Eight Holstein cows, 4 inoculated intracisternally in 1 quarter of the mammary gland with Escherichia coli and 4 noninfected controls, were administered ceftiofur sodium (3 mg/kg of body weight, IV, q 12 hours) for 24 hours, beginning at 14 hours after inoculation of infected cows. All challenge-exposed cows became infected, with mean +/-SEM peak log10 bacterial concentration in milk of 5.03 +/-0.69 colony-forming units/ml. The infection resulted in systemic signs (mean peak rectal temperature, 41.5 +/- 0.3 C; anorexia; signs of depression) and local inflammation (mean peak albumin concentration in milk, 7.89 +/- 1.71 mg/ml). Ceftiofur was detectable in milk from all challenge-exposed cows, compared with only 1 of 4 noninfected cows, and the mean period after inoculation that ceftiofur was detectable in milk was longer (P < 0.05) in infected (147.7 +/- 27.5 hours) than noninfected cows (1.3 +/- 1.3 hours). However, maximal ceftiofur concentration attained in milk for all cows was 0.28 micrograms/ml, and was 0.20 micrograms/ml or less for all but 2 milk samples collected for 10 days after challenge exposure. Mean serum concentration of ceftiofur peaked at 1.0 +/- 0.3 micrograms/ml and 0.7 +/- 0.1 micrograms/ml for infected and noninfected COWS, respectively. After each ceftiofur dose, mean peak and trough concentrations of ceftiofur in serum did not differ between groups; however, concentration of ceftiofur in serum was higher at 7 hours after each dose in noninfected cows, suggesting more rapid clearance of the drug in infected cows. Ceftiofur was not detected in serum (< 0.05 micrograms/ml) of any cow at or after 120 hours following inoculation of infected cows Storage of serum samples at -20 C for 3 weeks resulted in a 98.8% decrease in ceftiofur activity, compared with that in fresh serum samples. Eighty-seven percent of this loss occurred 30 minutes after mixing serum and ceftiofur; thus, about 13% of the original activity was lost in storage.

Ceftiofur hydrochloride was tested for effectiveness against induced colibacillosis in neonatal swine. In this model, pigs < 12 hours old were inoculated via stomach tube with a virulent, K99+, nalidixic acid-resistant strain of Escherichia coli. Six hours after challenge exposure, 1 dose of ceftiofur was administered either IM or orally in experiment 1 and orally only in experiment 2. Mortality, shedding of bacteria, fecal consistency scores, and body weight changes were monitored for 10 days. In experiment 1 (n = 383 pigs), all treatments at dosage that ranged between 0.5 and 64.0 mg of ceftiofur/kg of body weight significantly (P < 0.001) reduced mortality, bacterial shedding, and diarrhea and increased weight gain, compared with findings in untreated controls. There were no detectable differences between oral and IM routes, except that there was greater reduction in bacteria shedding associated with the oral route of administration. In experiment 2 (n = 505 pigs), ceftiofur was administered orally either once at 6 hours after challenge exposure or twice at 6 and at 48 hours after the first dose. Dosage of ceftiofur was 0, 5, 10, 20, 30, or 60 mg/kg administered once, or half the same dose was administered at each of 2 times. At the optimal dosage (10 mg/kg), a single dose was as effective as 2 doses. The single administration at all dosages reduced mortality, bacterial shedding, and diarrhea scores and increased body weight gain, compared with findings in untreated pigs (P < 0.01). In this induced infection model, the optimal treatment dosage was determined to be 10 mg/kg administered once.

Objective: To determine the prevalence of selected virulence genes and the antimicrobial susceptibility of multidrug-resistant (MDR) Escherichia coli isolated from diarrheic neonatal calves. Sample: 97 E coli isolates from diarrheic neonatal calves. Procedures: E coli isolates were tested via PCR assay for 6 virulence genes and susceptibility to 17 drugs belonging to 9 classes. A 2-sample test of proportions was used to make comparisons between proportions of virulent and avirulent MDR isolates. Results: 23 of 97 (23.7%) isolates were virulent, and 74 (76.3%) were avirulent. Of the 23 virulent isolates, 15 (65.2%) were positive for K99, 14 (60.9%) for F41, 12 (52.2%) for STa, 9 (39.1%) for Stx1, 6 (26.1%) for intimin, and 0 (0%) for Stx2. Twenty of 23 (87.0%) virulent isolates expressed ≥ 2 virulence genes, and 3 of 23 (13.0%) were positive for 1 virulence factor. Eight of 23 (34.8%) virulent isolates expressed STa, K99, and F41, whereas 1 of 23 (4.4%) was positive for STa, F41, intimin, and Stx1. The second most frequent gene pattern was Stx1 and intimin. Twenty of 23 (87.0%) virulent isolates were MDR; the highest prevalence of resistance was recorded for the macrolide-lincosides, followed by the tetracyclines and penicillins. Also, 17 of 23 (74.0%) virulent isolates were resistant to sulfadimethoxine, and 10 of 23 (43.5%) were resistant to trimethoprim-sulfamethoxazole. Additionally, 60 of 74 (81.0%) avirulent isolates were MDR. Conclusions and Clinical Relevance: The prevalence of multidrug resistance was comparable for virulent and avirulent E coli isolated from diarrheic neonatal calves. Cephalosporins and aminoglycosides had reasonable susceptibility.

Eight Holstein cows, 4 inoculated intracisternally in 1 quarter of the mammary gland with Escherichia coli and 4 noninfected controls, were administered ceftiofur sodium (3 mg/kg of body weight, IV, q 12 hours) for 24 hours, beginning at 14 hours after inoculation of infected cows. All challenge-exposed cows became infected, with mean +/- SEM peak log10 bacterial concentration in milk of 5.03 +/- 0.69 colony-forming units/ml. The infection resulted in systemic signs (mean peak rectal temperature, 41.5 +/- 0.3 C; anorexia; signs of depression) and local inflammation (mean peak albumin concentration in milk, 7.89 +/- 1.71 mg/ml). Ceftiofur was detectable in milk from all challenge-exposed cows, compared with only 1 of 4 noninfected cows, and the mean period after inoculation that ceftiofur was detectable in milk was longer (P < 0.05) in infected (147.7 +/- 27.5 hours) than noninfected cows (1.3 +/- 1.3 hours). However, maximal ceftiofur concentration attained in milk for all cows was 0.28 micrograms/ml, and was 0.20 micrograms/ml or less for all but 2 milk samples collected for 10 days after challenge exposure. Mean serum concentration of ceftiofur peaked at 1.0 +/- 0.3 micrograms/ml and 0.7 +/- 0.1 micrograms/ml for infected and noninfected COWS, respectively. After each ceftiofur dose, mean peak and trough concentrations of ceftiofur in serum did not differ between groups; however, concentration of ceftiofur in serum was higher at 7 hours after each dose in noninfected cows, suggesting more rapid clearance of the drug in infected cows. Ceftiofur was not detected in serum (< 0.05 micrograms/ml) of any cow at or after 120 hours following inoculation of infected cows. Storage of serum samples at -20 C for 3 weeks resulted in a 98.8% decrease in ceftiofur activity, compared with that in fresh serum samples. Eighty-seven percent of this loss occurred 30 minutes after mixing serum and ceftiofur; thus, about 13% of the original activity was lost in storage. Storage of milk samples under similar conditions did not result in loss of ceftiofur activity. Despite acute inflammation, the dosage of ceftiofur used in this trial would not result in drug concentrations in milk above FDA safe concentrations, or above the reported minimum inhibitory concentration for coliform bacteria.

The minimal inhibitory concentration (MIC) of cefixime, a new third-generation orally administered caphalosporin, was determined for reference and clinical isolates from dogs. The MIC of the drug for all but 1 of the 18 Enterobacteriaceae isolates tested, 1 Pasteurella canis, 1 Rhodococcus equi, 1 Streptococcus canis, and 1 Streptococcus group G isolate, was less than 1.0 micrograms/ml. The MIC for 9 Staphylococcus intermedius isolates ranged from 1.56 to 6.25 micrograms/ml and, for 8 Sta aureus isolates, the MIC values ranged from 1.56 to 12.5 micrograms/ml. Pseudomonas aeruginosa, Actinomyces sp, and a single Bordetella bronchiseptica isolate were considered resistant to cefixime. Cefixime was administered orally in 2 phases at a standard dosage of 5 mg/kg of body weight to clinically normal adult male and female dogs. In the first phase, the drug was given once as a capsule and once as a suspension. In the second phase, it was administered once per day for 6 consecutive days in capsule form. Serum drug concentration was determined by use of a microbiological assay, and the following kinetic values were estimated for each dog: area under the concentration-time curve, peak serum drug concentration (Cmax), time of Cmax, absorption half-life, and elimination half-life (t1/2el). The kinetic profile of the drug in serum after oral administration of a single dose of cefixime was similar, with mean Cmax values of 3.36 and 4.76 micrograms/ml after treatment with the capsule and suspension, respectively. Quick oral absorption is characteristic for cefixime in dogs; mean absorption half-life values of 1.3 and 0.58 hours for the capsule and suspension, respectively, were calculated. Drug elimination from serum was biphasic, with an initial mean t1/2el of 8.1 to 8.6 hours and a secondary mean t1/2el of 11.7 to 14.5 hours. In the trial involving once daily treatment for 6 days, serum drug concentration after the sixth dose was significantly (P < 0.05) higher than that after the first dose. indicating drug accumulation. Cefixime is extensively bound to canine serum proteins (82 to 92% at concentration ranging between 7.5 and 1.5 micrograms/ml). Concentration of cefixime was determined in the uterus, ovaries, and abdominal fat tissues 24 hours after single-dose treatment and 24 hours after the sixth treatment. Tissue drug distribution was limited after administration of the single dose, but improved after the sixth dose. The in vitro antibacterial activity of the drug and its pharmacokinetic properties warrant assessing its clinical and bacteriologic efficacy as a longterm once-daily orally administered treatment for common bacterial infections in dogs.

The susceptibility of 50 clinical Escherichia coli isolates to various antibacterials, including cefoxitin and cefotetan was ascertained, and the minimal inhibitory concentration (MIC) of cefoxitin and cefotetan for each of these isolates was determined. The pharmacokinetics of cefoxitin and cefotetan after a single IV or SC injection (30 mg/kg of body weight) were determined in 4 dogs. Of the 50 E coli isolates, 98% were susceptible in vitro to cefotetan, 90% were susceptible to cefoxitin, and 88% were susceptible to gentamicin. The MIC that would inhibit the growth of 90% of the E coli isolates (MIC90) was 0.25 micrograms/ml for cefotetan and 4 micrograms/ml for cefoxitin. Plasma cefotetan concentrations remained above MIC90 for (mean SD) 8.2 +/- 1.72 hours and 13.52 +/- 0.28 hours after IV and SC administration, respectively. Plasma cefoxitin concentrations remained above MIC90 for (mean +/- SD) 5.37 +/- 1.18 hours and 7.95 +/- 0.71 hours after IV and SC administration, respectively. We concluded that cefotetan was superior to cefoxitin in activity against E coli in vitro. We recommend that cefotetan be given at a dosage of 30 mg/kg, IV, every 8 hours, or SC, every 12 hours.

Twenty-nine healthy 17- to 29-day-old unweaned Isaeli-Friesian male calves were each given a single IV or IM injection of 10 or 20 mg of moxalactam disodium/kg of body weight. Serum concentrations were measured serially during a 12-hour period. Serum concentration vs time profiles were analyzed by use of linear least-squares regression analysis and the statistical moment theory. The elimination half-lives after IV administration were 143.7 +/- 30.2 minutes and 155.5 +/- 10.5 minutes (harmonic mean +/ SD) at dosages of 10 and 20 mg of moxalactam/kg of body weight, respectively. Corresponding mean residence time values were 153.1 +/- 26.8 minutes and 169.9 +/- 19.3 minutes (arithmetic mean +/- SD). Mean residence time values after IM administration were 200.4 +/- 17.5 minutes and 198.4 +/- 19.9 minutes at dosages of 10 and 20 mg/kg, respectively. The volumes of distribution at steady state were 0.285 +/- 0.073 L/kg and 0.313 +/- 0.020 L/kg and total body clearance values were 1.96 +/- 0.69 ml/min/kg and 1.86 +/- 0.18 ml/min/kg after administration of dosages of 10 and 20 mg/kg, respectively. Moxalactam was rapidly absorbed from the IM injection site and peak serum concentrations occurred at 1 hour. The estimated bioavailability ranged from 69.8 to 79.1%. The amount of serum protein binding was 53.4, 55.0, and 61.5% when a concentration of moxalactam was at 50, 10, and 2 micrograms/ml respectively. The minimal inhibitory concentrations of moxalactam ranged from 0.01 to 0.2 micrograms/ml against Salmonella and Escherichia coli strains and from 0.005 to 6.25 micrograms/ml against Pasteurella multocida strains.

Ceftazidime pharmacokinetic values were studied in unweaned calves given the antibiotic alone or in combination with probenecid. Ceftazidime was administered IV to 9 calves at a dosage of 10 mg/kg of body weight and IM (10 mg/kg) to 8 calves, to 7 calves (10 mg/kg plus probenecid [40 mg/kg]), and to 9 calves (10 mg/kg plus probenecid [80 mg/kg]). Serum concentration-vs-time data were analyzed, using noncompartmental methods based on statistical moment theory. The data for IV ceftazidime administration also were fitted by use of a linear, open 2-compartment model. The mean (+/- SD) terminal half-life was 138.7 +/- 23.6 minutes and 126.3 +/- 10.5 minutes after IV and IM administrations, respectively. The mean residence time was 167.3 +/- 21.1 minutes and 201.4 +/- 16.8 minutes after IV and IM administrations, respectively. Coadministration of probenecid did not affect the terminal half-life or mean residence time values. The total body clearance was 1.75 +/- 0.26 ml/min/kg, and the volume of distribution at steady state was 0.294 +/- 0.064 L/kg. The estimated mean absorption time was 34.1 minutes. There were no significant differences between the mean residence time calculated by statistical moment theory or by compartmental analysis, indicating central compartment output of ceftazidime. The 90% minimal inhibitory concentration values of ceftazidime determined for Escherichia coli, Salmonella spp, Pasteurella multocida, and P haemolytica isolates ranged from less than 0.01 to 0.1 microgram/microliter.