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Abstract

Objective—To determine whether foals with pneumonia that were treated with erythromycin, alone or in combination with rifampin or gentamicin, had a higher risk of developing adverse effects, compared with foals treated with trimethoprim-sulfamethoxazole (TMS), penicillin G procaine (PGP), or a combination of TMS and PGP (control foals).

Design—Retrospective study.

Animals—143 foals < 240 days old.

Procedure—Information on age, sex, breed, primary drug treatment, total days of treatment with the primary drug, and whether the foal developed diarrhea, hyperthermia, or respiratory distress was obtained from the medical records. Relative risk (RR) and attributable risk (AR) were calculated to compare risk of adverse reactions between foals treated with erythromycin and control foals.

Results—Only 3 (4.3%) control foals developed diarrhea; none developed hyperthermia or respiratory distress. Foals treated with erythromycin had an 8-fold risk (RR, 8.3) of developing diarrhea, compared with control foals, and increased risks of hyperthermia (AR, 25%) and respiratory distress (AR, 15%).

Conclusion and Clinical Relevance—Results suggest that use of erythromycin to treat foals with pneumonia was associated with an increased risk of diarrhea, hyperthermia, and respiratory distress, compared with use of TMS or PGP. (J Am Vet Med Assoc 2000;217:68–73)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine disposition kinetics of amikacin in neonatal foals administered high doses at extended intervals.

Animals—7 neonatal foals.

Procedure—Amikacin was administered (21 mg/kg, IV, q 24 h) for 10 days. On days 1, 5, and 10, serial plasma samples were obtained for measurement of amikacin concentrations and determination of pharmacokinetics.

Results—Mean ± SD peak plasma concentrations of amikacin extrapolated to time 0 were 103.1 ± 23.4, 102.9 ± 9.8, and 120.7 ± 17.9 µg/mL on days 1, 5, and 10, respectively. Plasma concentrations at 1 hour were 37.5 ± 6.7, 32.9 ± 2.6, and 30.6 ± 3.5 µg/mL; area under the curve (AUC) was 293.0 ± 61.0, 202.3 ± 40.4, and 180.9 ± 31.2 (µg · h)/mL; elimination half-life (t1/2β) was 5.33, 4.08, and 3.85 hours; and clearance was 1.3 ± 0.3, 1.8 ± 0.4, and 2.0 ± 0.3 mL/(min · kg), respectively. There were significant increases in clearance and decreases in t1/2β, AUC, mean residence time, and plasma concentrations of amikacin at 1, 4, 8, 12, and 24 hours as foals matured.

Conclusions and Clinical Relevance—Once-daily administration of high doses of amikacin to foals resulted in high peak plasma amikacin concentrations, high 1-hour peak concentrations, and large values for AUC, consistent with potentially enhanced bactericidal activity. Age-related findings suggested maturation of renal function during the first 10 days after birth, reflected in enhanced clearance of amikacin. High-dose, extended-interval dosing regimens of amikacin in neonatal foals appear rational, although clinical use remains to be confirmed. (Am J Vet Res 2004;65:473–479)

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in American Journal of Veterinary Research

Abstract

Objective—To determine effects of prior feeding on pharmacokinetics and estimated bioavailability of orally administered microencapsulated erythromycin base (MEB) in healthy foals.

Animals—6 healthy foals, 3 to 5 months old.

Procedure—Foals were given 2 doses of MEB (25 mg/kg of body weight, PO). One dose was administered after food was withheld overnight, and the other was administered after foals had consumed hay. The study used a crossover design with a 2-week period between doses. Blood was collected via a jugular vein prior to and at specific times after drug administration. Concentrations of erythromycin A and anhydroerythromycin A in plasma were determined, using highperformance liquid chromatography. Results pharmacokinetic analysis of plasma concentration-time data for food-withheld and fed conditions were compared.

Results—Plasma concentrations of erythromycin A for foals were lower after feeding than concentrations when food was withheld. Area under the plasma concentration- time curve, maximum plasma concentration, and estimated bioavailability were greater in foals when food was withheld than when foals were fed. Anhydroerythromycin A was detected in plasma after administration of MEB in all foals.

Conclusions and Clinical Relevance—Foals should be given MEB before they are fed hay. Administration of MEB to foals from which food was withheld overnight apparently provides plasma concentrations of erythromycin A that exceed the minimum inhibitory concentration of Rhodococcus equi for approximately 5 hours. The dosage of 25 mg/kg every 8 hours, PO, appears appropriate. (Am J Vet Res 2000;61:1011–1015)

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in American Journal of Veterinary Research

Abstract

Objective—To determine pharmacokinetics and plasma concentrations of erythromycin and related compounds after intragastric administration of erythromycin phosphate and erythromycin estolate to healthy foals.

Animals—11 healthy 2- to 6-month-old foals.

Procedure—Food was withheld from foals overnight before intragastric administration of erythromycin estolate (25 mg/kg of body weight; n = 8) and erythromycin phosphate (25 mg/kg; 7). Four foals received both drugs with 2 weeks between treatments. Plasma erythromycin concentrations were determined at various times after drug administration by use of high-performance liquid chromatography. Maximum plasma peak concentrations, time to maximum concentrations, area under plasma concentration versus time curves, half-life of elimination, and mean residence times were determined from concentration versus time curves.

Results—Maximum peak concentration of erythromycin A after administration of erythromycin phosphate was significantly greater than after administration of erythromycin estolate (2.9 ± 1.1 µg/ml vs 1.0 ± 0.82 µg/ml). Time to maximum concentration was shorter after administration of erythromycin phosphate than after erythromycin estolate (0.71 ± 0.29 hours vs 1.7 ± 1.2 hours). Concentrations of anhydroerythromycin A were significantly less 1 and 3 hours after administration of erythromycin estolate than after administration of erythromycin phosphate.

Conclusions and Clinical Relevance—Plasma concentrations of erythromycin A remained > 0.25 µg/ml (reported minimum inhibitory concentration for Rhodococcus equi) for at least 4 hours after intragastric administration of erythromycin phosphate or erythromycin estolate, suggesting that the recommended dosage for either formulation (25 mg/kg, q 6 h) should be adequate for treatment of R equi infections in foals. (Am J Vet Res 2000;61:914–919)

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in American Journal of Veterinary Research

Abstract

Objective—To evaluate the efficacy and safety of intra-articular administration of ethyl alcohol for arthrodesis of tarsometatarsal joints in horses.

Animals—8 healthy female horses without lameness or radiographic evidence of tarsal joint osteoarthritis.

Procedure—In each horse, 1 tarsometatarsal joint was treated with 4 mL of 70% ethyl alcohol and the opposite joint was treated with 4 mL of 95% ethyl alcohol. Lameness examinations were performed daily for 2 weeks, followed by monthly evaluations for the duration of the 12-month study. Radiographic evaluations of both tarsi were performed 1 month after injection and every 3 months thereafter. Gross and histologic examinations of the tarsi were undertaken at completion of the study.

Results—Horses had minimal to no lameness associated with the treatments. Radiography revealed that 8 of 16 joints were fused by 4 months after treatment, with significantly more joints fused in the 70% ethyl alcohol group. Fifteen of 16 joints were considered fused at postmortem examination at 12 months. Gross and histologic examinations revealed foci of dense mature osteonal bone spanning the joint spaces. Bony fusion appeared to be concentrated on the dorsolateral, centrolateral, and plantarolateral aspects of the joints. Significant differences were not detected between treatment groups for lameness or pathologic findings.

Conclusions and Clinical Relevance—Administration of ethyl alcohol into the tarsometatarsal joint of healthy horses appeared to facilitate arthrodesis of the joint in a pain-free manner. Results warrant further investigation into the potential use of ethyl alcohol in horses clinically affected with osteoarthritis of the tarsometatarsal and distal intertarsal joints.

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in American Journal of Veterinary Research

Abstract

Objective—To determine the bacterial, fungal, and endotoxin concentrations in aerosolized ambient air during the winter and summer in feedyards located in the Southern High Plains, identify aerosolized microbial pathogens, and determine the size of microbial and dust components.

Sample Population—Aerosol samples were obtained from 7 feedyards.

Procedure—Aerosol samples were collected upwind, on-site, and downwind from each feedyard at a point 1 m above the ground by use of biological 2- and 6- stage cascade impactors.

Results—Significantly more microbes were cultured from on-site and downwind samples than upwind samples. There were significantly more microbes during the summer than during the winter. However, mean endotoxin concentration was significantly higher during the winter (8.37 ng/m3) than the summer (2.63 ng/m3). Among 7 feedyards, mean ± SE number of mesophilic bacteria (1,441 ± 195 colony-forming units [CFUs]/m3) was significantly higher than mean number of anaerobic bacteria (751 ± 133 CFUs/m3) or thermophilic bacteria (54 ± 10 CFUs/m3) in feedyard air. Feedyard aerosol samples contained more mesophilic fungi (78 ± 7 CFUs/m3) than thermophilic fungi (2 ± 0.2 CFUs/m3). Eighteen genera of bacteria were identified by use of an automated identification system.

Conclusions and Clinical Relevance—It appeared that gram-negative enteric pathogens offered little risk to remote calves or humans via ambient aerosols and that gram-positive pathogens of the Bacillus, Corynebacterium, and Staphylococcus spp can be spread by aerosols in and around feedyards. It was common to detect concentrations of endotoxin in the ambient air of 7 feedyards. ( Am J Vet Res 2004; 65:45–52)

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in American Journal of Veterinary Research

Abstract

Objective—To determine clinical signs, results of diagnostic testing, and outcome in horses with internal Corynebacterium pseudotuberculosis infection.

Design—Retrospective study.

Animals—30 horses.

Procedure—Information pertaining to clinical data, results of diagnostic tests, and costs of hospitalization and treatment was extracted from medical records of affected horses.

Results—Internal C pseudotuberculosis infection was diagnosed on the basis of clinical signs, diagnostic imaging, and clinicopathologic data, including results of serologic tests and bacterial culture. The most common clinical signs were concurrent external abscesses, anorexia, fever, lethargy, weight loss, and signs of respiratory tract disease or abdominal pain. Clinicopathologic abnormalities included a geometric mean reciprocal serum synergistic hemolysin inhibition titer ≥ 512, leukocytosis with neutrophilia, hyperglobulinemia, hyperfibrinogenemia, and anemia. Specific organ involvement was diagnosed in 27 of 30 horses. Affected organs included the liver (18 horses), lungs (12), kidneys (7), and spleen (3); multiple organs were affected in 10 horses. Treatment with antimicrobials for a median of 36 days (range, 7 to 97 days) was usually successful, yielding an overall survival rate of 71%.

Conclusions and Clinical Relevance—Early diagnosis and long-term antimicrobial treatment were important for a successful outcome in horses with internal C pseudotuberculosis infection. Ultrasonographic imaging was an important technique for identifying specific organs affected, aiding in obtaining samples for a definitive diagnosis, and monitoring response to treatment. Pregnant mares with internal infections are at risk for fetal loss. Preexisting chronic organ disease may be associated with a poor prognosis. (J Am Vet Med Assoc 2005;227:441–448)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine gene transcription for cytokines in nucleated cells in CSF of horses without neurologic signs or with cervical stenotic myelopathy (CSM), West Nile virus (WNV) encephalitis, equine protozoal myeloencephalitis (EPM), or spinal cord trauma.

Animals—41 horses (no neurologic signs [n = 12], CSM [8], WNV encephalitis [9], EPM [6], and spinal cord trauma [6]).

Procedures—Total RNA was extracted from nucleated cells and converted into cDNA. Gene expression was measured by use of real-time PCR assay and final quantitation via the comparative threshold cycle method.

Results—Cytokine genes expressed by nucleated cells of horses without neurologic signs comprised a balance between proinflammatory tumor necrosis factor-α (TNF-α), anti-inflammatory cytokines (interleukin [IL]-10 and transforming growth factor [TGF]-β), and Th1 mediators (interferon [IFN]-γ). Cells of horses with CSM mainly expressed genes for TNF-α, TGF-β, and IL-10. Cells of horses with WNV encephalitis mainly expressed genes for IL-6 and TGF-β. Cells of horses with EPM mainly had expression of genes for IL-6, IL-8, IL-10, TNF-α, IFN-γ, and TGF-β. Cells from horses with spinal cord trauma had expression mainly for IL-6; IFN-γ; TGF-β; and less frequently, IL-2, IL-10, and TNF-α. Interleukin-8 gene expression was only detected in CSF of horses with infectious diseases.

Conclusions and Clinical Relevance—Despite the small number of CSF samples for each group, results suggest distinct gene signatures expressed by nucleated cells in the CSF of horses without neurologic signs versus horses with inflammatory or traumatic neurologic disorders.

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in American Journal of Veterinary Research
in Journal of the American Veterinary Medical Association

Abstract

Objective—To describe clinical manifestations of cutaneous and ocular habronemiasis in horses and evaluate outcome of treatment.

Design—Retrospective study.

Animals—63 horses.

Procedure—The diagnosis was made on the basis of history, clinical signs, and identification of calcified concretions (sulfur granules) in lesions. Histologic examination of biopsy specimens was used to confirm the diagnosis. Case horses were compared with a control population of 12,720 horses examined during the same period.

Results—Arabians, gray horses, and horses with diluted coat colors were overrepresented; Thoroughbreds were underrepresented. Lesions were identified most often during the summer and early fall. The medial canthus of the eye, male genitalia, third eyelid, and distal portions of the extremities were the most commonly affected locations. Twenty-five lesions were biopsied, and results of histologic examination were consistent with a diagnosis of habronemiasis. However, nematode larvae were seen in only 11 (44%) biopsy specimens. Treatment consisted of surgical removal (7 horses) or medical treatment (56) consisting of debulking granulation tissue and topical, intralesional, or systemic treatment with corticosteroids. All horses were treated with ivermectin.

Conclusions and Clinical Relevance—Results suggest that cutaneous and ocular habronemiasis should be considered when examining a horse during the summer months with a proliferative, moist, granulomatous lesion. Treatment should be aimed at decreasing the size of the lesion, reducing inflammation, and preventing recurrence. In general, the prognosis was good, and healing occurred within a few weeks. Fly control and regular deworming with ivermectin are recommended to reduce the incidence of habronemiasis. (J Am Vet Med Assoc 2003;222: 978–982)

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in Journal of the American Veterinary Medical Association