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Abstract

Objective—To determine current practices regarding use of antimicrobials in equine patients undergoing surgery because of colic at veterinary teaching hospitals.

Design—Survey.

Sample Population—Diplomates of the American College of Veterinary Surgeons performing equine surgery at veterinary teaching hospitals in the United States.

Procedure—A Web-based questionnaire was developed, and 85 surgeons were asked to participate. The first part of the survey requested demographic information and information about total number of colic surgeries performed at the hospital, number of colic surgeries performed by the respondent, and whether the hospital had written guidelines for antimicrobial drug use. The second part pertained to nosocomial infections. The third part provided several case scenarios and asked respondents whether they would use antimicrobial drugs in these instances.

Results—Thirty-four (40%) surgeons responded to the questionnaire. Respondents indicated that most equine patients undergoing surgery because of colic at veterinary teaching hospitals in the United States received antimicrobial drugs. Drugs that were used were similar for the various hospitals that were represented, and for the most part, the drugs that were used were fairly uniform irrespective of the type of colic, whereas the duration of treatment varied with the type of colic and the surgical findings. The combination of potassium penicillin and gentamicin was the most commonly used treatment.

Conclusions and Clinical Relevance—Results of this study document the implementation of recommendations by several authors in veterinary texts that antimicrobial drugs be administered perioperatively in equine patients with colic that are undergoing surgery. However, the need for long-term antimicrobial drug treatment in equine patients with colic is unknown. (J Am Vet Med Assoc 2002;220:1359–1365)

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine whether isolation and virulence of Rhodococcus equi from soil and infected foals are associated with clinical disease.

Design—Cross-sectional and case-control study.

Sample PopulationR equi isolates from 50 foals with pneumonia and soil samples from 33 farms with and 33 farms without a history of R equi infection (affected and control, respectively).

ProcedureR equi was selectively isolated from soil samples. Soil and clinical isolates were evaluated for virulence-associated protein antigen plasmids (VapAP) and resistance to the β-lactam antibiotics penicillin G and cephalothin. Microbiologic cultures and VapA-P assays were performed at 2 independent laboratories.

Results—VapA-P was detected in 49 of 50 (98%) clinical isolates; there was complete agreement between laboratories. Rhodococcus equi was isolated from soil on 28 of 33 (84.8%) affected farms and 24 of 33 (72.7%) control farms, but there was poor agreement between laboratories. Virulence-associated protein antigen plasmids were detected on 14 of 66 (21.2%) farms by either laboratory, but results agreed for only 1 of the 14 VapA-P-positive farms. We did not detect significant associations between disease status and isolation of R equi from soil, detection of VapA-P in soil isolates, or resistance of soil isolates to β-lactam antibiotics. No association between β-lactam antibiotic resistance and presence of VapA-P was detected.

Conclusions and Clinical Relevance—On the basis of soil microbiologic culture and VapA-P assay results, it is not possible to determine whether foals on a given farm are at increased risk of developing disease caused by R equi. (J Am Vet Med Assoc 2000;217:220–225)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To evaluate a method of aerobic bacteriologic culture of epidermal collarette specimens from dogs with superficial pyoderma and compare results with those for aerobic bacteriologic culture of abdominal skin specimens in healthy dogs.

Design—Prospective study.

Animals—22 dogs with epidermal collarettes and 24 healthy dogs.

Procedure–Dry sterile cotton swabs were rolled across epidermal collarettes or hairless areas of abdominal skin in healthy dogs and submitted for aerobic bacteriologic culture. Hemolytic colonies of gram-positive–staining cocci were tested for catalase production, and if results were positive, a coagulase test was performed. Colonies with coagulase activity were tested for the ability to ferment mannitol. Antimicrobial susceptibility testing was performed on all Staphylococcus spp that were isolated.

ResultsS intermedius was isolated from collarettes in 18 of 22 dogs with superficial pyoderma but not from healthy dogs. Estimated sensitivity and specificity of the culture method were 81.8% and 100%, respectively. There were no significant differences in the ability to culture S intermedius, the number of S intermedius isolates without resistance to antimicrobials, and the number of S intermedius isolates resistant to penicillin G when comparing dogs with superficial pyoderma for the first time and dogs with recurrent pyoderma, dogs that did or did not receive concurrent antimicrobials, and dogs with and without underlying allergic disease.

Conclusions and Clinical Relevance–Bacteriologic culture of epidermal collarette specimens was a simple and reliable method for identification of S intermedius in dogs with superficial pyoderma, regardless of history of pyoderma or current antimicrobial use. (J Am Vet Med Assoc 2005;226:904–908)

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in Journal of the American Veterinary Medical Association

SUMMARY

Bacampicillin hydrochloride is an ester prodrug that is hydrolyzed to ampicillin after its absorption from the gastrointestinal tract. It was administered intragastrically at a dose rate of 13.5 mg/kg of body weight to ponies and horses, and was highly bioavailable (F = 41.0%), compared with other penicillins in adult horses. The high peak ampicillin plasma concentration of 6,1 ± 0,5 µg/ml achieved and persistence of the antibiotic at concentration of 0.3 ± 0.1 µg/ml 6 hours after its intragastric administration, suggest that bacampicillin hydrochloride may reach suitable bactericidal concentrations for treatment of infections caused by susceptible microorganisms.

In a separate experiment, dichlorvos, an organo-phosphate compound that inhibits some of the esterase activity in plasma, was administered orally to the same animals at a dose rate of 40 mg/kg, followed by intragastric administration of bacampicillin hydrochloride at a dose of 13.5 mg/kg. Plasma pseudocholines-terase and erythrocyte acetylcholinesterase activities were reduced to < 5% of reference (predichlorvos) values after dichlorvos administration. However, rate of hydrolysis of bacampicillin into ampicillin was not affected. Consequently, the disposition and fate of bacampicillin when administered intragastrically 1 day after dichlorvos administration were similar to the values obtained after administration of bacampicillin alone.

Intragastric coadministration of probenecid at a dose rate of 75 mg/kg and bacampicillin at 13.5 mg/ kg limited absorption of the antibiotic from the gastrointestinal tract. This suggests existence of a common transport mechanism for bacampicillin and probenecid in the gastrointestinal wall, and precludes use of this combination for treatment. The bioavailable fraction of ampicillin after combination treatment indicated prolonged residence time in the plasma, presumably as a consequence of reduced renal tubular secretion.

Free access
in American Journal of Veterinary Research

Objective—

To evaluate the decision to test for milk antimicrobial residues in milk from dairy cows treated with procaine penicillin G (PPG).

Design—

Economic-decision analysis after stochastic simulation.

Sample Population—

1,000 computer-simulated cows/model.

Procedure—

Meta-analysis of the Food Animal Residue Avoidance Databank was used to generate PPG disappearance curves for cows given single PPG treatments, IM, of 6,600 U/kg (3,000 U/Ib) of body weight or 26,400 U/kg (12,000 U/lb), and multiple treatments at 26,400 U/kg (12,000 U/lb), IM. These curves were entered into 1,000-replication stochastic pharmacokinetic models, generating population-level milk PPG profiles for each treatment group for each day after treatment, which were subjected to economic-decision analyses of feasibility of residue testing. The model was evaluated for changes in herd size, proportion of herd available for testing, milk production, test price, test sensitivity/specificity, and withdrawal periods.

Results—

For both single-treatment groups, a 2-day withdrawal period avoided violative residues. However, nearly two thirds of the cows risked false identification for violative residues. For the multiple-treated group, nearly 40% had violative residues after a 5-day withdrawal period, and an additional 10 to 15% risked false identification for violative residues. Economic analysis yielded a decision against testing; mean cost was $2 (ie, 5% more than the mean cost of not testing).

Clinical Implications—

Complex dynamics of current milk residue tests discourage practitioners from recommending procedures to clients. In general, increases in herd size, milk production, proportion of a herd available for testing, or milk price will increase the value of testing. Increasing test sensitivity decreases its desirability to producers. (J Am Vet Med Assoc 1997;211:419–427)

Free access
in Journal of the American Veterinary Medical Association

Objective—

To establish the maximum concentration and duration of oxytetracycline residues in milk from cows with retained fetal membranes given the antimicrobial via intrauterine infusion, and to investigate whether the number of infusions or the presence of fever (> 39.7 C) affected the duration of residues.

Design—

Prospective study.

Animals—

54 Holstein cows with retained fetal membranes on a single 1,400-cow commercial dairy.

Procedure—

Cows were treated once a day with 5 g of oxytetracycline (50 ml of 100 mg/ml solution in a povidone base) by intrauterine infusion for at least 2 days, or until the membranes were expelled. Cows that became febrile (rectal temperature > 39.7 C) were also given 20,000 IU of procaine penicillin G/kg of body weight, IM, for 2 to 4 days. Milk samples were collected at 24-hour intervals during treatment, and at 12-hour intervals after the last treatment. All samples were frozen and submitted every 2 weeks for high performance liquid chromatography analysis for oxytetracycline.

Results—

Oxytetracycline was detected in milk of all cows during treatment, at a maximum concentration ranging from 47.2 to 1,804.6 μg/kg (mean, 316.9 μg/kg). Duration of oxytetracycline residues after the last infusion ranged from 0 to 144 hours (mean, 52.3 hours). Neither the number of infusions received, nor development of rectal temperature > 39.7 C, affected the maximum concentration or the duration of oxytetracycline residues in milk.

Clinical Implications—

Milk obtained from cows that had been treated for retained fetal membranes by intrauterine infusion of oxytetracycline should be discarded to avoid illegal residues. (J Am Vet Med Assoc 1996;209:1753–1755)

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in Journal of the American Veterinary Medical Association

SUMMARY

Serum concentrations of metronidazole were determined in 6 healthy adult mares after a single iv injection of metronidazole (15 mg/kg of body weight). The mean elimination rate (K) was 0.23 h-1, and the mean elimination half-life (t1/2) was 3.1 hours. The apparent volume of distribution at steady state was 0.69 L/kg, and the clearance was 168 ml/h/kg.

Each mare was then given a loading dose (15 mg/kg) of metronidazole at time 0, followed by 4 maintenance doses (7.5 mg/kg, q 6 h) by nasogastric tube. Metronidazole concentrations were measured in serial samples of serum, synovia, peritoneal fluid, and urine. Metronidazole concentrations in csf and endometrial tissues were measured after the fourth maintenance dose. The highest mean concentration in serum was 13.9 ± 2.18 μg/ml at 40 minutes after the loading dose (time 0). The highest mean synovial and peritoneal fluid concentrations were 8.9 ± 1.31 μg/ml and 12.8 ± 3.21 μg/ml, respectively, 2 hours after the loading dose. The lowest mean trough concentration in urine was 32 μg/ml. Mean concentration of metronidazole in csf was 4.3 ± 2.51 μg/ml and the mean concentration in endometrial tissues was 0.9 ± 0.48 μg/g at 3 hours after the fourth maintenance dose.

Two mares hospitalized for treatment of bacterial pleuropneumonia were given metronidazole (15.0 mg/kg, po, initially then 7.5 mg/kg, po, q 6 h), while concurrently receiving gentamicin, potassium penicillin, and flunixin meglumine iv. Metronidazole pharmacokinetics and serum concentrations in the sick mares were similar to those obtained in the healthy mares.

Free access
in American Journal of Veterinary Research

Summary

The data on antimicrobials in bob veal calves obtained by USDA-Food Safety Inspection Service (FSIS) during the fiscal year 1988 were reviewed. Of 3,095 calf antibiotic and sulfonamide test (cast)-positive carcass submissions, 967 were chosen by FSIS for antimicrobial residue analyses. Specimens of muscle, liver, and kidney were obtained at abattoirs as a part of the FSIS program, and the results were reviewed by calf submission. At least 1 tissue from each of 425 submissions contained neomycin. Unidentified microbial inhibitors were found in 291 submissions. Streptomycin was found in 86 carcass submissions, penicillin in 81, sulfamethazine in 73, tetracycline HCl in 59, and gentamicin in 53. Other monitored agents were found in < 50 submissions each. Only 257 submissions included evaluation for sulfonamides, but sulfamethazine was found in 28.4% of them. Chloramphenicol was not detected.

Concentrations of neomycin in kidney specimens ranged from 0.25 to > 100 ppm, and differed among the 3 regional laboratories (West, Midwest, and East). The western region had the greatest proportion of low-concentration specimens, whereas the midwestern laboratory had the largest proportion of specimens with very high concentrations (≥ 100 ppm) of neomycin in kidney tissue.

Data to identify the sources and causes of the residues were not available. However, the western laboratory evaluated cast-positive submissions from calves certified to be antimicrobial-free, whereas the other laboratories evaluated submissions from certified and noncertified calves; therefore, this may partially explain regional patterns for neomycin quantities in kidney specimens.

Neomycin predominated among cast-positive verifications. A high prevalence of unidentified microbial inhibitors suggests further identification may be warranted.

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in Journal of the American Veterinary Medical Association

SUMMARY

The effect of bovine mammary secretion during the early nonlactating period and of antibiotic preparations on bovine polymorphonuclear neutrophil (pmn) phagocytic function and morphology were evaluated in a series of in vitro multifactorial experiments. Benzathine cloxacillin (cl), benzathine cephapirin (ce), sodium novobiocin (no), and a combination of dihydrostreptomycin with procaine penicillin G (dp) were prepared in the presence and absence of a peanut oil aluminum monostearate vehicle. The pmn were isolated from bovine blood, and the effect of each antibiotic preparation on pmn function and morphology was evaluated in a buffer, fat, skim, and a combination of fat with skim from bovine mammary secretion during the nonlactating period. The fat and skim were diluted with buffer to approximate their concentration in mammary secretion. Phagocytic functions of pmn were monitored by fluorescent microscopy, which made it possible to estimate both ingestion and intracellular killing of bacteria by pmn. Changes in pmn morphology were monitored by transmission electron microscopy.

The ability of PMN to ingest and kill Staphylococcus aureus ATCC 25923 was significantly decreased by fat, skim, cl, ce, no, and dp. Effects of some antibiotics on ingestion and killing of bacteria by pmn were influenced by the addition of vehicle and by interactions with mammary secretion. Neutrophil morphology was altered by fat, skim, cl, ce, no, and dp. The detrimental effects of cl, ce, no, and dp on pmn morphology were influenced (some significantly) by the presence of vehicle and interactions with mammary secretion. There were significant correlations among secretion- and antibiotic-induced changes in pmn ingestion of bacteria, pmn killing of bacteria, and pmn morphology.

Free access
in American Journal of Veterinary Research

Summary

Despite the high incidence of distal respiratory tract infection of undetermined cause on farms, to our knowledge, the microbiologic effects of conventional antimicrobial treatment for this condition have not been studied. We evaluated the possible pathogenic role of bacterial isolates from the distal airways of foals with clinical respiratory tract disease, by correlating changes in their numbers (increase or decrease) with clinical, endoscopic, and pulmonary cytologic signs of disease resolution during treatment with antimicrobial drugs. We also determined qualitative changes in in vitro antimicrobial susceptibility of bacterial isolates after 7 days of treatment and relapse rate of foals. Significant (P < 0.05) decrease in the numbers of an isolate in the airways was considered strong evidence of a pathogenic role in this disease syndrome. Foals with endoscopically confirmed distal respiratory tract infection (drti; n = 65) were selected at random for treatment (n = 56) or nontreatment (n = 9), and bronchial lavage specimens were cultured and evaluated cytologically before and after 7 days of treatment with trimethoprim-sulfamethoxazole (tms) and a β-lactam drug (penicillin, ampicillin, or sulbactam-ampicillin), the standard treatment in all foals. The effect of treatment was to abruptly reduce the clinical (nasal discharge, cough, adventitious lung sounds) and cytologic signs of airway infection. Severity of disease in nontreated foals, however, did not change or did worsen over time. Reduction in the frequency and numbers of Streptococcus zooepidemicus isolated during treatment supported a causal role for this organism in the clinical syndrome observed. On the other hand, the frequency of non-Str zooepidemicus isolates (eg, Staphylococcus epidermidis, Streptomyces spp, α-hemolytic streptococci) actually increased during treatment, compatible with a commensal or competitive role for these organisms. Significantly (P < 0.001) more pretreatment isolates were susceptible in vitro to either tms or β-lactam drugs than to β-lactam drugs alone; more posttreatment isolates were susceptible to either tms or β-lactam than to either drug alone. These data indicate that there may be some benefit to combined use of tms plus β-lactam drugs in foals with drti. Mean ± sem relapse rate was 31 ± 6% (range 0 to 57%); risk factors (clinical signs of disease, laboratory variables) for relapse could not be identified. In conclusion, treatment resulted in significant (P < 0.001) reduction in airway inflammation in foals with clinical drti. The high reinfection rate indicates that a predisposing factor, possibly age-related immunodeficiency, may predispose foals to illness and persists after treatment.

Free access
in American Journal of Veterinary Research