Comparative mutant prevention concentration and mechanism of resistance to veterinary fluoroquinolones in Staphylococcus pseudintermedius

Background – The problem of antibacterial drug resistance is increasing worldwide, in part due to the therapeutic concentrations currently used based on the minimal inhibitory concentration (MIC) as a measure of potency are often the very concentrations required to selectively enrich the resistant mutant portion of the population. A mutant prevention concentration (MPC)‐based dosing strategy is suggested to improve the therapeutic outcome based on the MIC. Objective – Our aim was to investigate the MPC and mechanism of resistance to various fluoroquinolones using recent Staphylococcus pseudintermedius isolates from canine pyoderma. Methods – The broth microdilution method for MIC and a series of agar plates containing different concentrations of fluoroquinolones were inoculated with ～10¹⁰ colony‐forming units of the bacterial culture for MPC were used. PCR was used to identify mutation in the resistant isolates. Results – The rank order of potency based on MIC and MPC was ciprofloxacin = enrofloxacin ≥ marbofloxacin > difloxacin ≥ orbifloxacin. Integrating our data with reported pharmacokinetic data at the recommended dose ranges revealed that only high doses of ciprofloxacin, enrofloxacin and marbofloxacin could achieve a maximal plasma concentration (C_max) greater than the MPC of 90% of isolates (C_max/MPC₉₀). The overall rank of potency against S. pseudintermedius, based on C_max/MIC, C_max/MPC, the area under concentration–time curve (AUC)/MIC and AUC/MPC values, was in decreasing order: enrofloxacin > ciprofloxacin ≥ marbofloxacin ≥ orbifloxacin = difloxacin. Sequencing of the quinolone resistant determining region of gyrA, gyrB, grlA and grlB of resistant strains showed a base‐pair substitution in both gyrA and gyrB that resulted in Ser‐84 to Leu and Ser‐80 to Arg amino acid changes, respectively. Conclusions and clinical importance – High doses of ciprofloxacin, enrofloxacin and marbofloxacin could minimize the selection of resistant mutants, whereas the possibility of selecting mutants with the conventional doses of difloxacin and orbifloxacin, and low clinical doses of all fluoroquinolones, seems high.     

Pharmacokinetic and pharmacodynamic testing of marbofloxacin administered as a single injection for the treatment of bovine respiratory disease

Vallé, M., Schneider, M., Galland, D., Giboin, H., Woehrlé, F. Pharmacokinetic and pharmacodynamic testing of marbofloxacin administered as a single injection for the treatment of bovine respiratory disease. J. vet. Pharmacol. Therap. 35, 519–528. New approaches in Pharmacokinetic/Pharmacodynamic (PK/PD) integration suggested that marbofloxacin, a fluoroquinolone already licensed for the treatment of bovine respiratory disease at a daily dosage of 2 mg/kg for 3–5 days, would be equally clinically effective at 10 mg/kg once (Forcyl^®), whilst also reducing the risk of resistance. This marbofloxacin dosage regimen was studied using mutant prevention concentration (MPC), PK simulation, PK/PD integration and an in vitro dynamic system. This system simulated the concentration–time profile of marbofloxacin in bovine plasma established in vivo after a single 10 mg/kg intramuscular dose and killing curves of field isolated Pasteurellaceae strains of high (minimum inhibitory concentration (MIC) MIC ≤0.03 μg/mL), average (MIC of 0.12–0.25 μg/mL) and low (MIC of 1 μg/mL) susceptibility to marbofloxacin. The marbofloxacin MPC values were 2‐ to 4‐fold the MIC values for all Mannheimia haemolytica, Pasteurella multocida tested. Marbofloxacin demonstrated a concentration‐dependant killing profile with bactericidal activity observed within 1 h for most strains. No resistance development (MIC ≥4 μg/mL) was detected in the dynamic tests. Target values for risk of resistance PK/PD surrogates (area under the curve (AUC) AUC_{24 h}/MPC and T_>MPC/T_MSW ratio) were achieved for all clinically susceptible pathogens. The new proposed dosing regimen was validated in vitro and by PK/PD integration confirming the single‐injection short‐acting antibiotic concept.     

In vivo activity of cefquinome against Riemerella anatipestifer using the pericarditis model in the duck

Cefquinome is a fourth‐generation cephalosporin with broad‐spectrum antibacterial activity, including activity against enteric gram‐negative bacilli such as Riemerella anatipestifer. The pericarditis model was used to examine the pharmacodynamic characteristics of cefquinome against R. anatipestifer. Serum levels of cefquinome following the administration of different doses were determined by LC‐MS/MS. Ducks with ca. 10⁶ CFU/mL at the initiation of therapy were treated with cefquinome at doses that ranged from 0.0156 to 2 mg/kg of body weight/day (in 3, 6, 12, or 24 divided doses) for 24 h. The percentage of a 24‐h dosing interval that the unbound serum cefquinome concentrations exceeded the MIC (fT > MIC) were the pharmacokinetic (PK)–pharmacodynamic (PD) parameter that best correlated with efficacy (R² 86.3% for R. anatipestifer, compared with 58.9% for the area under the concentration–time curve/MIC and 10.6% for peak/MIC). A sigmoid E_max model was used to estimate the magnitudes of the %fT > MIC associated with net bacterial stasis, a 1‐log₁₀ CFU reduction from baseline, and a 2‐log₁₀ CFU reduction from baseline; the corresponding values were (22.5 ± 1.3) %, (35.2 ± 4.5) %, and (42.4 ± 2.7) %. These data showed that treatment with cefquinome results in marked antibacterial effects in qvivo against R. anatipestifer and that the host's immunity may also play a key role in the anti‐infective therapy process.     

Effect of supportive therapy on the pharmacokinetics of intravenous marbofloxacin in endotoxemic sheep

The purpose of this study was to determine the influences of supportive therapy (ST) on the pharmacokinetics (PK) of marbofloxacin in lipopolysaccharide (LPS)-induced endotoxemic sheep. Furthermore, minimum inhibitory concentration (MIC) of marbofloxacin against Escherichia coli, Mannheimia haemolytica, Pasteurella multocida, Klebsiella pneumoniae, Salmonella spp., and Staphylococcus aureus was determined. The study was performed using a three-period cross PK design following a 15-day washout period. In the first period, marbofloxacin (10 mg/kg) was administered by an intravenous (IV) injection. In the second and third periods, marbofloxacin was co-administered with ST (lactated ringer + 5% dextrose + 0.45% sodium chloride, IV, 20 ml/kg, dexamethasone 0.5 mg/kg, SC) and ST + LPS (E. coli O55:B5, 10 µg/kg), respectively. Plasma marbofloxacin concentration was measured using HPLC-UV. Following IV administration of marbofloxacin alone, the , AUC_0–∞, Cl_T, and V_dss were 2.87 hr, 34.73 hr × µg/ml, 0.29 L hr⁻¹ kg⁻¹, and 0.87 L/kg, respectively. While no change was found in the MBX + ST group in terms of the PK parameters of marbofloxacin, it was determined that the Cl_T of marbofloxacin decreased, AUC_0–∞ increased, and and MRT prolonged in the MBX + ST + LPS group. MIC values of marbofloxacin were 0.031 to >16 µg/ml for E. coli, 0.016 to >16 µg/ml for M. haemolytica, 0.016–1 µg/ml for P. multocida, 0.016–0.25 µg/ml for K. pneumoniae, 0.031–0.063 µg/ml for Salmonella spp., and 0.031–1 µg/ml for S. aureus. The study results show the necessity to make a dose adjustment of marbofloxacin following concomitant administration of ST in endotoxemic sheep. Also, the PK and pharmacodynamic effect of marbofloxacin needs to be determined in naturally infected septicemic sheep following concomitant administration of single and ST.     

Absorption of enrofloxacin and marbofloxacin after oral and subcutaneous administration in diseased koalas (Phascolarctos cinereus)

Griffith, J.E., Higgins, D.P., Li, K.M., Krockenberger, M.B., Govendir, M. Absorption of enrofloxacin and marbofloxacin after oral and subcutaneous administration in diseased koalas (Phascolarctos cinereus). J. vet. Pharmacol. Therap. 33 , 595–604. Koalas (n = 43) were treated daily for up to 8 weeks with enrofloxacin: 10 mg/kg subcutaneously (s.c.), 5 mg/kg s.c., or 20 mg/kg per os (p.o.); or marbofloxacin: 1.0–3.3 mg/kg p.o., 10 mg/kg p.o. or 5 mg/kg s.c. Serial plasma drug concentrations were determined on day 1 and again at approximately 2 weeks, by liquid chromatography. The median (range) plasma maximum concentrations (C_max) for enrofloxacin 5 mg/kg s.c. and 10 mg/kg s.c. were 0.83 (0.68–1.52) and 2.08 (1.34–2.96) μg/mL and the median (range) T_max were 1.5 h (1–2) and 1 h (1–2) respectively. Plasma concentrations of orally dosed marbofloxacin were too low to be quantified. Oral administration of enrofloxacin suggested absorption rate limited disposition pharmacokinetics; the median (range) C_max for enrofloxacin 20 mg/kg p.o. was 0.94 (0.76–1.0) μg/mL and the median (range) T_max was 4 h (2–8). Oral absorption of both drugs was poor. Plasma protein binding for enrofloxacin was 55.4 ± 1.9% and marbofloxacin 49.5 ± 5.3%. Elevations in creatinine kinase activity were associated with drug injections. Enrofloxacin and marbofloxacin administered at these dosage and routes are unlikely to inhibit the growth of chlamydial pathogens in vivo.     

In vitro antimicrobial activity of a commercial ear antiseptic containing chlorhexidine and Tris–EDTA

Minimum bactericidal concentrations (MBCs) of a commercial ear antiseptic containing chlorhexidine 0.15% and Tris–EDTA (Otodine^®) were determined by broth microdilution for 150 isolates representing the most common pathogens associated with canine otitis. The microorganisms were classified into three groups according to their levels of susceptibility. The most susceptible group included Staphylococcus pseudintermedius, Malassezia pachydermatis, Streptococcus canis and Corynebacterium auriscanis, which were generally killed by 1 : 64 dilution of the antiseptic product (MBC = 23/0.8 μg/mL of chlorhexidine/Tris–EDTA). The most resistant organism was Proteus mirabilis, which survived up to 1 : 8 dilution of the product (MBC = 375/12 μg/mL). Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus displayed intermediate MBCs ranging between 188/6 and 47/1.5 μg/mL. Interestingly, S. pseudintermedius was more susceptible than S. aureus, and no significant difference was observed between meticillin‐resistant and meticillin‐susceptible isolates within each species, indicating that antiseptic use is unlikely to co‐select for meticillin resistance. Although the concentrations required for killing (MBCs) varied considerably with microorganism type, the combination of chlorhexidine 0.15% and Tris–EDTA was active against all the pathogens most commonly involved in canine otitis.     

Pharmacokinetics of marbofloxacin in pigs after intravenous and intramuscular administration of a single dose of 8 mg/kg: dose proportionality,influence of the age of the animals and urinary elimination

The pharmacokinetics of marbofloxacin in pigs were evaluated as a function of dose and animal age following intravenous and intramuscular administration of a 16% solution (Forcyl^®). The absolute bioavailability of marbofloxacin as well as the dose proportionality was evaluated in 27‐week‐old fattening pigs. Blood PK and urinary excretion of marbofloxacin were evaluated after a single intramuscular dose of 8 mg/kg in 16‐week‐old male pigs. An additional group of 12‐week‐old weaned piglets was used for the evaluation of age‐related kinetics. The plasma and urine concentration of marbofloxacin was determined using a HPLC method. Pharmacokinetic parameters were calculated using noncompartmental methods. After intravenous administration in 27‐week‐old fattening pigs, the total body clearance was 0.065 L/h·kg. After intramuscular administration to the same animals, the mean observed C_max was 6.30 μg/mL, and the AUC_INF was 115 μg·h/mL. The absolute bioavailability was 91.5%, and dose proportionality was shown within the dose range of 4–16 mg/kg. The renal clearance was about half of the value of the total clearance. The total systemic clearance values significantly decreased as a function of age, being 0.092 L/h·kg and 0.079 L/h·kg in pigs aged 12 and 16 weeks, respectively.     

Pharmacokinetic-pharmacodynamic integration of orbifloxacin in Japanese quail (Coturnix japonica) following oral and intravenous administration

Hawkins, M. G., Taylor, I. T., Byrne, B. A., Armstrong, R. D., Tell, L. A. Pharmacokinetic–pharmacodynamic integration of orbifloxacin in Japanese quail (Coturnix japonica) following oral and intravenous administration. J. vet. Pharmacol. Therap. 34 , 350–358. The pharmacokinetics of single‐dose administration of orbifloxacin were determined in Japanese quail (Coturnix japonica) at dosages of 5 mg/kg intravenous (i.v. n = 12) and 7.5 mg/kg oral (p.o.; n = 5), 10 mg/kg p.o. (n = 5), 15 mg/kg p.o. (n = 12) and 20 mg/kg p.o. (n = 5) via HPLC. Orbifloxacin minimal inhibitory concentrations (MICs) against 22 microbial isolates from various bird species were performed to calculate pharmacodynamic surrogate markers. The concentration–time data were analyzed using a naïve pooled data (NPD) approach and compartmental and noncompartmental methods. Steady‐state volume of distribution (Vd_ss) and total body clearance (Cl) after i.v. administration were estimated to be 1.27 L/kg and 0.60 L/h·kg, respectively. Following 15 and 20 mg/kg p.o. dose, bioavailability was 102% and 117%, respectively. The harmonic mean of the corresponding terminal half‐lives (T_1/2λ_z) across all the dose groups was 1.71 h. The C_max/MIC₉₀ and AUC_0∞24/MIC₉₀ for the 15 and 20 mg/kg p.o. doses were ≥5.22 and ≥8.98, and ≥25.80 and ≥39.37 h, respectively. The results of this study suggest that 20 mg/kg orbifloxacin p.o. would be a rational daily dose to treat susceptible infections in Japanese quail not intended for food consumption. For more sensitive bacterial organisms, 15 mg/kg p.o. may also be effective.     

The pharmacokinetics of mavacoxib,a long‐acting COX‐2 inhibitor,in young adult laboratory dogs

Cox, S.R., Lesman, S.P., Boucher, J.F., Krautmann, M.J., Hummel, B.D., Savides, M., Marsh, S., Fielder, A., Stegemann, M.R. The pharmacokinetics of mavacoxib, a long‐acting COX‐2 inhibitor, in young adult laboratory dogs. J. vet. Pharmacol. Therap. 33 , 461–470. The pharmacokinetics of mavacoxib were evaluated in an absolute bioavailability study, a dose‐proportionality study and a multi‐dose study in young healthy adult laboratory Beagle dogs and in a multi‐dose safety study in Beagle‐sized laboratory Mongrel dogs. When administered as the commercial tablet formulation at 4 mg/kg body weight (bw) to fasted dogs, the absolute bioavailability (F) of mavacoxib was 46.1%; F increased to 87.4% when mavacoxib was administered with food. Following intravenous administration, the total body plasma clearance of mavacoxib was 2.7 mL·h/kg, and the apparent volume of distribution at steady‐state was 1.6 L/kg. The plasma protein binding of mavacoxib was approximately 98% in various in vitro and ex vivo studies. The dose‐normalized area under the plasma concentration–time curve was similar in Beagle and Beagle‐sized Mongrel dogs when mavacoxib was administered with food. Mavacoxib exhibited dose‐proportional pharmacokinetics for single oral doses of 2–12 mg/kg in Beagle dogs and for multiple oral doses of 5–25 mg/kg in Beagle‐sized Mongrel dogs. Only minor accumulation occurred when mavacoxib was administered at doses of 2–25 mg/kg bw orally to laboratory dogs with a 2‐week interval between the 1st two doses but with a monthly interval thereafter. Across all three Beagle studies (n = 63) the median terminal elimination half‐life (t_½) was 16.6 days, with individual values ranging 7.9–38.8 days. The prolonged t_½ for mavacoxib supports the approved regimen in which doses are separated by 2–4 weeks.     

Biofilm production by pathogens associated with canine otitis externa,and the antibiofilm activity of ionophores and antimicrobial adjuvants

Otitis externa (OE) is a frequently reported disorder in dogs associated with secondary infections by Staphylococcus, Pseudomonas and yeast pathogens. The presence of biofilms may play an important role in the resistance of otic pathogens to antimicrobial agents. Biofilm production of twenty Staphylococcus pseudintermedius and twenty Pseudomonas aeruginosa canine otic isolates was determined quantitatively using a microtiter plate assay, and each isolate was classified as a strong, moderate, weak or nonbiofilm producer. Minimum biofilm eradication concentration (MBEC) of two ionophores (narasin and monensin) and three adjuvants (N‐acetylcysteine (NAC), Tris‐EDTA and disodium EDTA) were investigated spectrophotometrically (OD_570nm) and quantitatively (CFU/ml) against selected Staphylococcus and Pseudomonas biofilm cultures. Concurrently, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of planktonic cultures were assessed. 16/20 of the S. pseudintermedius clinical isolates were weak biofilm producers. 19/20 P. aeruginosa clinical isolates produced biofilms and were distributed almost equally as weak, moderate and strong biofilm producers. While significant antibiofilm activity was observed, no MBEC was achieved with narasin or monensin. The MBEC for NAC ranged from 5,000–10,000 µg/ml and from 20,000–80,000 µg/ml against S. pseudintermedius and P. aeruginosa, respectively. Tris‐EDTA eradicated P. aeruginosa biofilms at concentrations ranging from 6,000/1,900 to 12,000/3,800 µg/ml. The MBEC was up to 16‐fold and eightfold higher than the MIC/MBC of NAC and Tris‐EDTA, respectively. Disodium EDTA reduced biofilm growth of both strains at concentrations of 470 µg/ml and higher. It can be concluded that biofilm production is common in pathogens associated with canine OE. NAC and Tris‐EDTA are effective antibiofilm agents in vitro that could be considered for the treatment of biofilm‐associated OE in dogs.     

Activity of cefquinome against extended‐spectrum β‐lactamase‐producing Klebsiella pneumoniae in neutropenic mouse thigh model

Increasing prevalence of extended‐spectrum β‐lactamase (ESBL)‐producing Klebsiella pneumoniae (K. pneumoniae) is of clinical concern. The objective of our study was to examine the in vivo activity of cefquinome against ESBL‐producing K. pneumoniae strain using a neutropenic mouse thigh infection model. Cefquinome kinetics and protein binding in infected neutropenic mice were measured by liquid chromatography–tandem mass spectrometry (LC‐MS/MS). Dose‐fractionation studies over a 24‐h dose range of 2.5–320 mg/kg were administered every 3, 6, 12, or 24 h. The percentage of the dosing interval that the free‐drug serum levels exceed the MIC (%fT > MIC) was the PK–PD index that best correlated with cefquinome efficacy (R² = 86%). Using a sigmoid E_max model, the magnitudes of %fT > MIC producing net bacterial stasis, a 1‐log₁₀ kill and a 2‐log₁₀ kill over 24 h, were estimated to be 20.07%, 29.57%, and 55.12%, respectively. These studies suggest that optimal cefquinome PK/PD targets are not achieved in pigs, sheep, and cattle at current recommended doses (1?2 mg/kg). Further studies with higher doses in the target species are needed to ensure therapeutic concentration, if cefquinome is used for treatment of K. pneumoniae infection.     

Pharmacokinetics of ceftiofur crystalline-free acid sterile suspension in the equine

Collard, W. T., Cox, S. R., Lesman, S. P., Grover, G. S., Boucher, J. F., Hallberg, J. W., Robinson, J. A., Brown, S. A. Pharmacokinetics of ceftiofur crystalline‐free acid sterile suspension in the equine. J. vet. Pharmacol. Therap. 34 , 476–481. Absolute bioavailability and dose proportionality studies were performed with ceftiofur in horses. In the absolute bioavailability study, thirty animals received either an intravenous dose of ceftiofur sodium at 1.0 mg/kg or an intramuscular (i.m.) dose of ceftiofur crystalline‐free acid (CCFA) at 6.6 mg/kg. In the dose proportionality study, 48 animals received daily i.m. ceftiofur sodium injections at 1.0 mg/kg for ten doses or two doses of CCFA separated by 96 h, with CCFA doses of 3.3, 6.6, or 13.2 mg/kg. Noncompartmental and mixed‐effect modeling procedures were used to assess pharmacokinetics (PK). CCFA was well absorbed with a bioavailability of 100%. AUC_0–∞ and C_max increased in a dose‐related manner following administration of the two doses of CCFA at 3.3, 6.6, and 13.2 mg/kg. The least‐squares mean terminal half‐life (t_½) following the tenth daily i.m. injection of ceftiofur sodium at 2.2 mg/kg was 40.8 h, but the least‐squares mean t_½ following the second i.m. injection of CCFA at 6.6 mg/kg was 100 h. The time that plasma ceftiofur equivalent concentrations remain above a threshold concentration of 0.2 μg/mL has been associated with efficacy, and following administration of two 6.6 mg/kg doses of CCFA, the mean time above 0.2 μg/mL was 262 h. Simulations with the nonlinear mixed‐effect PK model predicted that more than 97.5% of horses will have plasma ceftiofur equivalent concentrations >0.2 μg/mL for 96 h after the second 6.6 mg/kg dose of CCFA.     

Analgesic and anti‐inflammatory actions of robenacoxib in acute joint inflammation in dog

Schmid, V. B., Spreng, D. E., Seewald, W., Jung, M., Lees, P., King, J. N. Analgesic and anti‐inflammatory actions of robenacoxib in acute joint inflammation in dog. J. vet. Pharmacol. Therap. 33 , 118–131. The objectives of this study were to establish dose–response and blood concentration–response relationships for robenacoxib, a novel nonsteroidal anti‐inflammatory drug with selectivity for inhibition of the cyclooxygenase (COX)‐2 isoenzyme, in a canine model of synovitis. Acute synovitis of the stifle joint was induced by intra‐articular injection of sodium urate crystals. Robenacoxib (0.25, 0.5, 1.0, 2.0 and 4.0 mg/kg), placebo and meloxicam (0.2 mg/kg) were administered subcutaneously (s.c.) 3 h after the urate crystals. Pharmacodynamic endpoints included data from forceplate analyses, clinical orthopaedic examinations and time course of inhibition of COX‐1 and COX‐2 in ex vivo whole blood assays. Blood was collected for pharmacokinetics. Robenacoxib produced dose‐related improvement in weight‐bearing, pain and swelling as assessed objectively by forceplate analysis (estimated ED₅₀ was 1.23 mg/kg for z peak force) and subjectively by clinical orthopaedic assessments. The analgesic and anti‐inflammatory effects of robenacoxib were significantly superior to placebo (0.25–4 mg/kg robenacoxib) and were non‐inferior to meloxicam (0.5–4 mg/kg robenacoxib). All dosages of robenacoxib produced significant dose‐related inhibition of COX‐2 (estimated ED₅₀ was 0.52 mg/kg) but no inhibition of COX‐1. At a dosage of 1–2 mg/kg administered s.c., robenacoxib should be at least as effective as 0.2 mg/kg of meloxicam in suppressing acute joint pain and inflammation in dogs.     

In vitro antiseptic susceptibilities for Staphylococcus pseudintermedius isolated from canine superficial pyoderma in Japan

Background –  Topical therapy, particularly with chlorhexidine, is becoming increasingly common as a treatment option for canine pyoderma; however, there are limited studies on the susceptibility of Staphylococcus pseudintermedius to chlorhexidine compounds. Objectives –  To determine the in vitro susceptibility of both meticillin‐resistant and meticillin‐susceptible S. pseudintermedius isolates to chlorhexidine and other antiseptic agents and the presence of multidrug efflux pump genes. Samples –  One hundred S. pseudintermedius isolates from 23 initial and 77 recurrent cases of canine pyoderma. Methods –  After bacterial identification and mecA testing, minimal inhibitory concentrations (MICs) of antiseptic agents were determined. Multidrug efflux pump genes, including qacA, qacB and smr, were identified. Results –  Of the 100 isolates, 57 were identified as meticillin‐resistant S. pseudintermedius. The MIC₉₀ of chlorhexidine acetate, chlorhexidine gluconate, acriflavine, ethidium bromide and benzalkonium chloride were 1, 1, 2, 0.5 and 2 μg/mL, respectively. Multidrug efflux pump genes qacA, qacB and smr were not detected in any of the isolates. Conclusions and clinical importance –  The MICs for chlorhexidine and other antiseptics remain low, and multidrug efflux pump genes were not found in the tested isolates.     

Evaluation of an extended‐release formulation of ceftiofur crystalline‐free acid in koi (Cyprinus carpio)

The use of an extended release ceftiofur crystalline‐free acid formulation (CCFA, Excede For Swine^®, Pfizer Animal Health) in koi was evaluated after administration of single intramuscular (i.m.) or intracoelomic (i.c.) doses. Twenty koi were divided randomly into a control group and four treatment groups (20 mg/kg i.m., 60 mg/kg i.m., 30 mg/kg i.c., and 60 mg/kg i.c.). Serum ceftiofur‐free acid equivalents (CFAE) concentrations were quantified. The pharmacokinetic data were analyzed using a nonlinear mixed‐effects approach. Following a CCFA injection of 60 mg/kg i.m., time durations that serum CFAE concentrations were above the target concentration of 4 μg/mL ranged from 0.4 to 2.5 weeks in 3 of 4 fish, while serum CFAE concentrations remained below 4 μg/mL for lower doses evaluated. Substantial inter‐individual variations and intra‐individual fluctuations of CFAE concentrations were observed for all treatment groups. Histological findings following euthanasia included aseptic granulomatous reactions, but no systemic adverse effects were detected. Given the unpredictable time vs. CFAE concentration profiles for treated koi, the authors would not recommend this product for therapeutic use in koi at this time. Further research would be necessary to correlate serum and tissue concentrations and to better establish MIC data for Aeromonas spp. isolated from naturally infected koi.     

Enrofloxacin‐based therapeutic strategy for the prevention of endometritis in susceptible mares

González, C., Moreno, L., Fumuso, E., García, J., Rivulgo, M., Confalonieri, A., Sparo, M., Sanchez Bruni, S. Enrofloxacin‐based therapeutic strategy for the prevention of endometritis in susceptible mares. J. vet. Pharmacol. Therap. 33 , 287–294. Enrofloxacin (EFX) is often used empirically to prevent uterine infections in mares in order to improve efficiency on Commercial Embryo Transfer Farms. This study investigated the uterine distribution of EFX and its metabolite ciprofloxacin (CFX) in mares and assessed the minimal inhibitory concentrations (MIC) of EFX against various common pathogens as a basis for establishing a rational dosing schedule. Plasma and uterine pharmacokinetic (PK) studies were performed in two groups (n = 5) of healthy mares following intravenous (i.v.) administration of EFX at either 2.5 and at 5 mg/kg bodyweight. Plasma and endometrial tissue samples, taken before for up to 48 h after treatment were analysed by Reverse Phase HPLC. MIC values for wild strains of Gram‐negative (Escherichia coli, Pseudomonas aeruginosa) and Gram‐positive bacteria (β‐haemolytic streptococci) ranged from 0.25–2 and 1.5–3.0 μg/mL respectively. In terms of tissue distribution, the sum of the endometrial concentrations of the parent drug (EFX) and its active metabolite (CFX) (in terms of AUC), exceeded those in plasma by 249% and 941% following administration of EFX at 2.5 and 5 mg/kg respectively. After i.v. treatment with EFX at 5 mg/kg, endometrial concentrations of EFX and CFX above the MIC value were detected for 36–48 and 22–43 h posttreatment for Gram‐negative and ‐positive isolates respectively. Concentrations above MIC were maintained for much shorter periods at the lower (2.5 mg/kg) treatment dose. Based on these results, a conventional dose (5 mg/kg) of EFX given prebreeding followed by two further doses at 36–48 h postbreeding are proposed as a rational strategy for using of EFX as a preventative therapy against a variety of common bacterial strains associated with equine endometritis.     

In vitro assessment of chloramphenicol and florfenicol as second‐line antimicrobial agents in dogs

The aim of this study was to evaluate the potential of chloramphenicol and florfenicol as second‐line antimicrobial agents for treatment of infections caused by methicillin‐resistant Staphyococcus pseudintermedius (MRSP) and extended‐spectrum β‐lactamase (ESBL)‐producing Escherichia coli in dogs, through a systematic in vitro assessment of the pharmacodynamic properties of the two drugs. Minimum inhibitory concentrations (MIC) and phenicol resistance genes were determined for 169 S. pseudintermedius and 167 E. coli isolates. Minimum bactericidal concentrations (MBC), time‐killing kinetics, and postantibiotic effect (PAE) of both agents against wild‐type isolates of each species were assessed. For S. pseudintermedius, the chloramphenicol MIC₉₀ was 32 μg/mL. No florfenicol resistance was detected in this species (MIC_90 = 4 μg/mL). The MIC₉₀ of both agents against E. coli was 8 μg/mL. Resistance genes found were cat_pC221 in S. pseudintermedius and catA1 and/or floR in E. coli. The phenicols displayed a time‐dependent, mainly, bacteriostatic effect on both species. Prolonged PAEs were observed for S. pseudintermedius, and no PAEs were detected for E. coli. More research into determination of PK/PD targets of efficacy is needed to further assess the clinical use of chloramphenicol and florfenicol as second‐line agents in dogs, optimize dosage regimens, and set up species‐specific clinical break points.     

Comparative Pharmacokinetics and bioavailability of marbofloxacin in geese (Anser Anser domesticus) after two sites of intramuscular administrations

The pharmacokinetics of marbofloxacin (MAR) was compared in geese (Anser Anser domesticus) after single intravenous (IV) and intramuscular (IM) (thigh and pectoral muscles) administrations of 5 mg/kg. Serum concentrations of MAR were determined with high-performance liquid chromatography (HPLC) method. Serum MAR concentrations versus time were analyzed by a noncompartmental method. After IV administration, MAR showed high volume of distribution at steady state (V_dss) of 5.24 ± 1.08 L/kg. The serum body clearance (Cl) and elimination half-life (T_1/2λz) of MAR were 0.79 ± 0.07 L hr⁻¹ kg⁻¹ and 6.94 ± 1.12 hr, respectively. The peak of MAR serum concentrations C_max achieved at one and 0.50 hr after thigh and pectoral IM sites of injections, respectively, were 1.20 and 0.91 μg/ml. Significant differences were found in the mean absorption time (MAT), the systemic bioavailability (F%), and elimination parameters of MAR between two sites of injections, indicating that the absorption was fairly slow and complete after thigh IM injection. The pharmacokinetics of MAR in geese diverged according to the site of IM injection following a parallel study design. We recommend the thigh muscle as IM site of injection to obtain maximum concentrations of the administered drug in geese.     

The pharmacokinetics of maropitant citrate dosed orally to dogs at 2 mg/kg and 8 mg/kg once daily for 14 days consecutive days

The pharmacokinetics of maropitant were evaluated in beagle dogs dosed orally with Cerenia^® tablets (Pfizer Animal Health) once daily for 14 consecutive days at either 2 mg/kg or 8 mg/kg bodyweight. Noncompartmental pharmacokinetic analysis was performed on the plasma concentration data to measure the AUC_0–24 (after first and last doses), C_t (trough concentration—measured 24 h after each dose), C_max (after first and last doses), t_max (after first and last doses), λ_z (terminal disposition rate constant; after last dose), t_1/2 (after last dose), and CL/F (oral clearance; after last dose). Maropitant accumulation in plasma was substantially greater after fourteen daily 8 mg/kg doses than after fourteen daily 2 mg/kg doses as reflected in the AUC_0–24 accumulation ratio of 4.81 at 8 mg/kg and 2.46 at 2 mg/kg. This is most likely due to previously identified nonlinear pharmacokinetics of maropitant in which high doses (8 mg/kg) saturate the metabolic clearance mechanisms and delay drug elimination. To determine the time to reach steady‐state maropitant plasma levels, a nonlinear model was fit to the least squares (LS) means maropitant C_t values for each treatment group. Based on this model, 90% of steady‐state was determined to occur at approximately four doses for daily 2 mg/kg oral dosing and eight doses for daily 8 mg/kg oral dosing.     

Pharmacokinetic/pharmacodynamic relationship of marbofloxacin against Aeromonas hydrophila in Chinese soft‐shelled turtles (Trionyx sinensis)

The single‐dose disposition kinetics of the antibiotic marbofloxacin were determined in Chinese soft‐shelled turtles (n = 10) after oral and intramuscular (i.m.) dose of 10 mg/kg bodyweight. The in vitro and ex vivo activities of marbofloxacin in serum against a pathogenic strain of Aeromonas hydrophila were determined. A concentration‐dependent antimicrobial activity of marbofloxacin was confirmed for levels lower than 4 × MIC. For in vivo PK data, values of AUC: minimum inhibitory concentration (MIC) ratio for serum were 1166.6 and 782.4 h, respectively, after i.m. and oral dosing of marbofloxacin against a pathogenic strain of A. hydrophila (MIC = 0.05 μg/mL). The ex vivo growth inhibition data after oral dosing were fitted to the inhibitory sigmoid Emax equation to provide the values of AUC/MIC required to produce bacteriostasis, bactericidal activity and elimination of bacteria. The respective values were 23.79, 36.35 and 126.46 h. It is proposed that these findings might be used with MIC₅₀ or MIC₉₀ data to provide a rational approach to the design of dosage schedules, which optimize efficacy in respect of bacteriological as well as clinical cures.