Pharmacokinetics of danofloxacin in horses after intravenous, intramuscular and intragastric administration

Concentration-resistance relationship and PK/PD evaluation of danofloxacin against emergence of resistant Pasteurella multocida in an in vitro dynamic model

AIMS

This study aimed to assess the pharmacokinetic/pharmacodynamic (PK/PD) targets of danofloxacin to minimize the risk of selecting resistant Pasteurella multocida mutants and to identify the mechanisms underlying their resistance in an in vitro dynamic model, attaining the optimum dosing regimen of danofloxacin to improve its clinical efficacy based on the mutant selection window (MSW) hypothesis.

METHODS AND RESULTS

Danofloxacin at seven dosing regimens and 5 days of treatment were simulated to quantify the bactericidal kinetics and enrichment of resistant mutants upon continuous antibiotic exposure. The magnitudes of PK/PD targets associated with different efficacies were determined in the model. The 24 h area under the concentration-time curve (AUC) to minimum inhibitory concentration (MIC) ratios (AUC24h/MIC) of danofloxacin associated with bacteriostatic, bactericidal and eradication effects against P. multocida were 34, 52, and 64 h. This translates to average danofloxacin concentrations (Cav) over 24 h being 1.42, 2.17, and 2.67 times the MIC, respectively. An AUC/MIC-dependent antibacterial efficacy and AUC/mutant prevention concentration (MPC)-dependent enrichment of P. multocida mutants in which maximum losses in danofloxacin susceptibility occurred at a simulated AUC24h/MIC ratio of 72 h (i.e. Cav of three times the MIC). The overexpression of efflux pumps (acrAB-tolC) and their regulatory genes (marA, soxS, and ramA) was associated with reduced susceptibility in danofloxacin-exposed P. multocida. The AUC24h/MPC ratio of 19 h (i.e. Cav of 0.8 times the MPC) was determined to be the minimum mutant prevention target value for the selection of resistant P. multocida mutants.

CONCLUSIONS

The emergence of P. multocida resistance to danofloxacin exhibited a concentration-dependent pattern and was consistent with the MSW hypothesis. The current clinical dosing regimen of danofloxacin (2.5 mg kg-1) may have a risk of treatment failure due to inducible fluoroquinolone resistance.

Pharmacokinetics of danofloxacin in freshwater crocodiles (Crocodylus siamensis) after intramuscular injection

The present study evaluated the pharmacokinetic profiles of danofloxacin (DNX) in freshwater crocodiles (Crocodylus siamensis), following single intramuscular (i.m.) administrations at two different dosages of 6 and 12 mg/kg body weight (b.w.). Blood samples were collected at assigned times up to 168 h. DNX in the harvested crocodile plasma was extracted using liquid-liquid extraction and analyzed using a validated high-performance liquid chromatography method equipped with fluorescence detection. The pharmacokinetic analysis was performed using a non-compartmental approach. DNX in plasma was quantifiable from 5 min to 168 h after i.m. administration at the two dosages in freshwater crocodiles. The area under the curve (AUC) and maximum concentration (C_max ) values increased in a dose-dependent fashion. Long elimination half-life (48.18 and 67.29 h) and low clearance (0.024 and 0.020 ml/g h) were obtained in the high- and low-dose groups, respectively. According to the pharmacokinetic-pharmacodynamic surrogate (AUC_0-24h /MIC > 125), i.m. single administration of DNX at a dosage of 6 mg/kg b.w. is predicted to have antibacterial success for disease caused by bacteria with MIC < 0.04 μg/ml in the freshwater crocodile, C. siamensis.

Pharmacokinetic characteristics of danofloxacin in green sea (Chelonia mydas) and hawksbill sea (Eretmochelys imbricata) turtles

To date, the number of green sea and hawksbill sea turtles is in decline due to environmental, anthropogenic, and pathological factors. The present study described the pharmacokinetic characteristics of danofloxacin (DNX) in green sea and hawksbill sea turtles, following single intravenous (i.v.) and intramuscular (i.m.) administrations at single dosages of 6 mg/kg body weight (b.w.). Blood samples were collected at assigned times up to 168 h. DNX in the harvested plasma was cleaned up using liquid-liquid extraction and analyzed using a validated high-performance liquid chromatography method with fluorescence detection. The pharmacokinetic analysis was performed using a non-compartmental approach. DNX was quantifiable from 5 min to 168 h after i.v. and i.m. administrations at an identical dosage in both turtle types. No statistical differences were found in the pharmacokinetic parameters between green sea and hawksbill sea turtles. The long elimination half-life value of DNX obtained in green sea (35 h) and hawksbill sea (30.21 h) turtles was consistent with the quite large volume of distribution and the slow clearance rate. The high values of absolute bioavailability (87%-94%) should be advantageous for clinical use of DNX in sea turtles. According to the pharmacokinetic-pharmacodynamic surrogate (AUC_0-24 /MIC > 125), DNX is predicted to have antibacterial success for disease caused by bacteria with MIC < 0.04 µg/ml.

Population pharmacokinetics for danofloxacin in the intestinal contents of healthy and infected chickens

Avian pathogenic Escherichia coli could cause localized and systemic infection in the poultry, and danofloxacin is usually used to treat avian colibacillosis through oral administration. To promote prudent use of danofloxacin and reduce the emergence of drug-resistant E. coli strains, it is necessary to understand the population pharmacokinetics (PopPK) of danofloxacin in chicken intestines. In this study, reversed-phase high performance liquid chromatography (HPLC) with fluorescence detection was used to detect the concentrations of danofloxacin in the contents of duodenum, jejunum, and ileum of the healthy and infected chickens after single oral administration (5 mg/kg body weight). Then, the PopPK of danofloxacin in intestines were analyzed using NONMEM software. As a result, a two-compartment PK model best described the time-concentration profile of duodenal, jejunal, and ileal contents. Interestingly, absorption rate (K_a ), distribution volume (V), and clearance (CL) for danofloxacin from duodenal, jejunal to ileal contents were sequentially decreased in the healthy chickens. However, the trend of K_a , V, and CL of danofloxacin was changed dramatically in the intestine of infected chickens. K_a and V of danofloxacin in the jejunum were higher than in the ileum and duodenum. Compared with healthy chickens, K_a and V of danofloxacin in the duodenum decreased significantly, while increased in jejunum, respectively. It has been noted that K_a decreased and V increased in the ileum of infected chickens. Besides, CL in the duodenum, jejunum, and ileum of infected chickens was, respectively, lower than those of healthy chickens. Interestingly, the relative bioavailability (F) of danofloxacin in the ileum was relatively higher in both healthy and infected chickens. In addition, F in the duodenal, jejunal, and ileal contents of infected chickens was respectively higher than healthy chickens. In summary, the PopPK for danofloxacin in infected chicken intestines was quite different from healthy chickens. The absorption, distribution, and clearance of danofloxacin in healthy chickens decreased from duodenum to jejunum and to ileum. Moreover, the pharmacokinetic characteristics in the intestine of infected chickens changed significantly, and the pharmacokinetic characteristics in the ileum can be used as a representative of all intestinal segments.

Pharmacokinetic-pharmacodynamic integration of orbifloxacin in rabbits after intravenous, subcutaneous and intramuscular administration

The single-dose disposition kinetics of orbifloxacin were determined in clinically normal rabbits (n=6) after intravenous (i.v.), subcutaneous (s.c.) and intramuscular (i.m.) administration of 5 mg/kg bodyweight. Orbifloxacin concentrations were determined by high performance liquid chromatography with fluorescence detection. Minimal inhibitory concentrations (MICs) assay of orbifloxacin against 30 strains of Staphylococcus aureus from several European countries was performed in order to compute pharmacodynamic surrogate markers. The concentration-time data were analysed by compartmental and noncompartmental kinetic methods. Steady-state volume of distribution (V(ss)) and total body clearance (Cl) of orbifloxacin after i.v. administration were estimated to be 1.71+/-0.38 L/kg and 0.91+/-0.20 L/h x kg, respectively. Following s.c. and i.m. administration orbifloxacin achieved maximum plasma concentrations of 2.95+/-0.82 and 3.24+/-1.33 mg/L at 0.67+/-0.20 and 0.65+/-0.12 h, respectively. The absolute bio-availabilities after s.c. and i.m. routes were 110.67+/-11.02% and 109.87+/-8.36%, respectively. Orbifloxacin showed a favourable pharmacokinetic profile in rabbits. However, on account of the low AUC/MIC and C(max)/MIC indices obtained, its use by i.m. and s.c. routes against the S. aureus strains assayed in this study cannot be recommended given the risk of selection of resistant populations.

Pharmacokinetics and Milk Penetration of Orbifloxacin After Intravenous, Subcutaneous, and Intramuscular Administration to Lactating Goats

The single-dose disposition kinetics of orbifloxacin were determined in clinically normal lactating goats (n = 6) after intravenous, subcutaneous, and intramuscular administration of 2.5 mg of orbifloxacin/kg of body weight. Orbifloxacin concentrations were determined by HPLC with fluorescence detection. The concentration-time data were analyzed by compartmental and noncompartmental kinetic methods. Steady-state volume of distribution and clearance of orbifloxacin after intravenous administration were 1.13 +/- 0.08 L/kg and 0.40 +/- 0.11 L/h x kg, respectively. Following subcutaneous and intramuscular administration, orbifloxacin achieved maximum plasma concentrations of 1.85 +/- 0.20 and 1.66 +/- 0.14 mg/L at 1.25 +/- 0.22 and 0.87 +/- 0.38 h, respectively. The absolute bioavailabilities after subcutaneous and intramuscular routes were 108.96 +/- 17.61% and 105.01 +/- 15.61%, respectively. Orbifloxacin penetration from the blood into the milk was rapid and showed high levels of concentrations in milk secretion. From this data, orbifloxacin could have success against susceptible mastitis pathogens in goats.

Danofloxacin-mesylate is a substrate for ATP-dependent efflux transporters

BACKGROUND AND PURPOSE

Next to its broad antimicrobial spectrum, the therapeutic advantages of the fluoroquinolone antimicrobial drug Danofloxacin-Mesylate (DM) are attributed to its rapid distribution to the major target tissues such as lungs, intestines and the mammary gland in animals. Previous analyses revealed that effective drug concentrations are achieved also in luminal compartments of these organs, suggesting that active transport proteins facilitate excretion into the luminal space. Members of the ATP-Binding Cassette (ABC) superfamily, including P-gp, BCRP and MRP2 are known to be expressed in many tissue barriers and in cell-membranes facing luminal compartments. Hence we hypothesized that DM is a substrate for one of these efflux-transporters.

EXPERIMENTAL APPROACH

Confluent monolayers of Caco-2 cells, grown on microporous membranes in two-chamber devices were used. DM concentrations were measured by fluorimetric assay after HPLC of the culture media.

KEY RESULTS

DM transport across Caco-2 cells was asymmetric, with a rate of secretion exceeding that of absorption. The P-gp inhibitors PSC833 and GF120918 and the MRP-inhibitor MK571 partially decreased the secretion of DM and increased its absorption rate. The BCRP inhibitor, Ko143, decreased secretion only at a concentration of 1 microM. When DM was applied together with ciprofloxacin, secretion as well as absorption of DM decreased.

CONCLUSIONS AND IMPLICATIONS

DM is a substrate for the efflux transporters P-gp and MRP2, whereas the specific role of BCRP in DM transport needs further evaluation. These findings provide a mechanistic basis for the understanding of the pharmacokinetics of DM in healthy and diseased individuals.