Melbourne Veterinary School - Research Publications
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ItemMathematical modeling and simulation in animal health. Part III: Using nonlinear mixed-effects to characterize and quantify variability in drug pharmacokinetics(WILEY, 2018-04-01)A common feature of human and veterinary pharmacokinetics is the importance of identifying and quantifying the key determinants of between-patient variability in drug disposition and effects. Some of these attributes are already well known to the field of human pharmacology such as bodyweight, age, or sex, while others are more specific to veterinary medicine, such as species, breed, and social behavior. Identification of these attributes has the potential to allow a better and more tailored use of therapeutic drugs both in companion and food-producing animals. Nonlinear mixed effects (NLME) have been purposely designed to characterize the sources of variability in drug disposition and response. The NLME approach can be used to explore the impact of population-associated variables on the relationship between drug administration, systemic exposure, and the levels of drug residues in tissues. The latter, while different from the method used by the US Food and Drug Administration for setting official withdrawal times (WT) can also be beneficial for estimating WT of approved animal drug products when used in an extralabel manner. Finally, NLME can also prove useful to optimize dosing schedules, or to analyze sparse data collected in situations where intensive blood collection is technically challenging, as in small animal species presenting limited blood volume such as poultry and fish.
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ItemInternal aorto-iliac thrombosis in a Thoroughbred: Unsuccessful surgical thrombectomy, a proposed aetiopathogenesis and spontaneous partial regression(WILEY, 2019-07-01)Summary A 4‐year‐old Thoroughbred gelding with severe left hindlimb lameness and colic‐like signs lasting 30–60 min post‐exercise was diagnosed with unilateral internal aorto‐iliac thrombosis. The thrombus was identified using transrectal ultrasonography in the terminal aorta and was initially thought to extend into the left external iliac artery. However, attempted thrombectomy via a left femoral arteriotomy performed under general anaesthesia using thrombectomy and angioplasty catheters was unsuccessful, as the thrombus was located in the left internal iliac artery. Transrectal ultrasound evaluation was repeated monthly for 12 months post‐operatively during which time the gelding remained asymptomatic at rest. As removal of thrombi in the external but not internal iliac artery may be possible, correct diagnosis of the location of the thrombus is critical in preventing unnecessary attempts at surgical correction. The aetiology remains unknown, but altered haemodynamics within the abdominal aorta with mechanical stresses during intense exercise are proposed as a cause of thrombus formation. The sequential monitoring of this case also conflicts the assumption that thrombi in this location propagate over time as partial regression was observed 6 months after referral and 9 months after onset of clinical signs.
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ItemEffect of distal ulnar ostectomy on carpal joint stability during weight bearing in the dog(WILEY, 2017-11-01)OBJECTIVE: To assess the influence of a 50% distal ulnectomy on mediolateral carpal stability in the dog. STUDY DESIGN: Canine cadaveric study. SAMPLE POPULATION: Seven canine thoracic limbs METHODS: Thoracic limbs were placed in a jig to mimic weight bearing with a load representing 30% of body weight. Carpal extension angle was standardized at 190° ± 5°. Frontal plane carpal angles were measured with the limb loaded on craniocaudal radiographs before and after ulnectomy. Valgus and varus stress radiographs with the limb loaded were acquired before and after ulnectomy. The limbs were palpated and were subjectively graded for valgus or varus instability by 2 investigators before and after ulnectomy. RESULTS: Mean (±SD) valgus angulation increased after ulnectomy (2.1° ± 1.7°; P = .017; CI95 = 0.5°-3.7°) when the limb was loaded without valgus or varus stress applied. Mean valgus angulation increased after ulnectomy (2.7° ± 2.8°; P = .032; CI95 = -0.2°-5.5°) when valgus stress was applied to the loaded limb. Varus angulation was unchanged after ulnectomy (0.6° ± 4.6°; P = .383; CI95 = -4.2°-5.3°) when varus stress was applied to the loaded limb. Palpation detected increased valgus score after ulnectomy. CONCLUSION: Distal ulnectomy with excision of the lateral styloid process induces a slight increase in valgus in canine cadaver carpi. The clinical consequences of that valgus on carpal function and health should be assessed in clinical patients.
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ItemDetermination of testosterone esters in the hair of male greyhound dogs using liquid chromatography-high resolution mass spectrometry(WILEY, 2018-03-01)The doping of greyhound dogs with testosterone is done in an attempt to improve their athletic performance, but such doping cannot easily be confirmed, especially in male dogs owing to the natural presence of endogenous testosterone. As testosterone is usually administered as its esters, their direct detection in hair would provide confirmatory evidence of the administration of a pharmaceutical product. This article demonstrates that the use of a liquid chromatography-high resolution mass spectrometry method with heated electrospray ionisation (HESI) combined with the use of amino solid-phase extraction (SPE) cartridges for sample clean-up, is suitable for the sensitive determination of propionate, phenyl propionate, isocaproate, decanoate, and enanthate esters of testosterone in greyhound hair. The method is linear over the range, 0.1 μg/kg-10 μg/kg, for all the testosterone esters analysed. The limits of detection (LOD) are 0.05 μg/kg for testosterone phenyl propionate, isocaproate, and decanoate, 0.025 μg/kg for testosterone propionate, and 0.25 μg/kg for testosterone enanthate. This method was applied to hair samples collected from male greyhounds before and after a single administration of a product containing several testosterone esters, each of which could be detected up to 100 days post-administration. The study also demonstrates that tail hair is the specimen of choice for the analysis of testosterone in dog hair and that washing of dogs does not impact the analysis of testosterone esters in hair. This method may be useful in racing regulation for the detection of illegitimate use of testosterone in all species.
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ItemPrior joint disease is associated with increased risk of periarticular histiocytic sarcoma in dogs(WILEY, 2018-03-01)Periarticular histiocytic sarcoma (PAHS) is the most common synovial tumour in dogs and is characterized by aggressive local disease with a high rate of distant metastasis. Previously, an association between PAHS and prior joint disease has been demonstrated in the Bernese Mountain Dog breed and suggested in the Rottweiler. We hypothesized that this association would be present in other breeds and investigated this via a retrospective, case-controlled analysis. Cases were dogs diagnosed with PAHS of the stifle or elbow. Controls were age, breed and sex-matched dogs without a diagnosis of histiocytic sarcoma. Diagnosis of prior joint disease was determined based on review of medical records and direct veterinarian and owner communications. Data were evaluated using logistic regression, 2-sampled t tests, and chi-squared analysis. Our study population consisted of 28 cases and 46 controls, including Flat-Coated, Golden and Labrador Retrievers, Rottweilers, English Bulldogs, Shih Tzus, Australian Shepherds, Staffordshire Terriers and mixed breed dogs. Dogs with PAHS were more likely to have prior joint disease in the tumour-affected joint compared with the control population (odds ratio [OR] = 13.42, P < .0001, 95% confidence interval [CI] = 4.33-48.63). A total of 88.2% of dogs with stifle PAHS had prior joint disease in their tumour-affected joint, most commonly cranial cruciate ligament rupture. This study confirms that the previously noted association between prior joint disease and PAHS in Bernese Mountain Dogs also applies to other breeds. Additional studies are needed to further investigate for a causal relationship.
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ItemRetrospective evaluation of cats with elapid snake envenomation associated neurotoxicity requiring mechanical ventilation: 12 cases (2005-2014)(WILEY, 2017-09)OBJECTIVE: To retrospectively determine the population and outcome characteristics of a cohort of Australian elapid snake envenomed cats requiring mechanical ventilation (MV). DESIGN: Retrospective observational study (2005-2014). SETTING: Academic veterinary emergency and critical care service. ANIMALS: Twelve cats undergoing MV for elapid snake envenomation. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The medical records were searched to identify cats requiring MV as part of treatment for elapid snake envenomation. Signalment, the indication for, duration of and complications associated with MV, duration of hospitalization, and survival to hospital discharge were recorded for each of the enrolled cases. Seven cats (58.3%) underwent MV because of presumed unsustainable respiratory effort and 5 cats (41.7%) for respiratory arrest. Eleven cats (91.7%) were successfully weaned from MV and survived to hospital discharge. No cats developed ventilator associated pneumonia or pneumothorax. The median duration of MV was 19.5 hours for the survivors (range 7.0-37.0 hours) and median duration of hospitalization was 3.5 days (range 2.4-14.9 days). CONCLUSIONS: Cats requiring MV for elapid snake envenomation have a favorable outcome and require a relatively short period of MV. Complications encountered are unlikely to influence outcome.
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ItemClinicopathologic features of lingual canine T-zone lymphoma(WILEY, 2018-03-01)Canine T-zone lymphoma (TZL) is a subtype of T-cell lymphoma characterized by unique histologic pattern and cytomorphology, immunophenotypic loss of CD45 expression, and an indolent clinical behaviour. Dogs with TZL typically present with 1 or more enlarged lymph nodes and/or lymphocytosis. We describe a novel extranodal presentation of TZL involving the tongue. Twelve dogs with tongue masses were diagnosed with lingual TZL based on a variable combination of immunophenotyping via flow cytometry, cytology, histopathology, immunohistochemistry and/or PCR for antigen receptor rearrangement (PARR) assay. Eleven dogs exhibited concurrent lymphocytosis and/or lymph node enlargement. Three cases were initially diagnosed as plasma cell tumours based on histology alone, thereby revealing a potential diagnostic challenge. Seven dogs achieved clinical remission and 4 achieved stable disease following variable treatment, consistent with the indolent nature of typical TZL involving the lymph nodes and peripheral blood. In 1 case the TZL resulted in progressive disease and failure to respond to treatment. In this case, the TZL exhibited histologic features of a higher grade neoplasm. This case series highlights a unique presentation of TZL and identifies a new differential diagnosis for lingual neoplasia. In this study, we characterize the clinical presentation, diagnostic features and patient outcomes of 12 dogs with lingual TZL.
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ItemChemical stability of morphine and methadone, and of methadone in combination with acepromazine, medetomidine or xylazine, during prolonged storage in syringes(WILEY, 2017-08-01)OBJECTIVE: To assess the chemical and physical stability of morphine and methadone stored in syringes for 12 months and of methadone when mixed with acepromazine, medetomidine or xylazine. METHODS: A high-performance liquid chromatography (HPLC) technique was developed and validated for the analysis of morphine and methadone. Morphine and methadone were dispensed into syringes and stored at 25°C/60% relative humidity (RH) and 40°C/75% RH. Solutions containing mixtures of methadone combined with acepromazine, medetomidine or xylazine were stored in syringes at 25°C/60%RH. At initiation, after 1 week and then 1, 3, 6, 9 and 12 months, samples were analysed by HPLC for the quantification of the morphine or methadone. Measured concentrations were assessed as a function of storage time and temperature using linear regression statistics to calculate stability. RESULTS: When stored at 40°C/75%RH as pre-dispensed syringes, severe physical and chemical changes were observed after the third month for both morphine and methadone. In contrast, at 25°C/60%RH both drugs remained chemically stable for 12 months, with concentration variations not exceeding a 5% change from initiation as stipulated in VICH stability guidelines. When in combination with acepromazine or xylazine, methadone also remained chemically stable, but the combination with medetomidine failed stability criteria prior to 6 months. Precipitation compromised the physical stability of methadone in all unsealed syringes prior to 9 months' storage. CONCLUSION: Pre-dispensing morphine or methadone into unsealed syringes compromises the drugs' physical stability. Mixing of methadone with other drugs can degrade its chemical stability.
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ItemHistiocytic sarcoma in 14 miniature schnauzers - a new breed predisposition?(WILEY, 2017-08-01)OBJECTIVES: To describe a series of miniature schnauzers diagnosed with histiocytic sarcoma and assess for possible breed predisposition. MATERIALS AND METHODS: Medical records of miniature schnauzers with a diagnosis of histiocytic sarcoma between January 2008 and April 2015 were reviewed. Data collected included signalment, body weight, presenting complaint, date of diagnosis, clinicopathologic and diagnostic imaging findings, treatment, therapeutic response, date of death or last follow-up and necropsy findings. Breed predisposition was assessed with odds ratios, using breed-matched dogs without histiocytic sarcoma admitted during the study period as controls. Pedigree analysis was performed for dogs with available registration information. RESULTS: Fourteen miniature schnauzers were diagnosed with histiocytic sarcoma during the study period, making them over-represented among the hospital population (odds ratio=4·8, P=0·0009). Disease was considered localised in ten dogs and disseminated in four. Of the dogs with localised disease, nine were diagnosed with primary pulmonary histiocytic sarcoma based on the presence of a large pulmonary mass with (n=7) or without (n=2) evidence of intra-thoracic metastasis, and one had gastric histiocytic sarcoma with nodal metastasis. Treatments varied, but an aggressive clinical course was found in most patients. Pedigree analysis revealed a recent common ancestor for a subset of the dogs assessed. CLINICAL SIGNIFICANCE: Miniature schnauzers were over-represented among dogs with histiocytic sarcoma in this patient population. Pedigree analysis supports an inherited risk factor, which has not previously been suggested in the breed. Primary pulmonary involvement with or without intra-thoracic metastasis was common in this cohort.
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ItemImpact of diet on faecal output and caecotroph consumption in rabbits(WILEY, 2017-01-01)OBJECTIVES: To assess the impact of four rabbit diets (hay only, extruded diet with hay, muesli with hay and muesli only) on faecal pellet size, faecal output and caecotrophy. MATERIALS AND METHODS: Thirty-two Dutch rabbits were studied over 17 months. Faecal pellet size and weight were measured in weeks 3, 9, 21 and 43 and faecal output in weeks 10, 22 and 45. Number of uneaten caecotrophs was recorded weekly. RESULTS: Faecal pellets were consistently smaller and lighter in rabbits fed muesli only, and the size of pellets produced by those fed muesli with hay decreased over the course of the study. Faecal output was greatest in rabbits with the highest hay intake. Uneaten caecotrophs were found in greatest frequency in rabbits fed muesli. CLINICAL SIGNIFICANCE: Muesli diets have a negative effect on faecal output and caecotroph ingestion and may therefore predispose to digestive disorders. Higher hay intake is associated with greater faecal output and fewer uneaten caecotrophs and may assist in preventing the gastrointestinal stasis.