Antinociceptive efficacy and plasma concentrations of transdermal buprenorphine in dogs

Plasma concentrations of buprenorphine administered via matrix-type transdermal patches applied at three different anatomical locations in healthy adult horses

Background

Anatomical location-dependent differences in transdermal opioid penetration are well described in human patients. Although this has been investigated in horses with fentanyl, there is no literature available on location-dependent plasma buprenorphine concentrations when administered as a transdermal matrix-type patch.

Objective

This study aims to compare the plasma concentrations achieved from the matrix-type transdermal buprenorphine patches placed at different anatomical sites (metacarpus, gaskin, and ventral tail base) in healthy adult horses.

Study design

This is a randomized experimental study with a Latin square design.

Methods

Six adult horses were given each of three treatments with a minimum 10-day washout period. For each treatment, two 20 μg h-1 matrix-type buprenorphine patches were applied to the ventral aspect of the tail base (TailTDP), metacarpus region (MetacarpusTDP), or gaskin region (GaskinTDP). Whole blood samples (for determination of buprenorphine concentration) and physiological variables were collected before (0 h) and at 0.5, 2, 4, 6, 8, 10, 12, 16, 24, 32, 48, 56, 72, 96 and 120 h after patches were applied. The patches were removed 96 h following placement and were analyzed for residual buprenorphine content. Buprenorphine concentrations were measured in plasma by LC-MS/MS. A mixed-effects model was used to analyze the physiological variables.

Results

Between the three treatment groups, there was no change in physiological variables across timepoints as compared to baseline and when compared to each other in a single horse and between horses (p > 0.3). When comparing all three locations, the buprenorphine uptake was observed to be more consistent with respect to measurable plasma concentrations >0.1 ng ml-1 when applied to the ventral aspect of the tail base. In the TailTDP group, the mean plasma buprenorphine concentrations were >0.1 ng ml-1 from 2 to 32 h. The highest group mean was 0.25 ng ml-1 noted at 4 h.

Conclusions

The metacarpal and gaskin regions presented more erratic and inconsistent buprenorphine uptake and plasma concentrations as compared to the ventral aspect of the tail base. Further research must be directed at investigating the optimal dose, achievable duration of analgesia, change in measurable plasma concentrations, and behavioral and systemic effects.

Evaluation of physical variables, thermal nociceptive threshold testing and pharmacokinetics during placement of transdermal buprenorphine matrix-type patch in healthy adult horses

Background

Matrix type transdermal buprenorphine patches have not been investigated in horses and may provide an effective means of providing continuous pain control for extended period and eliminating venous catheterization.

Objective

Assessment of the physiological variables (heart rate, respiratory rate, body temperature) and thermal nociceptive threshold testing, and describing the pharmacokinetic profile of transdermal buprenorphine matrix-type patch (20 μg h-1 and 40 μg h-1 dosing) in healthy adult horses.

Study design

Randomised experimental study with a Latin-square design.

Methods

Six adult healthy horses received each of the three treatments with a minimum 10 day washout period. BUP0 horses did not receive a patch (control). BUP20 horses received one patch (20 μg h-1) applied on the ventral aspect of the tail base resulting in a dose of 0.03-0.04 μg kg-1 h-1. BUP40 horses received two patches placed alongside each other (40 μg h-1) on the tail base resulting in a dose of 0.07-0.09 μg kg-1 h-1. Whole blood samples (for determination of buprenorphine concentration), physiological variables and thermal threshold testing were performed before (0 h) and at 2, 4, 8, 12, 16, 24, 32, 40, 48, 56, 64, 72, and 96 h after patch application. The patches were removed 72 h following placement and were analyzed for residual buprenorphine content.

Results

Between the three groups, there was no change in physiological variables across timepoints as compared to baseline (p > 0.1). With the higher dose, there was a significant increase in thermal thresholds from baseline values from 2 h until 48 h and these values were significantly higher than the group receiving the lower patch dose for multiple timepoints up to 40 h. 40 μg h-1 patch led to consistent measurable plasma concentrations starting at 2 h up to 96 h, with the mean plasma concentrations of > 0.1 ng/ml from 4 h to 40 h.

Conclusions

20 μg h-1 and 40 μg h-1 patch doses were well tolerated by all horses. At higher dose, plasma buprenorphine concentrations were more consistently measurable and blunted thermal thresholds for 48 h vs. 32 h with 20 μg h-1 dosing as compared to control.

Long-Acting Opioid Analgesics for Acute Pain: Pharmacokinetic Evidence Reviewed

Long-acting injectable (LAI) opioid formulations mitigate the harm profiles and management challenges associated with providing effective analgesia for animals. A single dose of a long-acting opioid analgesic can provide up to 72 h of clinically relevant pain management. Yet, few of these new drugs have been translated to products for veterinary clinics. Regulatory pathways allow accelerated drug approvals for generic and biosimilar drugs. These pathways depend on rigorous evidence for drug safety and pharmacokinetic evidence demonstrating bioequivalence between the new and the legacy drug. This report reviews the animal PK data associated with lipid and polymer-bound buprenorphine LAI formulations. Buprenorphine is a widely used veterinary opioid analgesic. Because of its safety profile and regulatory status, buprenorphine is more accessible than morphine, methadone, and fentanyl. This review of PK studies coupled with the well-established safety profile of buprenorphine suggests that the accelerated approval pathways may be available for this new family of LAI veterinary pharmaceuticals.

Pharmacokinetic Evaluation of a Novel Transdermal Ketoprofen Formulation in Healthy Dogs

Dogs undergo various surgical procedures such as castration, ovariohysterectomy, and other orthopedic procedures, which are known to cause inflammation and pain. Non-steroidal anti-inflammatory drugs (NSAIDs) are very effective analgesics for alleviating postoperative pain in veterinary medicine. Ketoprofen is currently approved in Australia and the United States for treating different painful conditions in dogs. This study evaluated the pharmacokinetic parameters of ketoprofen after intravenous (IV) and transdermal (TD) administration in healthy dogs. A novel transdermal ketoprofen (TDK) formulation containing 20% ketoprofen, dissolved in a combination of 45:45% isopropanol and Transcutol, along with 10% eucalyptus oil, was developed and evaluated for in vitro dermal permeation using Franz diffusion cells. A crossover study was then conducted to determine the pharmacokinetic parameters of the formulation in six dogs following IV ketoprofen (1 mg/kg) and TDK (10 mg/kg) administration. A liquid chromatography–mass spectrometry (LC-M/MS) method was used to measure plasma concentrations of ketoprofen over time, and a non-compartmental analysis determined the pharmacokinetic parameters. The mean terminal elimination half-life (T_½ h), AUC_0-t (µg·h/mL), and mean residence time (MRT, h) between IV and TDK groups were 4.69 ± 1.33 and 25.77 ± 22.15 h, 15.75 ± 7.72 and 8.13 ± 4.28 µg·h/mL, and 4.86 ± 1.81 and 41.63 ± 32.33 h, respectively. The calculated bioavailability (F%) was ~7%, with a lag time of 30 min to achieve effective plasma concentrations after the application of TDK.

Aspects in controlled drug delivery for topical applications in veterinary medicine

The controlled release of drugs is an appealing area of research as it provides numerous benefits in veterinary and human medicine. In this paper we attempt to analyze certain aspects related to topical drug delivery systems, their successes and failures, and their place in veterinary medicine. Some emphasis is given to the pharmaceutical aspects of the delivery systems, where the material available made it possible. Purely topical devices, such as cattle ear tags and various collars, as well as some topically administered bioavailable delivery systems are discussed. Special attention is given to hitherto under-evaluated delivery systems, such as topical varnishes. A carefully selected bibliography aims to lead the reader easily to the facts, without providing overwhelming data of varying quality. We believe that the paper may be of interest to practicing veterinarians as well as to pharmaceutical scientists working or considering practice in the area.

Automated blood sampling in canine telemetry studies: Enabling enhanced assessments of cardiovascular liabilities and safety margins

INTRODUCTION

A successful integration of automated blood sampling (ABS) into the telemetry instrumented canine cardiovascular model is presented in this study. This combined model provides an efficient means to quickly gain understanding of potential effects on key cardiovascular parameters in dog while providing a complete Pharmacokinetic/Pharmacodynamic (PK/PD) profile for discovery compounds without handling artifacts, reducing the need for a separate pharmacokinetic study.

METHODS

Male beagle dogs were chronically implanted with telemetry devices (PhysioTel™ model D70-PCTP) and vascular access ports (SPMID-GRIDAC-5NC). BASi Culex-L automated blood sampling (Bioanalytical Systems, Inc) system was used to collect blood samples at multiple time points. A series of four use cases utilizing four different test compounds and analytical endpoints are described to illustrate some of the potential applications of the technique.

RESULTS

In the four presented use cases, automated blood sampling in telemetry instrumented dogs provides simultaneous cardiovascular (heart rate, arterial blood pressure, and left ventricular pressure), electrophysiological assessment (QTc, PR, and QRS intervals), body temperature, and animal activity, while collecting multiple blood samples for drug analysis.

CONCLUSION

The combination of automated blood sampling with cardiovascular telemetry monitoring is a novel capability designed to support safety pharmacology cardiovascular assessment of discovery molecules. By combining telemetry and high-fidelity ABS, the model provides an enhanced PK/PD understanding of drug-induced hemodynamic and electrocardiographic effects of discovery compounds in conscious beagles in the same experimental session. Importantly, the model can reduce the need for a separate pharmacokinetic study (positive reduction 3R impact), reduces compound syntheses requirements, and shorten development timelines. Furthermore, implementation of this approach has also improved animal welfare by reducing the animal handling during a study, thereby reducing stress and associated data artifacts (positive refinement 3R impact).

MATERNAL AND FETAL BUPRENORPHINE PHARMACOKINETICS IN PREGNANT SHEEP DURING TRANSDERMAL PATCH DOSING: Buprenorphine pharmacokinetics in pregnant sheep

BACKGROUND

Buprenorphine is used in the opioid maintenance treatment for opioid dependent patients, including pregnant women. Despite the wide use, limited data exists on buprenorphine pharmacokinetics and fetal exposure during pregnancy. The aim of our study was to determine the buprenorphine pharmacokinetics during transdermal patch dosing to pregnant sheep and, to determine the extent of transplacental transfer of buprenorphine to the fetus.

METHODS

Pregnant sheep in late gestation (n=50) received 20, 25 or 40 µg/h of buprenorphine as a 7-day extended-release transdermal patch. Plasma samples were collected from the ewe and the fetus on days 1 - 6, and buprenorphine and norbuprenorphine concentrations were determined. During the exposure period the sheep had a surgical procedure on the second day, a recovery phase, and an experimental procedure on the sixth day. In the experiment, hypoxia was induced under anesthesia for 18 sheep to investigate if decreased fetal pH would cause ion-trapping of buprenorphine in the fetus. The fetal/maternal plasma concentration ratio was determined on the second and on the sixth exposure day at baseline and during hypoxia. Maternal pharmacokinetics were modelled with a population pharmacokinetic method using the data from this study and our previous intravenous administration study.

RESULTS

The transdermal patch provided an extended release of buprenorphine throughout the exposure period, but the release rate declined approximately 20 h after patch placement. The median fetal/maternal plasma concentration ratio was 13 - 27 % throughout the exposure period at baseline. A ratio over 100 % was observed for four sheep on the sixth exposure day (102 - 269 %). A minor increase was seen in the median fetal/maternal-ratios during maternal hypoxia. Norbuprenorphine was undetected in all plasma samples.

CONCLUSIONS

The low transplacental passage of less than one fourth of the ewe's exposure supports buprenorphine as an alternative to methadone in opioid maintenance therapy during pregnancy.

Pharmacokinetics of a high-concentration formulation of buprenorphine (Simbadol) in male dogs

OBJECTIVE

To describe the pharmacokinetics of buprenorphine in dogs following administration of a high-concentration formulation of buprenorphine.

STUDY DESIGN

Prospective, randomized, crossover study.

ANIMALS

A total of six healthy male intact Beagle dogs, aged 9-13 months and weighing 10.3 ± 1.4 kg (mean ± standard deviation).

METHODS

Dogs were randomized to be administered buprenorphine (0.12 mg kg^-1; Simbadol, 1.8 mg mL^-1) via the intravenous (lateral saphenous) or subcutaneous (dorsal interscapular) route followed by the alternative route of administration after a 14 day interval. Blood was sampled before administration and at set times up to 72 hours after injection. Plasma buprenorphine concentration was measured using liquid chromatography-tandem mass spectrometry.

RESULTS

A three-compartment model with zero or biphasic rapid and slow first-order input in (intravenous or subcutaneous data, respectively) and first-order elimination from the central compartment best fitted the data. The rapid first-order input accounted for 63% of the dosage absorption. Typical values (% interindividual variability) for the three compartment volumes were 900 (33), 2425 (not estimated) and 6360 (28) mL kg^-1. The metabolic and two distribution clearances were 25.7 (21), 107.5 (74) and 5.7 (61) mL minute^-1 kg^-1. The absorption half-life for the fast absorption phase was 8.9 minutes with a 0.7 (103) minute delay. The absorption half-life for the slow absorption phase was 347 minutes with a 226 (42) minute delay. Median (range) bioavailability calculated from noncompartmental analysis was 143 (80-239)%. Calculated terminal half-life was 963 minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

The high-concentration formulation of buprenorphine administered subcutaneously had a large volume of distribution and a rapid absorption phase followed by slower, delayed absorption. The high estimate of bioavailability should be interpreted with caution as values above 100% are most commonly related to experimental issues.

Multiple-dose pharmacokinetics and opioid effects of a novel analgesic with a deterrent to human opioid abuse (methadone-fluconazole-naltrexone) after oral administration in dogs

OBJECTIVE

To assess the pharmacokinetics and opioid effects of methadone after administration of multiple doses by means of 2 dosing regimens of methadone-fluconazole-naltrexone.

ANIMALS

12 healthy Beagles.

PROCEDURES

Dogs were randomly allocated (6 dogs/group) to receive 1 of 2 oral dosing regimens of methadone-fluconazole-naltrexone. Treatment 1 doses were administered at 0 (methadone-to-fluconazole-to-naltrexone ratio of 1:5:0.25 mg/kg), 14 (1:5:0.25), 24 (0.5:2.5:0.125), and 38 (0.5:2.5:0.125) hours. Treatment 2 doses were administered at 0 (1:5:0.25), 4 (0.5:2.5:0.125), 10 (0.5:2.5:0.125), and 24 (0.5:2.5:0.125) hours. Blood samples, rectal temperatures, and von Frey antinociceptive measurements were obtained at designated times.

RESULTS

Compared with baseline, temperatures significantly decreased for treatment 1 group dogs at 2 to ≥ 4 hours and from 16 to ≥ 50 hours (12 hours after last dose) and for treatment 2 group dogs at 2 to ≥ 36 hours (12 hours after last dose), when trough methadone concentrations were ≥ 21.3 ng/mL. Antinociception occurred after the first dose but was not maintained throughout the study. Lesions were noted in some dogs at the application site of the von Frey device. Naltrexone and β-naltrexol were sporadically detected in plasma, and naltrexone glucuronide was consistently detected.

CONCLUSIONS AND CLINICAL RELEVANCE

Opioid effects were noted after oral administration of the first dose, and data suggested that administering a second dose 6 hours later and every 12 hours thereafter was necessary to maintain opioid effects. Antinociception may have been lost because dogs became averse or hyperalgesic to the von Frey device, such that the antinociception model used here may not be robust for repeated measurements in dogs.

Buprenorphine implants: a model for expedited development and approval of new drugs

Regulations for new drug approvals require stringent safety testing and efficacy trial programs. The approval process for generic drugs, however, is significantly streamlined. Bioavailability data can substitute for new rounds of efficacy trials, thereby both decreasing time to approval and reducing the costs required for new studies. This regulatory choice has not been available when generic drugs are offered in a controlled release format such as a subcutaneous depot, transdermal patch or implant. The purpose of this review is to suggest that the approval of generic drugs in inert controlled release envelopes should be eligible for similar regulatory relief. Proof for this concept is provided by the example of the numerous controlled release buprenorphine products. Buprenorphine is a generic opioid used since the 1980s in tablet form to treat pain and to treat opioid addiction. Long-acting, inert delivery vehicles for the drug have become available for the same indications. Safety and bioavailability profiles of the long-acting products are the same or improved over the parent product. A review of the long-acting drugs provides compelling evidence to recommend that generic drug-controlled release products may be eligible for alternative regulatory programs.

Pharmacokinetics and analgesic effects of intravenous, intramuscular or subcutaneous buprenorphine in dogs undergoing ovariohysterectomy: a randomized, prospective, masked, clinical trial

BACKGROUND

Buprenorphine is used for canine postoperative pain management. This study aimed to describe the pharmacokinetics and evaluate the analgesic efficacy of buprenorphine (Simbadol, 1.8 mg/mL) administered by different routes in dogs undergoing ovariohysterectomy. Twenty-four dogs were included in a randomized, prospective, masked, clinical trial. Buprenorphine (0.02 mg/kg) was administered intravenously (IV), intramuscularly (IM) or subcutaneously (SC) (n = 8/group) 0.5 h before general anesthesia with propofol-isoflurane. Carprofen (4.4 mg/kg SC) was administered after anesthetic induction and before ovariohysterectomy. Pain was scored using the short-form Glasgow composite pain scale for dogs (SF-GCPS). Dogs were administered morphine (0.25 mg/kg IV) when SF-GCPS scores were ≥ 5/20. Blood sampling was performed up to 720 min after drug administration. Plasma buprenorphine and norbuprenorphine concentrations were analyzed using liquid chromatography mass spectrometry. Pharmacokinetics of buprenorphine was described using a non-compartmental model (PK Solver 2.0). Statistical analysis was performed using linear mixed models and Fisher's exact test (p < 0.05).

RESULTS

Pain scores were significantly higher than baseline after IV (0.5-2 h), IM (0.5-3 h) and SC (0.5-4 h) but not among groups. Prevalence of rescue analgesia was significantly higher in SC (7/8 dogs) than IV (2/8) but not different between IV and IM (3/8) or IM and SC. The frequency of rescue analgesia was not significantly different among groups (IV = 2, IM = 5 and SC = 9). Norbuprenorphine was not detected. For IV, IM and SC administration, clearance was 1.29, 1.65 and 1.40 L/hour/kg, volume of distribution was 6.8, 14.2 and 40.1 L/kg, the elimination half-life was 3.7, 5.7, 22 h, and the area under the plasma concentration-time curved extrapolated to infinity was 15.7, 12.4 and 16.4 ng/mL/hour, respectively. Bioavailability for IM and SC was 62.6 and 40%, respectively. Maximum plasma concentrations of buprenorphine were 6.2 and 1.3 ng/mL at 0.14 and 0.33 h after IM and SC administration, respectively.

CONCLUSIONS

The route of administration influences the analgesic efficacy of buprenorphine in dogs. SC administration of buprenorphine failed to provide clinical analgesia due to erratic drug absorption. At the doses administered, the IV and IM routes are preferred for postoperative analgesia.

Analgesia during Monkeypox Virus Experimental Challenge Studies in Prairie Dogs (Cynomys ludovicianus)

Because human patients with monkeypox virus (MPXV) infection report painful symptoms, it is reasonable to assume that animals infected with MPXV experience some degree of pain. Understanding whether and how analgesics affect MPXV disease progression is crucial when planning in vivo challenge experiments. In the current study, we challenged prairie dogs with a low dose (4 ×10³ pfu) of MPXV and treated with meloxicam (NSAID) or buprenorphine (opioid); control animals did not receive analgesia or received analgesia without MPXV challenge. Subsets of animals from each group were serially euthanized during the course of the study. Disease progression and viral kinetics were similar between groups, but MXPVinfected, meloxicam-treated animals showed increasing trends of morbidity and mortality compared with other groups. Differences between no-analgesia MPXV-infected control animals and MPXV-infected animals treated with buprenorphine were minimal. The findings in the current study allow more informed decisions concerning the use of analgesics during experimental MPXV challenge studies, thereby improving animal welfare. In light of these findings, we have modified our pain scale for this animal model to include the use of buprenorphine for pain relief when warranted after MPXV challenge.

Evaluation of Analgesic Patches in Cynomolgus Macaques (Macaca fascicularis)

Opioids are widely used in veterinary and human medicine to manage pain. However, there is a paucity of information in the literature regarding the pharmacokinetics of opioid transdermal patches (TDP) in NHP. Therefore, to determine whether opioid TDP attain therapeutic concentrations in NHP, the pharmacokinetics of fentanyl (25 μg/h) and buprenorphine (10 and 20 μg/h) TDP were evaluated in naïve, adult, male cynomolgus macaques (n = 4) in a crossover study. Plasma opioid levels were determined by tandem liquid chromatography-mass spectrometry. The AUC_0-inf for fentanyl and the low and high dose buprenorphine patches were 115 ± 14, 462 ± 74, and 778 ± 344 ng× h/mL, and the plasma half-lifes were 22 ± 4, 77 ± 27, and 42 ± 11 h, respectively. No adverse effects were noted throughout the study. Minimal therapeutic concentrations for fentanyl (0.2 ng/mL) and buprenorphine (0.1 ng/mL) were achieved in all macaques within 8 h of fentanyl and 24 h of buprenorphine TDP application. Therapeutic levels for the fentanyl and low- and high-dose buprenorphine patches were maintained for 96, 120, and 144 h, respectively. These findings suggest that 25-μg/h fentanyl patches should be replaced every 4 d, and the low- and high-dose buprenorphine patches should be replaced every 5 and 6 d, respectively. The results of this study show that fentanyl and buprenorphine patches achieve minimal therapeutic levels for clinically relevant periods of time and should be considered viable options for pain management in cynomolgus macaques.

Mechanical sensory threshold in Cavalier King Charles spaniels with syringomyelia-associated scratching and control dogs

It is assumed that Cavalier King Charles spaniels with Chiari-like malformation and syringomyelia experience central neuropathic pain. An association between spinal cord parenchymal lesions and specific clinical signs (e.g. spontaneous and evoked scratching, withdrawal, and paroxysmal pain manifestations with vocalisation) has been suggested. This led to the hypothesis that mechanical sensory threshold is altered in clinical cases. The aim of this study was to quantify the cervical mechanical sensory threshold using Semmes-Weinstein monofilaments in nine Cavalier King Charles spaniels with Chiari-like malformation and assumed syringomyelia-associated central neuropathic pain compared to eight control dogs. Clinical and neurological examination including magnetic resonance imaging was undertaken. Mean mechanical sensory threshold was not significantly different between case and control dogs (t-test on log10 transformed data; P=0.25). Substantial variation within and between dogs was seen, with individual thresholds ranging from 0.04 to 26g in case dogs and from 0.02 to 10g in control dogs. Based on these results, it is unlikely that Cavalier King Charles spaniels with Chiari-like malformation and syringomyelia have increased mechanical sensation characterised by lower mechanical sensory threshold when quantified with Semmes-Weinstein monofilaments. Whether clinical cases experience central neuropathic pain remains unknown. The assessment of sensory function in dogs with assumed central neuropathic pain should be multimodal and include not only mechanical but also tactile and thermal threshold quantification. The use of threshold quantification in a clinical setting is challenging due to an insufficient signal relative to the biological background noise within and between dogs.

The pharmacokinetics and analgesic effects of extended-release buprenorphine administered subcutaneously in healthy dogs

Buprenorphine is a partial μ agonist opioid used for analgesia in dogs. An extended-release formulation (ER-buprenorphine) has been shown to provide effective analgesia for 72 hr in rats and mice. Six healthy mongrel dogs were enrolled in a randomized, blinded crossover design to describe and compare the pharmacokinetics and pharmacodynamics of ER-buprenorphine administered subcutaneous at 0.2 mg/kg (ER-B) and commercially available buprenorphine for injection intravenously at 0.02 mg/kg (IV-B). After drug administration, serial blood samples were collected to measure plasma buprenorphine concentrations using liquid chromatography/mass spectrometry detection. Heart rate, respiratory rate, body temperature, sedation score, and thermal threshold latency were recorded throughout the study. Median (range) terminal half-life, time to maximum concentration, and maximum plasma concentration of ER-buprenorphine were 12.74 hr (10.43-18.84 hr), 8 hr (4-36 hr), and 5.00 ng/ml (4.29-10.98 ng/ml), respectively. Mild bradycardia, hypothermia, and inappetence were noted in both groups. Thermal threshold latency was significantly prolonged compared to baseline up to 12 hr and up to 72 hr in IV-B and ER-B, respectively. These results showed that ER-buprenorphine administered at a dose of 0.2 mg/kg resulted in prolonged and sustained plasma concentrations and antinociceptive effects up to 72 hr after drug administration.

Subcutaneous Implants of a Cholesterol-Triglyceride-Buprenorphine Suspension in Rats

A Target Animal Safety protocol was used to examine adverse events in male and female Fischer F344/NTac rats treated with increasing doses of a subcutaneous implant of a lipid suspension of buprenorphine. A single injection of 0.65 mg/kg afforded clinically significant blood levels of drug for 3 days. Chemistry, hematology, coagulation, and urinalysis values with 2- to 10-fold excess doses of the drug-lipid suspension were within normal limits. Histopathology findings were unremarkable. The skin and underlying tissue surrounding the drug injection were unremarkable. Approximately 25% of a cohort of rats given the excess doses of 1.3, 3.9, and 6.5 mg/kg displayed nausea-related behavior consisting of intermittent and limited excess grooming and self-gnawing. These results confirm the safety of cholesterol-triglyceride carrier systems for subcutaneous drug delivery of buprenorphine in laboratory animals and further demonstrate the utility of lipid-based carriers as scaffolds for subcutaneous, long-acting drug therapy.

Companion Animal Owner Perceptions, Knowledge, and Beliefs Regarding Pain Management in End-of-Life Care

The senior companion animal is the fastest growing segment of the pet population. End-of-life care, quality of life, and pain management (PM) are extremely important to pet owners. Research into PM and end-of-life care is essential due to lack of information on owner knowledge, attitudes, and beliefs. A survey was developed to gather information from owners. Surveys were developed using expert focus groups, and participants were recruited through social media. Survey validation employed emergent themes and grounded theory. Data from respondents (n = 986) were analyzed using descriptive statistics, Kruskal-Wallis, Jonckheere-Terpstra, or Wilcoxon rank-sum tests, with post hoc adjustment. Approximately 87% of respondents felt that euthanizing for unmitigated pain was appropriate. Households where there were multiple pets, both cats and dogs, and owners who were not first-time pet owners showed even greater preferences (P < .05) for euthanasia with unmitigated pain. Pain control was important to respondents, but owners lacked knowledge and had unrealistic attitudes and beliefs about treatment options, costs, and long-term feasibility. Limitations of this research included homogeneity of online survey respondents and convenience sampling. Translational research should be fostered to increase the availability and affordability of PM techniques in veterinary practice.

Subcutaneous Implants of Buprenorphine-Cholesterol-Triglyceride Powder in Mice

Subcutaneous drug implants are convenient systems for the long-term delivery of drugs in animals. Lipid carriers are logical tools because they generally allow for higher doses and low toxicity. The present study used an US Food and Drug Administration Target Animal Safety test system to evaluate the safety of a subcutaneous implant of a cholesterol-triglyceride-buprenorphine powder in 120 BALB/c mice. Mice were evaluated in 4- and 12-day trials with 1- and 5-fold doses of the intended 3 mg/kg dose of drug. One male mouse treated with three 3 mg/kg doses and surgery on days 0, 4, and 8 died on day 9. The cause of death was not determined. In the surviving 119 mice there was no evidence of skin reaction at the site of the implant. Compared to control animals treated with saline, weight measurements, clinical pathology, histopathology, and clinical observations were unremarkable. These results demonstrate that the lipid carrier is substantially safe. Cholesterol-triglyceride-drug powders may provide a valuable research tool for studies of analgesic and inflammatory drug implants in veterinary medicine.

Safety studies of post-surgical buprenorphine therapy for mice

The use of appropriate analgesia in laboratory mice may be suboptimal because of concerns about adverse events (AE). Target Animal Safety trials were conducted to determine the safety of an extended-release suspension of buprenorphine. Drug or control suspensions were injected subcutaneously in surgically-treated BALB/c mice anesthetized with ketamine-xylazine to mimic post-operative conditions in which the compound might commonly be administered. Single and repeat five-fold (5×) excesses of the 3.25 mg/kg intended dose were used to provoke potential AE. Trials included prospective measurements of weight changes, blood chemistry, hematology, and histopathology. Clinical and histopathology findings were similar in drug-treated and control mice in a four-day trial using a single 16.25 mg/kg, 5× overdose of the drug. In a 12-day trial, which used a total buprenorphine dose of 48.75 mg/kg, clinical and histopathology values were also similar in control and drug-treated female mice. In the male arm of the repeat-overdose trial, two of eight mice died on the morning of day 12, three days following the third 16.25 mg/kg overdose administration. Histopathology did not reveal a cause of death. In a 14-month trial using a single 3.25 mg/kg dose of the drug, no significant findings identified potential AE. These findings indicate a high tolerance to an extended-release buprenorphine suspension administered post-operatively in mice with appropriate husbandry.

Handheld mechanical nociceptive threshold testing in dairy cows - intra-individual variation, inter-observer agreement and variation over time

Objective

To examine the use of handheld methodology to assess mechanical nociceptive threshold (MNT) on cows kept loose-housed.

Study design

Prospective randomized partial cross-over experimental study. A one-factor (test day) design was used to evaluate MNT over time.

Animals

One hundred and fifteen healthy, loose-housed Danish Holstein cattle.

Methods

We evaluated intra-individual variation, inter-observer agreement and variation over time of MNT using two handheld devices and two stimulation sites. Mechanical, ramped stimulations were performed with an algometer (6.5 mm diameter steel probe, 0–10.0 kgf) or an electronic von Frey device (plastic tip with diameter 0.8 mm, 0–1000 gf). Each cow received 5–6 consecutive stimulations within a 2 × 5 cm skin area on the dorsal or lateral aspect of the left third metatarsus until an avoidance reaction occurred. We investigated the difference in precision [expressed as coefficient of variation (CV)] between the combinations of devices and stimulation sites. The inter-observer agreement and the difference in MNT between test day 1, 3, 7, 10 and 24 were investigated for selected combinations. Data were analysed in mixed models and Bland-Altman as relevant.

Results

The CVs did not differ [range 0.34–0.52 (p = 0.1)]. Difference between observers (95% limits) was 0.2 kgf (2.8) and 4 gf (369) for the algometer and von Frey device, respectively. Mechanical nociceptive threshold increased from 361 on test day one to 495 gf on test day 24 (p < 0.01).

Conclusion and clinical relevance

All methods showed a high degree of intra-individual variation, and no combination of device and stimulation site showed superior precision. Mean difference between observers was low, and MNT was not consistent over time. Further development of the methods is required before they can be used in research to investigate possible relations between claw lesions and hyperalgesia.