Pharmacokinetics of multiple doses of chloramphenicol in fed adult horses.

To the authors' knowledge, there have been no studies evaluating the pharmacokinetics of chloramphenicol administered orally to horses at the currently recommended dose of 50 mg/kg PO q6 h for multiple days. The published antimicrobial susceptibility breakpoint is 8.0 ug/mL; it is unknown if this concentration is achievable at the recommended dose rate in horses. The aim of this prospective multi-dose pharmacokinetic study was to perform pharmacokinetic analysis of chloramphenicol after multiple doses. The authors hypothesize that the antimicrobial susceptibility breakpoint will not be reached. Seven healthy adult horses were administered 50 mg/kg chloramphenicol base tablets PO q6 h for 4 days. Blood was collected via venipuncture daily at 4 and 6 h after administration for the first 15 doses. After the 16th dose, an IV catheter was aseptically placed in the right jugular vein and blood was collected at regular intervals for pharmacokinetic analysis. Maximum chloramphenicol concentration was variable between horses (2.1-42.7 µg/mL). The highest average chloramphenicol concentration was just below the susceptibility breakpoint at 7.7 ug/mL while the lowest was well below the breakpoint at 1.5 ug/mL. On average, the time above 8.0 µg/mL was 75 min, considerably less than the recommended 50% of the dosing interval. When chloramphenicol is administered at a dose of 50 mg/kg PO q6 h in horses, the highest reliably achievable steady state concentration for at least half of the dosing interval is 2.0 µg/mL. The established susceptibility breakpoint of 8.0 ug/mL is not achievable in adult horses, and should be re-evaluated.

Outcomes after medical and surgical interventions in horses with temporohyoid osteoarthropathy.

BACKGROUND: Temporohyoid osteoarthropathy (THO) is a cause of neurological disease in horses that is characterised by facial and vestibulocochlear nerve deficits. Studies reporting and comparing survival following medical or surgical treatment of THO are lacking. OBJECTIVES: To compare survival and prognosis in horses with THO treated medically or surgically, and to report surgical complications. STUDY DESIGN: Retrospective study. METHODS: The medical records of horses diagnosed with THO were retrieved, and data on signalment, clinical signs and duration, corneal ulceration and bilateral occurrence were recorded. Neurological severity was graded according to clinical signs. Preoperative radiographic and endoscopic images were graded according to the severity of changes. Factors potentially affecting survival and treatment were compared using Cox proportional hazards regression. RESULTS: A total of 77 horses were identified as having THO during the period 1990-2014. Of these, 25 horses underwent ceratohyoid ostectomy (CHO) and eight underwent partial stylohyoid ostectomy (PSHO). Thirteen of 20, one of 25 and one of eight horses treated by medical therapy, CHO and PSHO, respectively, died or were subjected to euthanasia as a consequence of THO. Compared with CHO, medical therapy was significantly associated with nonsurvival, but there were no significant differences in survival between horses undergoing PSHO and medical therapy. The duration of clinical signs, and neurological, radiographic and endoscopic grades were not associated with survival of THO. However, the age of the horse was significantly associated with poorer survival. Survival time was significantly shorter in the medical therapy group compared with the two surgical groups combined, but did not differ significantly between the two surgical groups. No significant difference between groups was seen in the incidence of surgical complications (33.3% in the PSHO and 22.2% in the CHO group). MAIN LIMITATIONS: This was a nonrandomised study of treatment effects on survival and included a low number of cases. CONCLUSIONS: The survival prognosis in horses with THO is good to excellent in those submitted to surgical intervention, and fair in those treated with medical therapy alone.

Pneumonia Caused by Klebsiella spp. in 46 Horses.

BACKGROUND: Klebsiella spp. are implicated as a common cause of bacterial pneumonia in horses, but few reports describe clinical presentation and disease progression. HYPOTHESIS/OBJECTIVES: To describe the signalment, clinicopathologic data, radiographic and ultrasonographic findings, antimicrobial susceptibility, outcome, and pathologic lesions associated with Klebsiella spp. pneumonia in horses. ANIMALS: Forty-six horses from which Klebsiella spp. was isolated from the lower respiratory tract. METHODS: Retrospective study. Medical records from 1993 to 2013 at the William R. Pritchard Veterinary Medical Teaching Hospital, University of California, Davis were reviewed. Exact logistic regression was performed to determine if any variables were associated with survival to hospital discharge. RESULTS: Survival in horses <1 year old was 73%. Overall survival in adults was 63%. For adults in which Klebsiella pneumoniae was the primary isolate, survival was 52%. Mechanical ventilation preceded development of pneumonia in 11 horses. Complications occurred in 25/46 horses, with thrombophlebitis and laminitis occurring most frequently. Multi-drug resistance was found in 47% of bacterial isolates. Variables that significantly impacted survival included hemorrhagic nasal discharge, laminitis, and thoracic radiographs with a sharp demarcation between marked caudal pulmonary alveolar infiltration and more normal-appearing caudodorsal lung. CONCLUSIONS AND CLINICAL IMPORTANCE: Klebsiella spp. should be considered as a differential diagnosis for horses presenting with hemorrhagic pneumonia and for horses developing pneumonia after mechanical ventilation. Multi-drug resistance is common. Prognosis for survival generally is fair, but is guarded for adult horses in which K. pneumoniae is isolated as the primary organism.

Atrial Fibrillation in Eight New World Camelids.

BACKGROUND: There is limited information on the incidence of clinical signs, concurrent illness and treatment options for atrial fibrillation (AF) in New World Camelids (NWC). OBJECTIVE: Describe clinical signs and outcome of AF in NWC. ANIMALS: Eight New World Camelids admitted with AF. METHODS: A retrospective observational study of camelids diagnosed with AF based on characteristic findings on electrocardiogram (ECG). RESULTS: All animals had an irregularly irregular heart rhythm detected on physical examination and 4 cases had obtunded mentation on admission. Three camelids were diagnosed with AF secondary to oleander intoxication, 3 animals had underlying cardiovascular disease, 1 was diagnosed with lone AF and 1 had AF diagnosed on examination for a urethral obstruction. Five of eight animals survived to discharge and nonsurvivors consisted of animals which died or were euthanized as a result of cardiovascular disease (2/8) or extra-cardiac disease unrelated to the AF (1/8). CONCLUSIONS AND CLINICAL IMPORTANCE: Atrial fibrillation occurs in NWC in association with cardiovascular disease, extra-cardiac disease or as lone AF. Amiodarone and transthoracic cardioversion were attempted in one llama with lone AF, but were unsuccessful. Atrial fibrillation was recorded in 0.1% of admissions.

Blood and Cerebrospinal Fluid α-Tocopherol and Selenium Concentrations in Neonatal Foals with Neuroaxonal Dystrophy.

BACKGROUND: Equine neuroaxonal dystrophy/equine degenerative myeloencephalopathy (NAD/EDM) is a neurodegenerative disorder affecting genetically predisposed foals maintained on α-tocopherol (α-TP)-deficient diet. OBJECTIVE: Intramuscular α-TP and selenium (Se) administration at 4 days of age would have no significant effect on serum or cerebrospinal fluid (CSF) α-TP in healthy foals. Serum and CSF α-TP, but not Se, would be significantly decreased in NAD/EDM-affected foals during first year of life. ANIMALS: Fourteen Quarter horse foals; 10 healthy foals supplemented with 0.02 mL/kg injectable α-TP and Se (n = 5) or saline (n = 5) at 4 days of age and 4 unsupplemented NAD/EDM-affected foals. METHODS: Complete neurologic examinations were performed, blood and CSF were collected before (4 days of age) and after supplementation at 10, 30, 60, 120, 180, 240, and 360 days of age. Additional blood collections occurred at 90, 150, 210, and 300 days. At 540 days, NAD/EDM-affected foals and 1 unsupplemented healthy foal were euthanized and necropsies performed. RESULTS: Significant decreases in blood, CSF α-TP and Se found in the first year of life in all foals, with most significant changes in serum α-TP from 4-150 days. Dam α-TP and Se significantly influenced blood concentrations in foals. Injection of α-TP and Se did not significantly increase CSF Se, blood or CSF α-TP in healthy foals. NAD/EDM-affected foals had significantly lower CSF α-TP through 120 days. CONCLUSIONS AND CLINICAL IMPORTANCE: Injection of α-TP and Se at 4 days of age does not significantly increase blood or CSF α-TP. Despite all 14 foals remaining deficient in α-TP, only the 4 genetically predisposed foals developed NAD/EDM.

Quantitative molecular viral loads in 7 horses with naturally occurring equine herpesvirus-1 infection.

REASONS FOR PERFORMING STUDY: Data associating quantitative viral load with severity, clinical signs and survival in equine herpesvirus-1 myeloencephalopathy (EHM) have not been reported. OBJECTIVES: To report the clinical signs, treatment, and temporal progression of viral loads in 7 horses with naturally occurring EHM and to examine the association of these factors with survival. STUDY DESIGN: Retrospective case series. METHODS: The population included 7 horses with EHM presented to the University of California, Davis William R. Pritchard Veterinary Medical Teaching Hospital from May to September 2011. Horses were graded using a neurological grading scale. Daily quantitative PCR was performed on nasal secretions and whole blood. Treatment, survival, outcome and histopathology were reported. RESULTS: At presentation, one horse was neurological grade 5/5, 3 were grade 4/5 and 3 were grade 3/5. All were treated with anti-inflammatory drugs, valacyclovir and management in a sling if necessary. All were infected with equine herpesvirus-1 of DNA polymerase D752 genotype. Peak viral load in nasal secretions and blood of 5 survivors ranged from 6.9 × 10(3) to 2.81 × 10(5) (median 5.11 × 10(4) ) and from 143 to 4340 gB gene copies/million eukaryotic cells (median 3146), respectively. The 2 nonsurvivors presented with grade 3/5 neurological signs and progressed to encephalopathy. Peak viral load was higher in nonsurvivors, with levels in nasal secretions of 1.9 × 10(9) and 2.2 × 10(9) and in blood of 2.05 × 10(4) and 1.02 × 10(5) gB gene copies/million eukaryotic cells. Case fatality was 2/7. CONCLUSIONS: Nonsurvivors had viral loads 1000-fold higher in nasal secretions and 10-fold higher in blood than survivors. There was no relationship between severity of clinical signs at presentation and survival. Thus, encephalopathy and high viral load were negatively associated with survival in this population. Further research should be performed to determine whether high viral loads are associated with encephalopathy and poor prognosis. The Summary is available in Chinese - see Supporting information.