifying drug solubility in dogs has not been established. In this analysis, the estimated volume of a water flush administered to fasted dogs (6 mL) and a volume of 250 mL scaled to a Beagle dog (35 mL) were examined. In addition, in humans, a Do value greater than 1.0 is used to define a compound as highly soluble and a LogP value greater than 1.72 as high permeability. These same criteria were applied for defining highly soluble and highly permeable in dogs. Whether using 35 or 6 mL to determine Do, the canine solubility classification remained unchanged for all but seven compounds. There were no clear associations between a drug's F in dogs and humans or between the canine value of F and either its human BCS classification, its LogP value, or the canine Do estimate. There was a tendency for those drugs with canine values of F equal to or greater than 80% to have LogP values equal to or greater than 1.0. Exceptions to this observation tended to be those compounds known to be absorbed via mechanisms other than passive diffusion (e.g., via transporters or paracellular transporters). Although there are limitations to the approach used in this study, the results of our assessment strongly suggest that the human BCS classification system requires substantial modification before it can be reliably applied to dogs.

Effects of ropivacaine combined with morphine at 0.15 and 0.2 mg kg(-1) in bitches undergoing epidural anesthesia

PURPOSE

To investigate cardiorespiratory effects and serum concentration of ropivacaine combined with morphine at different doses.

METHODS

Sixteen healthy adult female dogs weighting 9.8 ± 4.1 kg were included in the study. Twenty minutes after being premedicated with acepromazine and midazolam, the animals were randomly assigned to receive an epidural injection according to each group: RM0.15 = ropivacaine + morphine (0.15 mg kg(-1)) and RM0.2 = ropivacaine + morphine (0.2 mg kg(-1)). Variables recorded consisted of: heart rate and cardiac rhythm, respiratory rate, oxyhemoglobin saturation, inspired oxygen fraction, end-tidal carbon dioxide tension, systolic, mean and diastolic arterial pressures, serum cortisol, plasma ropivacaine and morphine.

RESULTS

SAP, MAP and DAP were significantly increased at TPR in RM0.15 but returned to normal values at the end of the procedure. Arterial pH was decreased in T30 and TESu in both groups and also returned to acceptable ranges at TR. Both PaO2 and PaCO2 were increased along the duration period of the epidural blockade (T30 and TESu) and returned to acceptable values at TR. Serum cortisol was lower at TB, T30 and TR when compared to TESu.

CONCLUSION

The procedures were performed safely and minimal changes in cardiovascular and respiratory variables.

Adjunctive, pain-modifying, analgesic drugs

Outside the realm of nonsteroidal antiinflammatory drug(NSAID) and opioid exist a broad range of medications that exert an analgesic effect, or otherwise modify and protect against pain, by manipulating various targets along the nociceptive pathway. Strength of evidence for dogs and cats can vary widely, and this article will review the available literature that may guide clinical usage in these species.

Veterinarians' attitudes to chronic pain in dogs

Veterinary surgeons in the UK were invited to complete an internet survey concerning their attitudes to chronic pain in dogs. UK veterinary surgeons numbering 215 completed surveys in full along with 48 worldwide specialists in anaesthesia and 37 worldwide specialists in oncology. Osteoarthritis, dental and aural disease, vertebral and spinal cord conditions, neoplasia and skin conditions were considered important causes of chronic pain in dogs. UK practitioners used significantly fewer classes of analgesic drugs regularly than either category of specialist. The major barriers to adequate treatment of chronic pain were reported as difficulties with pain assessment, expense of drugs, and difficulties with owner compliance. Illustrations of six common neoplastic conditions were used and scored for pain according to prior experience by practitioners. All six conditions were consistently described as involving some degree of pain with primary bone tumour and oral tumour, causing severe pain and moderate to severe pain, respectively. Years since graduation and specialist status affected the pain scores attributed to the conditions. There was a significant correlation between the pain score attributed to the illustrated condition, and the tendency to administer analgesia.

The safety and effectiveness of a long-acting transdermal fentanyl solution compared with oxymorphone for the control of postoperative pain in dogs: a randomized, multicentered clinical study

A prospective, double-blinded, positive-controlled, multicenter, noninferiority study was conducted to evaluate the safety and effectiveness of transdermal fentanyl solution (TFS) compared with oxymorphone for the control of postoperative pain in dogs. Five hundred and two (502) client-owned dogs were assigned to a single dose of TFS (2.7 mg/kg) applied 2–4 h prior to surgery or oxymorphone hydrochloride (0.22 mg/kg) administered subcutaneously 2–4 h prior to surgery and q6h through 90 h. Pain was evaluated over 4 days by blinded observers using a modified Glasgow composite pain scale, and the a priori criteria for treatment failure was a pain score ≥8 or adverse event necessitating withdrawal. Four TFS- and eight oxymorphone-treated dogs were withdrawn due to lack of pain control. Eighteen oxymorphone-treated, but no TFS-treated dogs were withdrawn due to severe adverse events. The one-sided upper 95% confidence interval of the difference between TFS and oxymorphone treatment failure rates was −5.3%. Adverse events associated with oxymorphone were greater in number and severity compared with TFS. It was concluded that a single administration of TFS was safe and noninferior to repeated injections of oxymorphone for the control of postoperative pain over 4 days at the dose rates of both formulations used in this study.

Pharmacokinetics of ammonium sulfate gradient loaded liposome-encapsulated oxymorphone and hydromorphone in healthy dogs

OBJECTIVE

To evaluate the pharmacokinetics, in dogs, of liposome-encapsulated oxymorphone and hydromorphone made by the ammonium sulfate gradient loading technique (ASG).

ANIMALS

Four healthy purpose-bred Beagles aged 9.5 ± 3.2 months and weighing 13.4 ± 2.3 kg.

STUDY DESIGN

Randomized cross-over design.

METHODS

Each dog was given either 4.0 mg kg(-1) of ASG-oxymorphone or 8.0 mg kg(-1) of ASG-hydromorphone SC on separate occasions with a 3-month washout period. Blood was collected at baseline and at serial time points up to 1032 hours (43 days) after injection for determination of serum opioid concentrations. Serum opioid concentrations were measured with HPLC-MS and pharmacokinetic parameters were calculated using commercial software and non-compartmental methods.

RESULTS

Serum concentrations of oxymorphone remained above the limit of quantification for 21 days, while those for hydromorphone remained above the limit of quantification for 29 days. Cmax for ASG-oxymorphone was 7.5 ng mL(-1) ; Cmax for ASG-hydromorphone was 5.7 ng mL(-1) .

CONCLUSIONS AND CLINICAL RELEVANCE

Oxymorphone and hydromorphone, when encapsulated into liposomes using the ammonium sulfate gradient loading technique, result in measureable serum concentrations for between 3 to 4 weeks. This formulation may have promise in the convenient use of opioids for clinical treatment of chronically painful conditions in dogs.

Pharmacokinetics of hydrocodone and hydromorphone after oral hydrocodone in healthy Greyhound dogs

The purpose of this study was to determine the pharmacokinetics of hydrocodone and its active metabolite hydromorphone in six healthy Greyhound dogs. Hydrocodone bitartrate was administered at a targeted dose of 0.5 mg/kg PO. Plasma concentrations of hydrocodone and hydromorphone were determined by liquid chromatography triple quadrupole mass spectrometry. The mean hydrocodone CMAX was 11.73 ng/mL at 0.74 h with a terminal half-life of 1.60 h. The mean hydromorphone CMAX was 5.2 ng/mL at 1.37 h with a terminal half-life of 3.07 h. Mean plasma hydromorphone concentrations exceeded 2 ng/mL from 0.5 to 8 h after hydrocodone administration. Further studies assessing the antinociceptive effects of oral hydrocodone are needed.

Cardiovascular effects of a proprietary l-methadone/fenpipramide combination (Polamivet) alone and in addition to acepromazine in healthy Beagle dogs

OBJECTIVE

To determine the cardiovascular effects of a proprietary l-methadone/fenpipramide combination (Polamivet) alone and in addition to acepromazine in dogs.

STUDY DESIGN

Prospective, randomized, experimental crossover study.

ANIMALS

Five adult healthy Beagle dogs (one male and four females, weighing 12.8-16.4 kg).

METHODS

Dogs were instrumented for haemodynamic measurements whilst anaesthetized with isoflurane. Three hours after recovery dogs received 0.025 mg kg(-1) acepromazine (AP) or saline (SP) IM followed by 0.5 mg kg(-1) L-methadone/ 0.025 mg kg(-1) fenpipramide IV after 30 minutes. Cardiac output using thermodilution, heart rate, mean arterial pressure (MAP), central venous pressure (CVP), mean pulmonary artery pressure (MPAP), pulmonary artery occlusion pressure (PAOP), haemoglobin concentration, arterial and mixed-venous blood gas analysis were measured and sedation evaluated at baseline (BL), 30 minutes after acepromazine or saline IM (A/S), 5 minutes after L-methadone/fenpipramide IV application (35), every 15 minutes for 1 hour (50, 65, 80, 95 minutes) and every hour until baseline cardiac output was regained. Standard cardiovascular parameters were calculated. Data were analyzed by repeated measures anova and paired t-tests with p < 0.05 considered significant.

RESULTS

Baseline measurements did not differ. Cardiac index decreased after acepromazine administration in treatment AP (p = 0.027), but was not significantly influenced after l-methadone/fenpipramide injection in either treatment. In both treatments heart rate did not change significantly over time. Stroke volume index increased after A/S in both treatments (p = 0.049). Systemic vascular resistance index, MAP, CVP, MPAP, and pulmonary vascular resistance index did not change significantly after either treatment and did not differ between treatments. Dogs were deeply sedated in both treatments with a longer duration in treatment AP.

CONCLUSIONS AND CLINICAL RELEVANCE

In healthy dogs the dose of l-methadone/fenpipramide used in this study alone and in combination with acepromazine induced deep sedation without significant cardiovascular changes.

Correlation between in silico physicochemical characteristics of drugs and their mean residence time in human and dog

The correlation between 52 physicochemical parameters and mean residence time (MRT) for 27 drugs used in human and dog were investigated. The physicochemical parameter values calculated provided a basis for deriving a series of arithmetic expressions, which were used to build a mathematical model describing the relationship between them and the MRT values. From the entire set of analyzed parameters, a subset of 14 was identified that contributed to the derivation of an arithmetic expression: Log(PSA - WPSA + ACID) x [XlogP - (LogKp - EAxLn(Caco2 + AMINE + SAF))] + (AMIDE + IP - FG) - Ln(MW + PISA) the value of which is highly correlated with the MRT value in dogs (P < .001) and allowed prediction of the MRT predicted (MRT(pred)). In humans, no correlation was found that allowed the calculation of MRT(pred). These results indicate that predicting the pharmacokinetics of any specific drug for humans based on pharmacokinetic data obtained in the dog should be undertaken with knowledge of the inherent limitations.

The effects of concurrent administration of cytochrome P-450 inhibitors on the pharmacokinetics of oral methadone in healthy dogs

OBJECTIVE

The objective was to examine the effects of inhibiting cytochrome P450 (CYP) on the pharmacokinetics of oral methadone in dogs.

STUDY DESIGN

Prospective non-randomized experimental trial.

ANIMALS

Six healthy Greyhounds (three male and three female).

METHODS

The study was divided into two phases. Oral methadone (mean = 2.1 mg kg(-1) PO) was administered as whole tablets in Phase 1. In Phase 2 oral methadone (2.1 mg kg(-1) PO) was administered concurrently with ketoconazole (13.0 mg kg(-1) PO q 24 hours), chloramphenicol (48.7 mg kg(-1) PO q 12 hours), fluoxetine (1.3 mg kg(-1) PO q 24 hours), and trimethoprim (6.5 mg kg(-1) PO q 24 hours). Blood was obtained for analysis of methadone plasma concentrations by liquid chromatography with mass spectrometry. The maximum plasma concentration (C(max)), time to C(max) (T(max)), and the area under the curve from time 0 to the last measurable time point above the limit of quantification of the analytical assay (AUC(0-LAST)) were compared statistically.

RESULTS

The C(max) of methadone was significantly different (p=0.016) for Phase 1 (5.5 ng mL(-1)) and Phase 2 (171.9 ng mL(-1)). The AUC(0-LAST) was also significantly different (p=0.004) for Phase 1 (13.1 hour ng mL(-1)) and Phase 2 (3075.2 hour ng mL(-1)).

CONCLUSION AND CLINICAL RELEVANCE

Concurrent administration of CYP inhibitors with methadone significantly increased the area under the curve and plasma concentrations of methadone after oral administration to dogs. Further studies are needed assessing more clinically relevant combinations of methadone and CYP inhibitors.

Clinical interpretation of pharmacokinetic and pharmacodynamic data in zoologic companion animal species

The treatment and prevention of pain in zoologic companion animals is difficult because of the lack of data available on the safety and efficacy of analgesics. Pharmacokinetic (PK)-pharmacodynamic (PD) studies integrate changes in drug concentrations and changes in the drug's effect. All experimental studies assessing the PDs of analgesics have limitations in animals, but the data provided by experimental studies are valuable in designing dosages. Placebo-controlled, randomized, and blinded clinical trials provide the best PK and PD data, but are rarely performed in major veterinary species because of the number of animals required for the study, lack of preliminary PK and PD data in a given species, species-specific differences in PK and PD, and ethical and toxicologic concerns. The usefulness and limitations as well as considerations for interpreting PK, PD, and controlled clinical studies are discussed. An example of allometric analysis of buprenorphine in mammals is also included.

Pharmacokinetics of acetaminophen, codeine, and the codeine metabolites morphine and codeine-6-glucuronide in healthy Greyhound dogs

The purpose of this study was to determine the pharmacokinetics of codeine and the active metabolites morphine and codeine-6-glucuronide after i.v. codeine administration and the pharmacokinetics of acetaminophen (APAP), codeine, morphine, and codeine-6-glucuronide after oral administration of combination product containing acetaminophen and codeine to dogs. Six healthy Greyhound dogs were administered 0.734 mg/kg codeine i.v. and acetaminophen (10.46 mg/kg mean dose) with codeine (1.43 mg/kg mean dose) orally. Blood samples were collected at predetermined time points for the determination of codeine, morphine, and codeine-6-glucuronide plasma concentrations by LC/MS and acetaminophen by HPLC with UV detection. Codeine was rapidly eliminated after i.v. administration (T(1/2) = 1.22 h; clearance = 29.94 mL/min/kg; volume of distribution = 3.17 L/kg) with negligible amounts of morphine present, but large amounts of codeine-6-glucuronide (C(max) = 735.75 ng/mL) were detected. The oral bioavailability of codeine was 4%, morphine concentrations were negligible, but large amounts of codeine-6-glucuronide (C(max) = 1952.86 ng/mL) were detected suggesting substantial first pass metabolism. Acetaminophen was rapidly absorbed (C(max) = 6.74 microg/mL; T(max) = 0.85 h) and eliminated (T(1/2) = 0.96 h). In conclusion, the pharmacokinetics of codeine was similar to other opioids in dogs with a short half-life, rapid clearance, large volume of distribution, and poor oral bioavailability. High concentrations of codeine-6-glucuronide were detected after i.v. and oral administration.

Effect of morphine on the bispectral index during isoflurane anesthesia in dogs

OBJECTIVE

To assess the effect of morphine on the bispectral index (BIS) in dogs during isoflurane anesthesia maintained at a constant end-tidal concentration.

STUDY DESIGN

Prospective, randomized, experimental trial.

ANIMALS

Eight adult Beagle dogs, weighing between 7.1 and 9.8 kg.

METHODS

Anesthesia was induced with isoflurane via a face mask. Dog's tracheas were intubated and anesthesia maintained with isoflurane at a constant end-tidal concentration (e'Iso) of 1.81% for a 30-minute equilibration period. Pulmonary ventilation was controlled to normocapnia. After equilibration, baseline values were recorded prior to intravenous administration of morphine sulfate (0.5 mg kg(-1)) (MT) or an equal volume of saline (CT). Measurements for heart rate, systolic, diastolic and mean arterial pressure (SAP, DAP and MAP) were recorded at 10, 20, 30, 45, 60, 75, 90, 105 and 120 minutes after treatment. Bispectral index was recorded every 10 seconds for 3 minutes for each time measurement. Venous blood samples were collected at baseline, 10, 20, 30, 45, 60 and 120 minutes for determination of morphine serum concentrations. Anesthesia was discontinued after the last measurement and dogs were allowed to recover.

RESULTS

Baseline BIS for MT and CT at 1.81%e'Iso were 63 +/- 10 and 58 +/- 9, respectively. Bispectral index in MT was 4-8% lower at 20, 75, 90 and 105 minutes compared with CT. There were no differences in BIS between baseline and any subsequent measurement within either MT or CT. Heart rate, SAP, MAP, and DAP decreased after morphine administration.

CONCLUSION AND CLINICAL RELEVANCE

Intravenous administration of 0.5 mg kg(-1) morphine sulfate did not cause clinically significant changes in the BIS of unstimulated dogs during isoflurane anesthesia at an e'Iso of 1.81%.