Pharmacokinetic profile of amoxicillin and its glucuronide-like metabolite when administered subcutaneously to koalas (Phascolarctos cinereus)

Amoxicillin was administered as a single subcutaneous injection at 12.5 mg/kg to four koalas and changes in amoxicillin plasma concentrations over 24 hr were quantified. Amoxicillin had a relatively low average ± SD maximum plasma concentration (C_max) of 1.72 ± 0.47 µg/ml; at an average ± SD time to reach C_max (T_max) of 2.25 ± 1.26 hr, and an elimination half-life of 4.38 ± 2.40 hr. The pharmacokinetic profile indicated relatively poor subcutaneous absorption. A metabolite was also identified, likely associated with glucuronic acid conjugation. Bacterial growth inhibition assays demonstrated that all plasma samples other than t = 0 hr, inhibited the growth of Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 29213 to some extent. Calculated pharmacokinetic indices were used to predict whether this dose could attain a plasma concentration to inhibit some susceptible Gram-negative and Gram-positive pathogens. It was predicted that a twice daily dose of 12.5 mg/kg would be efficacious to inhibit susceptible bacteria with an amoxicillin minimum inhibitory concentration (MIC) ≤ 0.75 µg/ml such as susceptible Bordetella bronchiseptica, E. coli, Staphylococcus spp. and Streptococcus spp. pathogens.     

Symmetric dimethylarginine values in koalas (Phascolarctos cinereus) based on oxalate nephrosis status

Oxalate nephrosis is a prevalent renal disease in koalas (Phascolarctos cinereus) of the Mount Lofty Ranges population in South Australia. The symmetric dimethylarginine (SDMA) assay is widely used in companion animals to diagnose renal disease, particularly in the early stages. This study aimed to determine: (1) reference intervals for SDMA in koalas and (2) SDMA values of koalas with oxalate nephrosis. Blood samples were collected from 41 Mount Lofty Ranges koalas euthanased on welfare grounds. Koalas were necropsied and, based on renal histopathology, were classified as unaffected (n = 22) or affected (n = 19) by oxalate nephrosis. Serum or plasma samples were analysed for creatinine, urea and SDMA and urine samples for urine specific gravity (USG). The reference interval for SDMA in unaffected koalas was 2.4–22.9 μg/dL. In koalas with oxalate nephrosis, SDMA was elevated in 74% of cases above the upper limit of the confidence interval. SDMA was elevated in three affected koalas with normal creatinine values. A positive correlation was found between SDMA and creatinine (R = 0.775, P < 0.001) and SDMA and urea (R = 0.580, P < 0.001) and a negative correlation between SDMA and USG (R = −0.495, P = 0.027). In conclusion, SDMA correlates well with other commonly used tests of renal function in koalas and should be included as part of the standard diagnostic process to increase the accuracy of oxalate nephrosis diagnosis in koalas.     

Malocclusions in the koala (Phascolarctos cinereus)

Malocclusions are a misalignment or incorrect positioning of the teeth when the upper and lower jaws close. These are poorly described in the koala and can result in irregular mastication which can have lifelong effects on body condition and oral health. A total of 370 koalas from two populations in Queensland (295) and one in South Australia (75) were examined for malocclusions. The prevalence of malocclusions in South Australian free‐ranging koalas, captive Queensland koalas and Queensland free‐ranging koalas was 39% (44), 30% (29) and 22% (29) respectively. Four types of malocclusion were identified based on severity of misalignment of the incisor/canine region, types 1, 2, 3 and 4. Maxillary overbite measurements of the molariform teeth were determined and these anisognathic values were then used to describe malocclusions within familial relationships in captive colonies. Captive koalas with a malocclusion had narrower mandibular width that ranged between 0.5 and 1% less than the normal measurements. The specific malocclusions reported in this study affected individuals by leading to tooth rotation, mobility and erosion with inefficient mastication of food and vegetation compaction. These changes increased the oral cavity pathology, by placing animals at risk of periodontal disease. There was evidence of familial links to malocclusion types in captive animals. Therefore captive breeding recommendations should consider known koala malocclusion traits to minimise their effect on future generations.     

Review of some pharmacokinetic and pharmacodynamic properties of anti‐infective medicines administered to the koala (Phascolarctos cinereus)

Although koalas are iconic Australian animals, no pharmacokinetic studies of any first‐line medicines used to treat diseased or injured koalas had been published prior to 2010. Traditionally, medicine dosages suggested for this species underwent linear extrapolation from those recommended for domesticated species. The koala, a specialist folivore whose natural diet consists of almost exclusively Eucalyptus spp. foliage has anatomical and physiological adaptations for detoxifying their diet which also affect medicine pharmacokinetic profiles. This review addresses aspects of medicine absorption, clearance, and other indices (such as medicine binding to plasma proteins) of enrofloxacin/marbofloxacin and chloramphenicol used for the systemic treatment of chlamydiosis, and fluconazole ± amphotericin, and posaconazole for the treatment of cryptococcosis. Based on observations from published studies, this review includes suggestions to improve therapeutic outcomes when administering medicines to diseased koalas.     

Antibiotics for the preservation of koala (Phascolarctos cinereus) semen

Aim To determine the normal microbial flora of the koala ejaculate and prepuce in order to select appropriate antibiotics for addition into diluents designed for the preservation of semen.
Procedure Bacteriological samples of the koala prepuce (n = 12) and ejaculate (n = 20) were submitted for microbial culture and sensitivity testing. Microbial flora of ejaculates collected by electroejaculation and artificial vagina were compared. The effects of varying concentrations of penicillin G and gentamicin on sperm motility and on the growth of bacteria in diluted semen stored at room temperature and 16°C over a 24 h period were investigated.
Results A range of bacteria was isolated from the koala prepuce and ejaculate. The predominant organisms in semen collected by electroejaculation and artificial vagina were Corynebacterium spp, none of which could be assigned to any recognised species. The addition of penicillin G and gentamicin to a PBS-based diluent at dose rates of 1000 to 2000 IU/mL and 100 to 200 m g/mL respectively, resulted in no adverse effect on sperm motility over a 24 h incubation period. Penicillin G (1000 IU/mL) and gentamicin (100 m g/mL) prevented growth of bacterial contaminants in diluted koala semen.
Conclusion By controlling the growth of bacteria in extended koala semen, penicillin G and gentamicin are likely to lengthen the period by which spermatozoa can be stored at 16°C and reduce the possibility of disease transmission during artificial insemination procedures.     

INTRAVENOUS UROGRAPHY IN THE KOALA (Phascolarctos cinereus)

Urograms were performed on 16 adult koalas to evaluate this procedure for use in the koala. Because there is only small amount of intraabdominal fat, radiographs of the abdomen of koalas lack detail. Contrast medium was excreted more slowly in the koala than in the dog and there was considerable variation in the rate of excretion between koalas. The results of this study indicated that urography was valuable technique for assessing renal anatomy, but there was considerable variation in the time for excretion of the contrast medium.     

Diabetes mellitus in a koala (Phascolarctos cinereus)

Objective To describe a case of diabetes mellitus in a koala (Phascolarctos cinereus).
Design A case report with controls.
Procedures We describe clinical and laboratory findings in a 6-year-old, free-living, female koala presented with traumatic injury and subsequently found to have polydipsia, hyperglycaemia and glucosuria. Over a 5 week period, serum biochemical analyses, haematological examinations, urinal-yses, measurement of serum insulin and fructosamine concentrations, necropsy, histopathological examination of a range of tissues and immunohistochemical examination of the pancreas for insulin-containing cells were done. For reference purposes, serum insulin and fructosamine concentrations were determined in four and two healthy koalas, respectively, and three healthy koalas pancreases were examined histo-logically and immunohistochemically.
Results The koala had persistent hyperglycaemia, hyperlipidaemia, hyponatraemia, hypochloraemia and glucosuria. Serum insulin concentration of the diabetic koala was only marginally smaller than that of healthy koalas, but all concentrations were smaller than reference concentrations in dogs and people. Fructosamine concentration did not allow the diabetic koala to be distinguished from healthy koalas and concentrations of all koala analytes were greater than expected for healthy dogs and people. Histopathological examination revealed extensive degeneration of pancreatic islet cells and fatty infiltration of hepatocytes. Immunoperoxidase staining revealed decreased or absent insulin in the b cells of the affected koala.
Conclusion Clinical signs, clinicopathological results and histopathological changes were consistent with diabetes mellitus. The pathogenesis of the condition could not be determined but may have been related to the administration of a parenteral corticosteroid preparation, the stress of capture or tissue damage and inflammation.     

Oxalate poisoning in a koala (Phascolarctos cinereus)

SUMMARY A case of suspected acute oxalate poisoning is reported in an aged male koala. The animal had extensive renal oxalosis and a haemorrhagic bladder wall when autopsied. The source of the oxalate was not detected.     

Disseminated coccidoidomycosis in a koala (Phascolarctos cinereus)

A16-yr-old male koala (Phascolarctos cinereus) presented for nonspecific signs of illness and weight loss. Despite 2 mo of diagnostics and supportive care, the koala's health declined and euthanasia was elected. On histopathologic examination, lesions containing fungal organisms morphologically consistent with coccidioidomycosis were found in the lung, liver, spleen, kidney, lymph node, heart, eye, and bone marrow. Although disseminated infection was present, the koala was IgM and IgG seronegative for Coccidioides spp. 1 mo prior to euthanasia.     

Thymic lymphosarcoma of T cell lineage in a koala (Phascolarctos cinereus)

Objective To diagnose and characterise thymic lymphosarcoma in a koala.
Design A pathological case.  

Animal

Seven-year-old female koala.
Procedure The neoplastic process was investigated macroscopically, haematologically, histologically and immunohistologically.
Results The koala had difficulty swallowing because of a medial swelling in the lower neck. Biopsy of this mass and blood examination revealed lymphosarcoma with a leukaemic manifestation; necropsy and histopathological examination showed the mass to be thymus. Palatine tonsils, cervical, axillary and mesenteric lymph nodes, spleen, liver, gut, bronchi, genitalia and bone marrow were infiltrated by neoplastic cells. Immunohistological staining of the thymic mass, cervical and mesenteric lymph nodes, bone marrow, spleen and gut revealed the neoplastic cells to be of T lymphocyte origin (positive for both anti-human CD3 and CD5).  

Conclusions

It is speculated that the neoplastic process originated in the thymus and was disseminated by bloodborne neoplastic cells: This first report of thymic lymphosarcoma in a marsupial confirms that antibodies raised originally to investigate human lymphoid neoplasia can cross-react with neoplastic lymphocytes in koalas.     

Histological survey for oxalate nephrosis in Victorian koalas (Phascolarctos cinereus)

The Mount Lofty Ranges koala (Phascolarctos cinereus) population in South Australia has a high prevalence of the renal disease oxalate nephrosis, for which an underlying genetic cause is suspected. South Australian koalas primarily originate from those in French Island, Victoria; however, oxalate nephrosis has not previously been reported in Victorian koalas. Examination of kidney tissue sections from 63 koalas across Victoria found that nine koalas were affected by oxalate nephrosis (14.3%). These included 2/5 koalas from French Island (40%), 4/14 koalas from the western regions (29%), 2/11 Raymond Island koalas (18%), and 1/13 Cape Otway koalas (8%). There were no cases of oxalate nephrosis identified in the Strzelecki koalas (n = 12). These findings suggest that oxalate nephrosis occurs in koalas from French Island and populations that have received significant influx of koalas from French Island, but not in the Strzelecki region, which has little to no French Island input. This lends support to the theory that an inherited abnormality of oxalate metabolism could underlie the high prevalence of oxalate nephrosis in the Mount Lofty Ranges koala population, and molecular investigations are currently underway to investigate a genetic cause.     

Haematological and biochemical reference values for the koala (Phascolarctos cinereus)

Haematological and biochemical reference values were established from 45 clinically healthy koalas. Statistical analysis revealed no significant differences for sex and season of sampling. Immature koalas had significantly higher alkaline phosphatase and inorganic phosphate values, and significantly lower total protein concentrations due to low globulins values. Enzyme reference values tended to be wide and could limit their usefulness in detecting disease. In the reference values for leukocytes, neutrophils and lymphocytes, the inclusion of low values which were not actually seen may interfere with the detection of reduced levels due to disease.     

Quantitation of meloxicam in the plasma of koalas (Phascolarctos cinereus) by improved high performance liquid chromatography

An improved method to determine meloxicam (MEL) concentrations in koala plasma using reversed phase high performance liquid chromatography equipped with a photo diode array detector was developed and validated. A plasma sample clean-up step was carried out with hydrophilic-lipophilic copolymer solid phase extraction cartridges. MEL was separated from an endogenous interference using an isocratic mobile phase [acetonitrile and 50 mM potassium phosphate buffer (pH 2.15), 45:55 (v:v)] on a Nova-Pak C₁₈ 4-µm (300 × 3.9 mm) column. Retention times for MEL and piroxicam were 8.03 and 5.56 min, respectively. Peak area ratios of MEL to the internal standard (IS) were used for regression analysis of the calibration curve, which was linear from 10 to 1,000 ng/mL (r² > 0.9998). Average absolute recovery rates were 91% and 96% for MEL and the IS, respectively. This method had sufficient sensitivity (lower quantitation limit of 10 ng/mL), precision, accuracy, and selectivity for routine analysis of MEL in koala plasma using 250-µL sample volumes. Our technique clearly resolved the MEL peak from the complex koala plasma matrix and accurately measured MEL concentrations in small plasma volumes.     

An undescribed Demodex sp. and demodicosis in a captive koala (Phascolarctos cinereus).

A 12-yr-old male koala (Phascolarctos cinereus) in a zoo collection developed bilateral, noninflammatory, periocular alopecia. Deep periocular skin scrapings yielded multiple adult, nymphal, and larval mites of a previously undescribed Demodex species. Skin biopsies from affected areas revealed multiple mites in superficial keratin and within hair follicles, associated with a mild intramural lymphocytic folliculitis. Treatment with daily oral ivermectin was safe and effective. Although Demodex sp. are previously reported from skin scrapings in another koala with periocular alopecia, this is the first confirmed case of koala demodicosis.     

Mast cell tumours (mastocytosis) in the horse: A review of the literature and report of 11 cases

Mast cell tumours are uncommon tumours in horses, compared to some other species of domesticated animals. They are most frequently located in the skin, but they can also arise at other sites, including the upper respiratory tract and eye. Cytology or histopathology is required for diagnosis. Treatment options include surgical excision, laser ablation, cryotherapy, intralesional injection of corticosteroids or water, and radiotherapy. Malignant and systemic forms are very rare.