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

Can membrane permeability of zwitterionic compounds be predicted by the solubility-diffusion model?

Zwitterions contain both positively and negatively charged functional groups, resulting in an overall net neutral charge. Nevertheless, the membrane permeability of the zwitterionic form of a compound is assumed to be much lower than the permeability of the uncharged neutral form. Although a significant proportion of pharmaceuticals are zwitterionic, it has not been clear so far whether their permeability is dominated by the permeation of the zwitterionic or the neutral form, since neutral fractions are often quite low as compared to the zwitterionic fraction. This complicates the in silico prediction of the permeability of zwitterionic compounds. In this work, we re-evaluated existing in vitro permeability data from literature measured with Caco-2/MDCK cell assays, using more strict exclusion criteria for effects like diffusion limitation by the aqueous boundary layers, paracellular transport, active transport and retention. Using this re-evaluated data set, we show that extracted intrinsic permeabilities of the neutral fraction are well predicted by the solubility-diffusion model (RMSE = 1.21; n = 18) if the permeability of the zwitterionic species is assumed negligible. Our work thus suggests that only the neutral species is relevant for the membrane permeability of zwitterionic compounds, and that membrane permeability of zwitterionic compounds is indeed predictable by the solubility-diffusion model.

Pitfalls in evaluating permeability experiments with Caco-2/MDCK cell monolayers

When studying the transport of molecules across biological membranes, intrinsic membrane permeability (P0) is more informative than apparent permeability (Papp), because it eliminates external (setup-specific) factors, provides consistency across experiments and mechanistic insight. It is thus an important building block for modeling the total permeability in any given scenario. However, extracting P0 is often difficult, if not impossible, when the membrane is not the dominant transport resistance. In this work, we set out to analyze Papp values measured with Caco-2/MDCK cell monolayers of 69 literature references. We checked the Papp values for a total of 318 different compounds for the extractability of P0, considering possible limitations by aqueous boundary layers, paracellular transport, recovery issues, active transport, a possible proton flux limitation, and sink conditions. Overall, we were able to extract 77 reliable P0 values, which corresponds to about one quarter of the total compounds analyzed, while about half were limited by the diffusion through the aqueous layers. Compared to an existing data set of P0 values published by Avdeef, our approach resulted in a much higher exclusion of compounds. This is a consequence of stricter compound- and reference-specific exclusion criteria, but also because we considered possible concentration-shift effects due to different pH values in the aqueous layers, an effect only recently described in literature. We thus provide a consistent and reliable set of P0, e.g. as a basis for future modeling.

PBPK Model To Predict Marbofloxacin Distribution in Edible Tissues and Intestinal Exposure in Pigs

Marbofloxacin (MAR) is a fluoroquinolone antibiotic used in food-producing animals in European Union, especially in pigs. In this study, MAR concentrations in plasma, comestible tissues, and intestinal segments were determined in pigs injected with MAR. Based on these data and the literature, a flow-limited PBPK model was developed to predict the tissue distribution of MAR and estimate the withdrawal period after label-use in Europe. A submodel describing the different segments of the intestinal lumen was also developed to assess the intestinal exposure of MAR for the commensal bacteria. During model calibration, only four parameters were estimated. Then, Monte Carlo simulations were performed to generate a virtual population of pigs. The simulation results were compared with the observations from an independent data set during the validation step. A global sensitivity analysis was also carried out to identify the most influential parameters. Overall, the PBPK model was able to adequately predict the MAR kinetics in plasma and edible tissues, as well as in small intestines. However, the simulated concentrations in the large intestine were mostly underestimated, highlighting the need for improvements in the field of PBPK modeling to assess the intestinal exposure of antimicrobials in food animals.

The influence of immune stress induced by Escherichia coli lipopolysaccharide on the pharmacokinetics of danofloxacin in broilers

This study aimed to determine whether the challenge from Escherichia coli (E. coli) lipopolysaccharide (LPS) affects the pharmacokinetics of danofloxacin in broilers. Twenty 1-day-old Arbor Acres (AA) broilers were equally and randomly divided into 2 groups. When the chickens were 23, 25, 27, and 29 days old, E. coli LPS (1 mL; 0.5 mg/kg body weight [BW]) and sterile saline (1 mL) were intraperitoneally injected into the two groups. After the last injection, danofloxacin was given to all chickens by gavage at the dose of 5 mg/kg BW. Then serum and plasma samples at each time point were collected through the wing vein. Danofloxacin concentrations in plasma were detected through the high-performance liquid chromatography (HPLC) method and subjected to noncompartmental analysis using Phoenix software. The levels of chicken interleukin-1β (IL-1β) and corticosterone (CORT) in serum were measured by the Enzyme-linked immunosorbent assay (ELISA) kit. In addition, after the collection of plasma or serum samples, 7 chickens (31 days of age) in each group were killed to calculate the organ indices. Compared with the control group, the challenge of LPS significantly decreased the parameters of AUC_0-∞, C_max, and t_1/2λz and increased the parameters of T_max and λz. Additionally, in the LPS group, the absorption time of danofloxacin was prolonged; however, the elimination was accelerated, which resulted in reduced internal exposure.

Pharmacokinetic Behavior and Pharmacokinetic/Pharmacodynamic Integration of Danofloxacin Following Single or Co-Administration with Meloxicam in Healthy Lambs and Lambs with Respiratory Infections

The aim of this study was to determine the pharmacokinetics and pharmacodynamics of danofloxacin (DAN; 6 mg/kg) following subcutaneous administration alone or co-administration with meloxicam (MLX; 1 mg/kg) in healthy lambs and lambs with respiratory infections. The study was carried out using a total of four groups: HD (healthy; n = 6) and ID (infected; n = 7) groups who were administered DAN only, and HDM (healthy; n = 6) and IDM (infected; n = 7) groups who were administered DAN and MLX simultaneously. The plasma concentrations of DAN were determined using high-performance liquid chromatography–UV and analyzed by the non-compartmental method. DAN exhibited a similar elimination half-life in all groups, including both the healthy and infected lambs. The total clearance in the HDM, ID and IDM groups and volume of distribution in the HDM and IDM groups were significantly reduced. MLX in the IDM group significantly increased the area under the curve (AUC) and peak concentration (C_max) of DAN compared to the HD group. The Mannheimia haemolytica, Escherichia coli, and Streptococcus spp. strains were isolated from bronchoalveolar lavage fluid samples of the infected lambs. When co-administration with meloxicam, DAN at a 6 mg/kg dose can provide optimum values of ƒAUC_0–24/MIC (>56 h) and ƒC_max/MIC (>8) for susceptible M. haemolytica isolates with an MIC₉₀ value of 0.25 µg/mL and susceptible E. coli isolates with an MIC value of ≤0.125 µg/mL.

Pharmacokinetics and pharmacodynamics integration of danofloxacin against Eschrichia coli in piglet ileum ultrafiltration probe model

Improper use of antibiotics results in poor treatment and severe bacterial resistance. In this study, ultrafiltration probes were successfully placed in the ileum of piglets with the aid of anesthetic. After the fluoroquinolone antimicrobial drug danofloxacin (DAN) was intramuscularly administered, blood and ileum ultrafiltrate were collected at different time points and then determined by High Performance Liquid Chromatography (HPLC). Pharmacokinetics (PK) parameters for plasma and ileum ultrafiltrate were calculated by WinNonlin software. The DAN concentration in ileum ultrafiltrate was much higher than that in plasma during the period 1.2–48 h. The DAN concentration in plasma reached its maximum at 1.10 ± 0.03 h, but reached at 6.00 ± 0.00 h in the ileum ultrafiltrate. The mean C_max of the ileum is 13.59 times that of plasma. The elimination half-life (T_1/2β) in the ileum ultrafiltrate (6.84 ± 1.49 h) was shorter than those in plasma (7.58 ± 3.20 h). The MIC, MBC and MPC of DAN in MH broth against Escherichia coli (O₁₅₈) were 0.5 µg/mL, 0.5 µg/mL and 4 µg/mL, respectively. Both in vitro and ex vivo kill curves indicated that the killing mechanism of DAN against E. coli is concentration-dependent. The AUC/MPC ratio is 21.33 ± 2.14. Mean PK/PD index (AUC_24h/MIC) for ileum ultrafiltrate that achieved bacteriostatic, bactericidal, and eradication were 99.85, 155.57, and 218.02 h, respectively. Three different dosages (1.49 mg/kg, 2.42 mg/kg, and 3.24 mg/kg) were calculated respectively based on AUC_24h/MIC ratio above, which might provide a novel approach to the rational design of dosage schedules.

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 t 1 / 2 λ z , 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 t 1 / 2 λ z 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.

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.

Susceptibility breakpoint for Danofloxacin against swine Escherichia coli

Background

Improper use of antimicrobials results in poor treatment and severe bacterial resistance. Breakpoints are routinely used in the clinical laboratory setting to guide clinical decision making. Therefore, the objective of this study was to establish antimicrobial susceptibility breakpoints for danofloxacin against Escherichia coli (E.coli), which is an important pathogen of digestive tract infections.

Results

The minimum inhibitory concentrations (MICs) of 1233 E. coli isolates were determined by the microdilution broth method in accordance with the guidelines in Clinical and Laboratory Standards Institute (CLSI) document M07-A9. The wild type (WT) distribution or epidemiologic cutoff value (ECV) was set at 8 μg/mL with statistical analysis. Plasma drug concentration data were used to establish pharmacokinetic (PK) model in swine. The in vitro time kill test in our study demonstrated that danofloxacin have concentration dependent activity against E.coli. The PK data indicated that danofloxacin concentration in plasma was rapidly increased to peak levels at 0.97 h and remained detectable until 48 h after drug administration. The pharmacodynamic cutoff (CO_PD) was determined as 0.03 μg/mL using Monte Carlo simulation. To the best of our knowledge, this is the first study to establish the ECV and CO_PD of danofloxacin against E.coli with statistical method.

Conclusions

Compared to the CO_PD of danofloxacin against E.coli (0.03 μg/mL), the ECV for E.coli seemed reasonable to be used as the final breakpoint of danofloxacin against E.coli in pigs. Therefore, the ECV (MIC ≤8 μg/mL) was finally selected as the optimum danofloxacin susceptibility breakpoint for swine E.coli. In summary, this study provides a criterion for susceptibility testing and improves prudent use of danofloxacin for protecting public health.

Ciprofloxacin Enhances the Chemosensitivity of Cancer Cells to ABCB1 Substrates

ABCB1 is one of the major drug efflux transporters that is known to cause multidrug resistance (MDR) in cancer patients receiving chemotherapy for the treatment of solid tumors and hematological malignancies. Inhibition of ABCB1 efflux function is important for maintaining the intracellular concentration of chemotherapeutic drugs. Here, we evaluated ciprofloxacin for its ability to reverse MDR caused by the overexpression of ABCB1. Cytotoxicity of ciprofloxacin was determined by the MTT assay. The chemosensitizing effects of ciprofloxacin were determined in combination with ABCB1 substrates. The intracellular accumulation and efflux of ABCB1 substrates was measured by a scintillation counter, and protein expression was determined by the Western blotting. Vanadate-sensitive ATPase assay was performed to determine the effect of ciprofloxacin on the ATPase activity of ABCB1, and docking analysis was done to determine the interaction of ciprofloxacin with ABCB1. Ciprofloxacin significantly potentiated the cytotoxic effects of ABCB1 substrates in ABCB1-overexpressing cells. Furthermore, ciprofloxacin increased the intracellular accumulation and decreased the efflux of [³H]-paclitaxel without altering the expression of ABCB1. Ciprofloxacin stimulated the ATPase activity of ABCB1 in a concentration-dependent manner. Our findings showed that ciprofloxacin potently inhibits the ABCB1 efflux function and it has potential to be developed as a combination anticancer therapy.

Relationship between danofloxacin PK/PD parameters and emergence and mechanism of resistance of Mycoplasma gallisepticum in In Vitro model

Mycoplasma gallisepticum is a serious pathogen for poultry that causes chronic respiratory disease in chickens. Increased embryonic mortality, as well as reduced weight gain and egg production have been found in infected chickens, which can lead to considerable economic losses in poultry production. Increased antibiotic resistance compromises the use of tetracyclines, macrolides and quinolones in the farm environment. In the present study, danofloxacin concentrations were simulated below the MIC₉₉, between the MIC₉₉ and MPC (the mutant prevention concentration), and above the MPC in an in vitro dynamic model against M. gallisepticum. The relationship between the simulated danofloxacin pharmacokinetics, pharmacodynamics (PK/PD) parameters and development of resistance for M. gallisepticum was explored based on the available data obtained from various dosing regimens in the in vitro model. Danofloxacin concentration, counts of viable cell and susceptibility were determined during the experiment. The mutations in gyrA, gyrB, parC and parE as well as efflux pumps were examined. The MIC of danofloxacin against M. gallisepticum was increased when drug concentrations were between the lower and upper boundaries of the mutant selection window. The upper boundary of the selection window in vitro was estimated as a C_max/MPC value of 1. The lower boundary was estimated as C_max/MPC value of 0.05. Both in terms of the MIC and resistance frequency, M. gallisepticum resistance was developed when danofloxacin concentrations fell inside the mutant selection window (ratios of C_max to MPC between 0.05 and 1). The single mutation in gyrA (Ser-83→Arg) was found in all mutants, while double mutations in gyrA and parC (Ala-64→Ser) were observed only in the mutant with the highest MIC. In addition, no change of susceptibility in the mutants was observed in the presence of reserpine and carbonyl cyanide 3-chlorophenylhydrazone (CCCP). This suggested that ATP-binding cassette superfamily (ABC transporter) and major facilitator superfamily (MFS transporter) did not play a role in danofloxacin efflux.

Therapeutic Potential and Utility of Elacridar with Respect to P-glycoprotein Inhibition: An Insight from the Published In Vitro, Preclinical and Clinical Studies

The occurrence of efflux mechanisms via Permeability-glycoprotein (P-gp) recognized as an important physiological process impedes drug entry or transport across membranes into tissues. In some instances, either low oral bioavailability or lack of brain penetration has been attributed to P-gp mediated efflux activity. Therefore, the objective of development of P-gp inhibitors was to facilitate the attainment of higher drug exposures in tissues. Many third-generation P-gp inhibitors such as elacridar, tariquidar, zosuquidar, etc. have entered clinical development to fulfil the promise. The body of evidence from in vitro and in vivo preclinical and clinical data reviewed in this paper provides the basis for an effective blockade of P-gp efflux mechanism by elacridar. However, clinical translation of the promise has been elusive not just for elacridar but also for other P-gp inhibitors in this class. The review provides introspection and perspectives on the lack of clinical translation of this class of drugs and a broad framework of strategies and considerations in the potential application of elacridar and other P-gp inhibitors in oncology therapeutics.

Abcb1 in Pigs: Molecular cloning, tissues distribution, functional analysis, and its effect on pharmacokinetics of enrofloxacin

P-glycoprotein (P-gp) is one of the best-known ATP-dependent efflux transporters, contributing to differences in pharmacokinetics and drug-drug interactions. Until now, studies on pig P-gp have been scarce. In our studies, the full-length porcine P-gp cDNA was cloned and expressed in a Madin-Darby Canine Kidney (MDCK) cell line. P-gp expression was then determined in tissues and its role in the pharmacokinetics of oral enrofloxacin in pigs was studied. The coding region of pig Abcb1 gene was 3,861 bp, encoding 1,286 amino acid residues (Mw = 141,966). Phylogenetic analysis indicated a close evolutionary relationship between porcine P-gp and those of cow and sheep. Pig P-gp was successfully stably overexpressed in MDCK cells and had efflux activity for rhodamine 123, a substrate of P-gp. Tissue distribution analysis indicated that P-gp was highly expressed in brain capillaries, small intestine, and liver. In MDCK-pAbcb1 cells, enrofloxacin was transported by P-gp with net efflux ratio of 2.48 and the efflux function was blocked by P-gp inhibitor verapamil. High expression of P-gp in the small intestine could modify the pharmacokinetics of orally administrated enrofloxacin by increasing the Cmax, AUC and Ka, which was demonstrated using verapamil, an inhibitor of P-gp.

Potential pharmacokinetic effect of rifampicin on enrofloxacin in broilers: Roles of P-glycoprotein and BCRP induction by rifampicin

P-glycoprotein ( P-GP: , encoding gene Abcb1) and Breast Cancer Resistance Protein ( BCRP: , encoding gene Abcg2) are transport proteins that play a major role in modulating the bioavailability of oral drugs in humans and rodents. It has been shown that rifampicin is the typical inducer of P-gp in rodents by activating the nuclear receptor. However, its effect on Abcb1, Abcg2, CYP3A, and chicken xenobiotic-sensing orphan nuclear receptor ( CXR: ) mRNA expression in broilers is poorly understood. This study explored the effect of rifampicin on mRNA expression of Abcb1, Abcg2, CYP3A37, CXR as well as its effect on the pharmacokinetics of enrofloxacin in broilers. The mRNA levels of Abcb1, Abcg2, CYP3A37, and CXR were significantly increased in the liver (except Abcg2), kidney, jejunum, and ileum (P < 0.05) but not significantly changed in the duodenum (P > 0.05) after treated with rifampicin. Further analysis revealed that the variation tendencies of Abcb1, Abcg2, and CYP3A37 expression levels were significantly correlated with CXR mRNA expression levels in liver, kidney, jejunum, and ileum. Coadministration of rifampicin significantly changed the pharmacokinetic behavior of enrofloxacin orally administered by showing clearly lower AUC0-∞, AUC0-t, and Cmax as well as longer Tmax. The bioavailability of orally administered enrofloxacin was decreased from 72.5% to 24.8% by rifampicin. However, rifampicin did not significantly change the pharmacokinetics of enrofloxacin following intravenous administration. Our study shows that rifampicin up-regulated the small intestinal level of P-gp and BCRP and suggests that P-gp and BCRP are key factors that affected pharmacokinetic behavior of orally administered enrofloxacin by limiting its absorption from the intestine in broilers.

Intrabronchial Microdialysis: Effects of Probe Localization on Tissue Trauma and Drug Penetration into the Pulmonary Epithelial Lining Fluid

Recent intrabronchial microdialysis data indicate that the respiratory epithelium is highly permeable to drugs. Of concern is whether intrabronchial microdialysis disrupts the integrity of the respiratory epithelium and thereby alters drug penetration into the pulmonary epithelial lining fluid (PELF). The objective of this study was to investigate the effect of intrabronchial microdialysis on the integrity of the bronchial epithelium. Microdialysis sampling in PELF in proximal (n = 4) and distal bronchi (n = 4) was performed after intravenous inulin and florfenicol administration in anaesthetized pigs. Inulin was used as a marker molecule of permeability of the epithelium, and florfenicol was used as test drug. Bronchial tissue was examined by histopathology (distal and proximal bronchi) and gene expression analysis (RT-qPCR, proximal bronchi) at the termination of the experiment (6.5 hr). The microdialysis probe caused overt tissue trauma in distal bronchi, whereas no histopathological lesions were observed in proximal bronchi. A moderate up-regulation of the pro-inflammatory cytokines IL1B, IL6 and acute-phase reactant serum amyloid A was seen in proximal bronchi surrounding the microdialysis probes suggesting initiation of an inflammatory response. The observed up-regulation is considered to have limited impact on drug penetration during short-term studies. Inulin penetrated the respiratory epithelium in both proximal and distal bronchi without any correlation to histopathological lesions. Likewise, florfenicol penetration into PELF was unaffected by bronchial histopathology. However, this independency of pathology on drug penetration may not be valid for other antibiotics. We conclude that short-term microdialysis drug quantification can be performed in proximal bronchi without disruption of tissue integrity.

Intestinal drug transport: ex vivo evaluation of the interactions between ABC transporters and anthelmintic molecules

The family of ATP-binding cassette (ABC) transporters is composed of several transmembrane proteins that are involved in the efflux of a large number of drugs including ivermectin, a macrocyclic lactone (ML) endectocide, widely used in human and livestock antiparasitic therapy. The aim of the work reported here was to assess the interaction between three different anthelmintic drugs with substrates of the P-glycoprotein (P-gp) and the breast cancer resistance protein (BCRP). The ability of ivermectin (IVM), moxidectin (MOX) and closantel (CST) to modulate the intestinal transport of both rhodamine 123 (Rho 123), a P-gp substrate, and danofloxacin (DFX), a BCRP substrate, across rat ileum was studied by performing the Ussing chamber technique. Compared to the controls, Rho 123 efflux was significantly reduced by IVM (69%), CST (51%) and the positive control PSC833 (65%), whereas no significant differences were observed in the presence of MOX (30%). In addition, DFX efflux was reduced between 59% and 72% by all the assayed drug molecules, showing a higher potency than that observed in the presence of the specific BCRP inhibitor pantoprazole (PTZ) (52%). An ex vivo intestinal transport approach based on the diffusion chambers technique may offer a complementary tool to study potential drug interactions with efflux transporters such as P-gp and BCRP.

Age-related P-glycoprotein expression in the intestine and affecting the pharmacokinetics of orally administered enrofloxacin in broilers

Bioavailability is the most important factor for the efficacy of any drug and it is determined by P- glycoprotein (P-gp) expression. Confirmation of P-gp expression during ontogeny is needed for understanding the differences in therapeutic efficacy of any drug in juvenile and adult animals. In this study, Abcb1 mRNA levels in the liver and intestine of broilers during ontogeny were analysed by RT qPCR. Cellular distribution of P-gp was detected by immunohistochemstry. Age-related differences of enrofloxacin pharmacokinetics were also studied. It was found that broilers aged 4 week-old expressed significantly (P<0.01) higher levels of P-gp mRNA in the liver, jejunum and ileum, than at other ages. However, there was no significant (P>0.05) age-related difference in the duodenum. Furthermore, the highest and lowest levels of Abcb1 mRNA expression were observed in the jejunum, and duodenum, respectively. P-gp immunoreactivity was detected on the apical surface of the enterocytes and in the bile canalicular membranes of the hepatocytes. Pharmacokinetic analysis revealed that the 8 week-old broilers, when orally administrated enrofloxacin, exhibited significantly higher C_max (1.97 vs. 0.98 μg•ml^-1, P=0.009), AUC(14.54 vs. 9.35 μg•ml^-1•h, P=0.005) and Ka (1.38 vs. 0.43 h^-1, P=0.032), as well as lower T_peak (1.78 vs. 3.28 h, P=0.048) and T_1/2ka (0.6 vs. 1.64 h, P=0.012) than the 4 week-old broilers. The bioavailability of enrofloxacin in 8 week-old broilers was increased by 15.9%, compared with that in 4 week-old birds. Interestingly, combining verapamil, a P-gp modulator, significantly improved pharmacokinetic behaviour of enrofloxacin in all birds. The results indicate juvenile broilers had a higher expression of P-gp in the intestine, affecting the pharmacokinetics and reducing the bioavailability of oral enrofloxacin in broilers. On the basis of our results, it is recommended that alternative dose regimes are necessary for different ages of broilers for effective therapy.

Inhibition of ABCG2/BCRP transporter by soy isoflavones genistein and daidzein: effect on plasma and milk levels of danofloxacin in sheep

Danofloxacin is a synthetic fluoroquinolone antibacterial agent and a substrate for ATP-binding cassette transporter G2/breast cancer resistance protein (ABCG2/BCRP). This protein actively extrudes drugs from cells in the intestine, liver, kidney, and other organs, such as the mammary gland. The purpose of this study was to determine whether genistein and daidzein, isoflavones present in soy and known inhibitors of ABCG2, could diminish danofloxacin secretion into milk. The results obtained from BCRP-transduced MDCK-II cells (Mardin-Darby canine kidney) showed that both isoflavones efficiently inhibited the in vitro transport of the drug. In addition, danofloxacin transport into milk was studied in Assaf sheep. The experimental design with ewes (n = 18) included ewes fed with standard forage, soy-enriched forage for 15 days prior to the experiment or standard forage paired with orally administered exogenous genistein and daidzein. The danofloxacin levels in the milk of ewes in the soy-enriched diet group were decreased. The area under concentration-time curve AUC (0-24 h) was 9.3 ± 4.6 vs. 16.58 ± 4.44 μgh/mL in the standard forage or control group. The plasma levels of danofloxacin were unmodified. The AUC (0-24 h) milk/plasma ratio decreased by over 50% in the soy-enriched diet group, compared to the control group (4.90 ± 2.65 vs. 9.58 ± 2.17). Exogenous administration of isoflavones did not modify danofloxacin secretion into milk. This study showed that milk excretion of a specific substrate of BCRP, such as danofloxacin, can be diminished by the presence of isoflavones in the diet.

Pharmacokinetics, pharmacodynamics and therapeutics of pradofloxacin in the dog and cat

Pradofloxacin is a third-generation fluoroquinolone, licensed in the EU for use in a range of indications in the dog and cat and authorized more recently in the USA for one therapeutic indication (skin infections) in the cat. This review summarizes and appraises current knowledge on the physico-chemical, pharmacological [pharmacokinetics (PK) and pharmacodynamics (PD)], safety and therapeutic properties of pradofloxacin in the target species. Pradofloxacin contains two centres of asymmetry and is the pure SS enantiomer. After oral dosing of tablets (dog) or tablets and oral suspension (cat), maximum plasma concentrations (Cmax ) are achieved in less than 3.0 h, and terminal half-life is of the order of 5-10 h. Accumulation is slight or absent with once daily oral dosing. Free drug concentrations in plasma are in the range of 63-71% of total concentration. As for other fluoroquinolones, antibacterial activity is attributable to inhibition of bacterial replication at two sites, subunit A of topoisomerase II and topoisomerase IV. The antimicrobial spectrum includes gram-negative and gram-positive organisms, anaerobes, Mycoplasma spp. and some intracellular organisms (Rickettsia spp. and Mycobacterium spp.). The killing action is of the concentration-dependent type. Pradofloxacin has high potency (low MIC values) in comparison with first- and second-generation fluoroquinolones. Integration of in vivo PK and in vitro PD data provides values of Cmax /MIC and area under plasma concentration-time curve (AUC24 h )/MIC ratios predictive of good clinical efficacy against sensitive organisms, when administered at recommended dose rates. Clinical trial evaluation of pradofloxacin, in comparison with other authorized antimicrobial drugs, has demonstrated either noninferiority or superiority of pradofloxacin. Data indicating clinical and, in some instances, bacteriological cure have been reported: (i) in cats, for wound infections, abscesses, upper respiratory tract infections, conjunctivitis, feline infectious anaemia and lower urinary tract infections and (ii) in dogs, for wound infections, superficial and deep pyoderma, acute urinary tract infections and adjunctive treatment of infections of gingival and periodontal tissues. At clinical dose rates pradofloxacin was well tolerated in preclinical studies and in clinical trials. Among the advantages of pradofloxacin are (i) successful treatment of infections caused by strains resistant to some other fluoroquinolones, as predicted by PK/PD data, but depending on the specific MIC of the target strain and (ii) a reduced propensity for resistance development based on MPC measurements. The preclinical and clinical data on pradofloxacin suggest that this drug should commonly be the fluoroquinolone of choice when a drug of this class is indicated. However, the PK/PD data on pradofloxacin, in comparison with other fluoroquinolones, are not a factor that leads automatically to greater clinical efficacy.

In vitro and in vivo evidence for the importance of breast cancer resistance protein transporters (BCRP/MXR/ABCP/ABCG2)

The breast cancer resistance protein (BCRP/ABCG2) is a member of the G-subfamiliy of the ATP-binding cassette (ABC)-transporter superfamily. This half-transporter is assumed to function as an important mechanism limiting cellular accumulation of various compounds. In context of its tissue distribution with localization in the sinusoidal membrane of hepatocytes, and in the apical membrane of enterocytes ABCG2 is assumed to function as an important mechanism facilitating hepatobiliary excretion and limiting oral bioavailability, respectively. Indeed functional assessment performing mouse studies with genetic deletion or chemical inhibition of the transporter, or performing pharmacogenetic studies in humans support this assumption. Furthermore the efflux function of ABCG2 has been linked to sanctuary blood tissue barriers as described for placenta and the central nervous system. However, in lactating mammary glands ABCG2 increases the transfer of substrates into milk thereby increasing the exposure to potential noxes of a breastfed newborn. With regard to its broad substrate spectrum including various anticancer drugs and environmental carcinogens the function of ABCG2 has been associated with multidrug resistance and tumor development/progression. In terms of cancer biology current research is focusing on the expression and function of ABCG2 in immature stem cells. Recent findings support the notion that the physiological function of ABCG2 is involved in the elimination of uric acid resulting in higher risk for developing gout in male patients harboring genetic variants. Taken together ABCG2 is implicated in various pathophysiological and pharmacological processes.

Fluoroquinolone efflux mediated by ABC transporters

Quinolones and fluoroquinolones are broad spectrum bactericidal drugs, which are widely used in both human and veterinary medicine. These drugs can quite easily enter cells and are often used to treat intracellular pathogens. Some fluoroquinolones have been reported to undergo efflux, which could explain their low bioavailability. There is a growing need to understand resistance mechanisms to quinolones, involving for instance mutations or the action of efflux pumps. Several members of the ATP-binding cassette (ABC) drug efflux transporter family (MDR, MRP, ABCG2) significantly affect the pharmacokinetic disposition of quinolones. Active secretory mechanisms common to all fluoroquinolones have been suggested, as well as competition between fluoroquinolones at transporter sites. For grepafloxacin and its metabolites, MRP2 has been demonstrated to mediate biliary excretion. However, MDR1 is responsible for grepafloxacin intestinal secretion. Recently it has been shown that ciprofloxacin and enrofloxacin are efficiently transported ABCG2 substrates which are actively secreted into milk. It appears that multiple ABC transporters contribute to the overall secretion of fluoroquinolones. The objective of this work is to review the recent advances in insights into ABC transporters and their effects on fluoroquinolone disposition and resistance including data on drug secretion into milk.

Influence of systemic fluoroquinolone administration on the presence of Pasteurella multocida in the upper respiratory tract of clinically healthy calves

The influence of enrofloxacin administration (5 mg/kg) for five consecutive days on the occurrence of Pasteurella multocida in the upper respiratory tract of two healthy calves was monitored over a 10-day period. From nasal swabs of two additional healthy control calves, which received a placebo saline administration, P. multocida was isolated throughout the study period. In the enrofloxacin treated calves, P. multocida was not demonstrated in the nasopharynx from 48 h after the first injection until two days after the last administration, when P. multocida reappeared and proved to be clonal in nature to the original isolates. During the experiment, no change in minimal inhibitory concentration for enrofloxacin of the P. multocida isolates was detected (MIC < or = 0.015 microg/mL). Enrofloxacin concentrations were determined in the plasma by a high-performance liquid chromatography method with fluorescence detection. The PK/PD indices AUC/MIC and Cmax/MIC ratio were calculated and found to be 1157.7 and 129.8, respectively. Remarkably, the respiratory pathogen Arcanobacterium pyogenes became the predominant recovered organism in the nasopharynx of one animal following enrofloxacin therapy throughout the remaining of the experiment.

The Caco-2 cell monolayer: usefulness and limitations

BACKGROUND

The Caco-2 monolayer has been used extensively for the high-throughput screening of drug permeability and identification of substrates, inhibitors, and inducers of intestinal transporters, especially P-glycoprotein (P-gp). Traditionally, the Caco-2 monolayer is viewed as a single barrier rather than a polarized cell monolayer consisting of metabolic enzymes that are sandwiched between two membrane barriers with distinctly different transporters.

OBJECTIVE

This review addressed the usefulness and limitations of the Caco-2 cell monolayer in drug discovery and mechanistic studies.

METHODS

This mini-review covered applications of the Caco-2 monolayer, clarified misconceptions, and critically addressed issues on data interpretation.

CONCLUSION

The catenary model extends the usefulness of Caco-2 monolayer and provides proper mechanistic insight and data interpretation.

Implications of ABC transporters on the disposition of typical veterinary medicinal products

The ATP-Binding Cassette (ABC) transporters ABCB1, ABCC2 and ABCG2 are efflux transporters that facilitate the excretion of drugs, contribute to the function of biological barriers and maintain low cytoplasmic substrate concentrations in cells. ABC transporters modulate drug absorption, distribution and elimination according to the level of expression in the intestine, liver, kidney, and at biological barriers such as the blood-brain barrier. Moreover individual transporters are known to convey multi-drug resistance to tumour cells. While these diverse functions have been described in laboratory animal studies and in humans, the available information is very limited in animal species that are typical veterinary patients. This brief review summarizes the available data on organ distribution and expression levels in animals, genetic defects in dogs resulting in a non-functional P-gp expression, and describes examples of kinetic investigations directed to assess the clinical relevance of species differences in ABC-transporter expression.

Pharmacokinetics of pradofloxacin and doxycycline in serum, saliva, and tear fluid of cats after oral administration

The pharmacokinetic properties of pradofloxacin and doxycycline were investigated in serum, saliva, and tear fluid of cats. In a crossover study design, six cats were treated orally with a single dose of pradofloxacin (Veraflox Oral Suspension 2.5%) and doxycycline (Ronaxan 100 mg) at 5 mg/kg body weight. Following administration, samples of serum, saliva, and tear fluid were taken in regular intervals over a period of 24 h and analysed by turbulent flow chromatography/tandem mass spectrometry. All values are given as mean +/- SD. Pradofloxacin reached a mean maximum serum concentration (C(max)) of 1.1 +/- 0.5 microg/mL after 1.8 +/- 1.3 h (t(max)). In saliva and tear fluid, mean C(max) was 6.3 +/- 7.0 and 13.4 +/- 20.9 microg/mL, respectively, and mean t(max) was 0.5 +/- 0 and 0.8 +/- 0.3 h, respectively. Doxycycline reached a mean C(max) in serum of 4.0 +/- 0.8 microg/mL after 4.3 +/- 3.2 h. Whilst only at two time-points doxycycline concentrations close to the limit of quantification were determined in tear fluid, no detectable levels were found in saliva. The high concentrations of pradofloxacin in saliva and tear fluid are promising to apply pradofloxacin for the treatment of conjunctivitis and upper respiratory tract infections in cats. As doxycycline is barely secreted into these fluids after oral application the mechanisms of its clinical efficacy remain unclear.

Application and limitation of inhibitors in drug-transporter interactions studies

The objective of the present study was to investigate the reliability of transporter inhibitors in the elucidation of drug-transporter interactions when multiple transporters are present in a test system. The bidirectional permeabilities of digoxin, estrone-3-sulfate (E3S), and sulfasalazine, substrates of P-gp, BCRP/MRP2 and unspecified efflux transporters, respectively, were examined in Caco-2 and MDR-MDCK cells in the absence and presence of transporter inhibitors: CsA (P-gp), FTC (BCRP) and MK571 (MRP). Digoxin showed significant efflux ratios (ER) in both Caco-2 (ER=17) and MDR-MDCK (ER=120), whereas E3S and sulfasalazine only showed significant efflux in Caco-2 (ER=15 and 88, respectively) but not in MDR-MDCK cells (ER=1.1 and 1.3, respectively). CsA at 10 microM showed complete inhibition of digoxin efflux, partial inhibition of E3S efflux and no effect on sulfasalazine efflux. FTC and MK571 had different inhibitory effects on the efflux of these compounds. The present study shows evidence of the functional expression of multiple efflux transporter systems in Caco-2 cells. Although the use of Caco-2 cells and selected inhibitors of efflux transporters can provide useful mechanistic information on drug-drug interactions involving efflux transporters, the potential cross-reaction of inhibitors with multiple transporters makes it difficult to discern the role of individual transporters in drug transport or drug-drug interactions.

Functional studies on the activity of efflux transporters in an ex vivo model with chicken splenocytes and evaluation of selected fluoroquinolones in this model

The efflux proteins P-glycoprotein (P-gp), BCRP and members of the MRP-family (MRPs) are increasingly recognized as determinants of the absorption, tissue distribution and excretion of numerous drugs. A widely applied in vitro screening method, to assess the effect of these efflux transporters in transmembrane transport of drugs is based on the use of peripheral blood mononuclear cells (PBMC), in which the efflux of fluorescent dye Rhodamine 123 (Rh-123) can be easily measured. In avian species, the isolation of PBMCs is compromised by the presence of thrombocytes having approximately the same size. As an alternative, we validated the use of isolated splenocytes to assess Rhodamine 123 transport in the presence and absence of specific inhibitors for P-gp, MRPs and BCRP. Rh-123 efflux was concentration-dependent with the percentage of efflux that decreased with increasing concentrations. P-gp inhibitors, PSC833 and GF120918, significantly inhibit Rh-123 efflux, whereas inhibitors for MRPs and BCRP, MK571 and Ko-143, respectively, have a limited inhibitory effect. However, the effect of GF120918 was more pronounced as compared to PSC833, suggesting an additional role for BCRP next to P-gp in Rh-123 efflux. Moreover, fluoroquinolones were selected to test the applicability of the described model. None of these fluoroquinolones significantly inhibit P-gp function at concentrations up to 50 microM, with exception of danofloxacin and danofloxacin mesylate that were found to reduce Rh-123 efflux by approximately 15%.