Clinical pharmacokinetics of five oral cephalosporins in calves

Modification of empirical antimicrobial regimens in large animal medicine

BACKGROUND

Empirical antimicrobial regimens can be modified following new diagnostic information or when empirical treatment fails. Little is known about the frequency or clinical context in which these modifications occur. We characterised these modifications in a large animal hospital to identify when antimicrobial use could be optimised.

METHODS

Chart reviews were performed for all inpatients and outpatients administered antimicrobials at a large animal veterinary referral and teaching hospital in 2017-2018 (n=1163 visits) to determine when and why empirical regimens were modified. Multinomial logistic regression was performed to identify factors associated with reasons for modification.

RESULTS

Empirical antimicrobial regimens were modified in 17.3 per cent of visits. The main reasons were parenteral-oral conversions in horses and failure of disease prevention or treatment in ruminants. Empirical therapy for disease prevention was more likely to be modified because of complications in ruminants and in animals on the emergency/critical care service. Empirical therapy for disease treatment was more often modified for reasons other than de-escalation in ruminants and in animals with longer lengths of stay.

CONCLUSIONS

Empirical antimicrobial regimens were modified infrequently and mostly for purposes of parenteral-oral conversion in horses and lack of response in ruminants. De-escalation of antimicrobials administered for disease treatment, when guided by diagnostics, is a major tenet of judicious antimicrobial use. However, more research is needed to determine when and how antimicrobial regimens administered for disease prevention should be modified.

Ceftiofur pharmacokinetics in Nile tilapia Oreochromis niloticus after intracardiac and intramuscular administrations

Ceftiofur is a broad-spectrum third generation cephalosporin, which acts by inhibiting bacterial cell wall synthesis. It is active against Gram-positive and Gram-negative bacteria such as Aeromonas hydrophila and β-lactamase-producing strains, which are common pathogens in freshwater fish. Ceftiofur pharmacokinetics in Nile tilapia Oreochromis niloticus were studied following single intracardiac (i.c.) or intramuscular (i.m.) administration of ceftiofur sodium (NAXCEL®) in a dose of 5 mg ceftiofur kg-1 body weight. After i.c. injection, ceftiofur plasma concentrations decreased biexponentially, suggesting a 2-compartmental open model. Distribution and elimination half-lives (t0.5(α) and t0.5(β)) were 0.61 ± 0.22 and 0.14 ± 0.03 h mean ±SD, respectively. Elimination constant (Kel) and total body clearances (Cltot) were 3.22 ± 0.48 h-1 and 1.64 ± 0.47 l h-1 kg-1, respectively. Volume of distribution (Vss) and areas under curves (AUC) were 0.12 ± 0.03 l kg-1 and 24.18 ± 8.81 µg ml-1 h, respectively. Following i.m. injection of ceftiofur, plasma concentrations were best described by a 1-compartment open model with a first order absorption; bioavailability was quite high (96.85 ± 23.74%). Plasma maximum concentration (Cmax) was 12.32 ± 6.53 µg ml-1; achieved at time of maximum concentration (Tmax) of 0.74 ± 0.04 h. Absorption and elimination half-lives (t0.5ab and t0.5β) were 0.49 ± 0.06 and 0.53 ± 0.03 h, respectively. In conclusion, i.m. injection of ceftiofur sodium produced extremely high bioavailability with high plasma concentrations that persisted up to 6 h post injection, which may make ceftiofur a useful alternative antibiotic for treatment of brood stock or important ornamental fishes.

Absorption kinetics and bioavailability of cephalexin in the dog after oral and intramuscular administration

The pharmacokinetics of cephalexin, a first generation cephalosporin, were investigated in dogs using two formulations marketed for humans, but also often employed by practitioners for pet therapy. Cephalexin was administered to five dogs intravenously and intramuscularly as a sodium salt and by the oral route as a monohydrate. The dosage was always 20 mg/kg of active ingredient. A microbiological assay with Sarcina lutea as the test organism was adopted to measure cephalexin concentrations in serum. The mean residence time (MRT) median values after intravenous (i.v.), intramuscular (i.m.) and oral administration (p.o.) were 86 min, 200 min, and 279 min, respectively. After i.m. and oral dosing the peak serum concentrations (24.2 +/- 1.8 micrograms/mL and 20.3 +/- 1.7 micrograms/mL, respectively) were attained at 90 min in all dogs and bioavailabilities were 63 +/- 10% and 57 +/- 5%, respectively. The time course of the cephalexin serum concentrations after oral administration was best described by a model incorporating saturable absorption kinetics of the Michaelis-Menten type: thus in the gastrointestinal tract of dogs a carrier mediated transport for cephalexin similar to that reported in humans, may exist. The predicted average serum concentrations of cephalexin after repeated i.m. and oral administration indicated that, in order to maintain the therapeutic concentrations, the 20 mg/kg b.w. dosage should be administered every 6-8 h.

Age-related differences in norfloxacin pharmacokinetic behaviour following intravenous and oral administration in sheep

The pharmacokinetics of norfloxacin after intravenous (i.v.) and oral (PO) administration in lambs (n = 5) and adult sheep (n = 5) were studied. After i.v. administration (10 mg.kg-1) plasma concentrations were best fitted by a three-compartment open model in both age groups. Distribution volumes were significantly larger in lambs (approximate 4.0 fold difference between 4 week old and adult sheep). There was no significant difference (p < 0.05) between the groups in terms of elimination halflife but plasma clearance was significantly higher in lambs. Norfloxacin was poorly absorbed after oral administration (60 mg.kg-1) in sheep (F = 4.04%). Mean oral bioavailability was 73.51% in lambs (30 mg.kg-1). Norfloxacin elimination was faster in lambs after oral administration. MRTt was significantly prolonged in both age groups when compared with the respective data for i.v. administration.

Contrast between the pharmacokinetics of two formulations of cephalexin after intramuscular administration in cattle

Two commercial formulations of cephalexin were administered intramuscularly to five heifers and five bulls in a balanced crossover design. Statistically significant and clinically important differences were detected between the two formulations of cephalexin. These results suggest that 24 h dose intervals would be appropriate with only one of the formulations and that the recommended dose rates for each product may need to be reviewed.

Norfloxacin nicotinate pharmacokinetics in unweaned and weaned calves

The pharmacokinetics of norfloxacin nicotinate were investigated in unweaned and weaned calves. Following intravenous administration of 7.5 and 15 mg/kg (calculated as norfloxacin base) the clearance values were 8.5 +/- 2.0 or 7.7 +/- 1.2 mL/min.kg (unweaned calves) and 11.7 +/- 3.2 or 16.1 +/- 3.3 mL/min.kg (weaned calves). Norfloxacin mean residence time and volume of distribution values were 211 +/- 33 or 227 +/- 41 min (unweaned calves) and 185 +/- 79 or 128 +/- 18 minutes (weaned calves), and 1.8 +/- 0.3 or 1.7 +/- 0.1 L/kg (unweaned calves) and 2.0 +/- 0.7 or 2.1 +/- 0.7 L/kg (weaned calves) following administration of the lower and higher dose, respectively. These results indicated that norfloxacin pharmacokinetics were similar at a dose range of 7.5-15 mg/kg. However, a significant difference was observed in clearance, mean residence time and the half-life values between the unweaned and weaned calves. The only major pharmacokinetic parameter which did not show a significant difference between the investigated groups was the volume of distribution. The pharmacokinetic differences between the non-ruminating (unweaned) and ruminating (weaned) animals seemed to result from changes in drug clearance. The absorption rate after intramuscular administration appeared to change as a result of dose increase. Norfloxacin bioavailability following intramuscular administration ranged from 73 to 106%. The results suggested that larger injection volumes may reduce the extent of absorption.

Clinical pharmacology of cefixime in unweaned calves

Cefixime is a unique third-generation oral cephalosporin. Its in vitro activity and pharmacokinetic properties have been studied to assess its potential for use in the therapy of newborn calf infections due to gram-negative bacteria. The minimum inhibitory concentrations of cefixime for 90% (MIC90) of field isolates of Escherichia coli, Salmonella and Pasteurella were 0.10-0.40 micrograms/mL. The serum disposition kinetics of cefixime following intravenous and oral administration was evaluated. The elimination half-life of cefixime after intravenous and oral administration was 3.5-4.0 h, the steady-state volume of distribution was 0.34 L/kg and approximately 90% of the drug was bound to serum proteins. Oral absorption was comparatively slow and bioavailability values for single 5 mg/kg doses were 20.2% after the administration of 200 mg of cefixime in capsules, 28.3% after dosing an aqueous solution of cefixime and 35.7% after fasted calves received the solution of cefixime. Mean serum drug concentrations 12 h after the cefixime solution was administered orally (5 mg/kg) were 1.05 micrograms/mL for the milk-fed calves and 1.76 micrograms/mL for the fasted calves. Computations showed that mean free drug concentrations equal to the MIC50 of the drug for gram-negative pathogens associated with newborn calf infections can be maintained in tissues by multiple treatments at 5 mg/kg every 12 h or 10 mg/kg every 24 h.

The effects on the pharmacokinetics of intravenous ceftiofur sodium in dairy cattle of simultaneous intravenous acetyl salicylate (aspirin) or probenecid

Ceftiofur sodium is a third-generation cephalosporin antibiotic. It is possible that non-steroidal anti-inflammatory drugs such as acetyl salicylate (aspirin) may be used concomitantly with ceftiofur sodium in dairy cattle. Therefore this study evaluated potential pharmacokinetic interactions between ceftiofur sodium and aspirin. In addition, this study evaluated the potential for interaction between ceftiofur and its active metabolites and the organic anion transporter. The organic anion transporter substrate used in this evaluation was probenecid. Ten healthy, non-pregnant, non-lactating dairy cows were used in a randomized complete three-way crossover design. In repeated experiments all cows were administered: (1) 2 mg of ceftiofur sodium per kg body weight by intravenous bolus or (2) 10 mg of probenecid per kg body weight by intravenous bolus, followed immediately by 2 mg of ceftiofur sodium per kg body weight by intravenous bolus or (3) 26 mg of aspirin per kg body weight by intravenous bolus, followed immediately by 2 mg of ceftiofur sodium per kg body weight by intravenous bolus. For treatment with ceftiofur sodium alone, the mean volume of distribution at steady-state Vd(ss) was 0.2 +/- 0.06 L/kg, the mean volume of distribution by the area method Vd(area) was 0.38 +/- 0.22 L/kg, mean residence time (MRT) was 6.5 +/- 1.8 h, mean residence time in peripheral tissues (MRTp) was 2.6 +/- 1.0 h, total body clearance (Cl) was 0.032 +/- 0.013 L/kg/h and elimination rate constant (beta) was 0.097 +/- 0.044 h-1 (mean +/- standard deviation). No statistically significant changes were detected as a result of preceding treatment with aspirin.(ABSTRACT TRUNCATED AT 250 WORDS)

Probenecid effect on cefuroxime pharmacokinetics in calves

Cefuroxime pharmacokinetics were studied in unweaned calves. The antibiotic was administered at 10 mg/kg to six calves i.v., to 12 calves i.m. and to ten of the previous 12 calves i.m. at 10 mg/kg together with probenecid at 40 mg/kg. Intramuscular doses of cefuroxime alone at 20 mg/kg were given to seven calves; to five of these calves cefuroxime was also given together with probenecid at 40 mg/kg and at 80 mg/kg. The serum concentration-time data were analyzed using statistical moment theory (SMT). The elimination half-life (t1/2) was 69.2 min (harmonic mean) after i.v. and 64.8 min and 64.9 min following i.m. administration of the lower and higher dose, respectively. Co-administration of probenecid did not affect the t1/2. The mean residence time (MRT) was 80.9 +/- 23.5 min (mean +/- SD) after i.v. and 117.8 +/- 9.3 min and 117.7 +/- 5.4 min after i.m. administration of cefuroxime at 10 and 20 mg/kg, respectively. The MRTi.m. following administration of cefuroxime at 10 mg/kg together with probenecid at 40 mg/kg was 140.0 +/- 8.8 min. The MRTi.m. values were 132.8 +/- 2.3 min and 150.8 +/- 5.1 min after cefuroxime was given at 20 mg/kg together with probenecid at 40 mg/kg or 80 mg/kg, respectively. The total body clearance (ClT) was 3.56 +/- 1.11 ml/min/kg and the volume of distribution at steady state (Vd(ss] 0.270 +/- 0.051 l/kg. The MIC90 values of cefuroxime were 16 micrograms/ml for E. coli and Salmonella isolates, 0.5 microgram/ml for Pasteurella multocida and 2.0 micrograms/ml for P. haemolytica.