Population pharmacokinetic modeling of the unbound levofloxacin concentrations in rat plasma and prostate tissue measured by microdialysis

Developmental stage and infection status may affect drug distribution in the prostate of rats

Prostate inflammation is often treated with drugs which are ineffective. Antibacterial agents fail to reach the prostate epithelium, and the blood-prostate barrier (BPB) may affect the drug transport process. Factors affecting drug efficacy remain unclear.Rats were categorised into groups A and B, corresponding to adulthood and puberty, respectively. Group C included the model of chronic prostate infection. Dialysates of levofloxacin and cefradine were collected from the prostate gland and jugular vein and evaluated. Pharmacokinetic analysis was conducted.The free concentrations of antimicrobials in the prostate and plasma samples of all groups peaked at 20 min, then gradually decreased. The mean AUC0-tprostate/AUC0-tplasma ratio in the levofloxacin group were 0.86, 0.53, and 0.95, and the mean values of AUC0-∞prostate/AUC0-∞plasma ratio were 0.85, 0.63, and 0.97. The corresponding values in the cefradine group were 0.67, 0.30 and 0.84, and 0.66, 0.31, and 0.85, respectively. The mean values in group B were lower than those in group A, and those in group C were higher than those in group B.The maturity of the prostate may affect the ability of the drug to cross the BPB. Infection may disrupt the BPB, affecting drug permeability.

Interspecies evaluation of a physiologically based pharmacokinetic model to predict the biodistribution dynamics of dendritic nanoparticles

The exposure of a dendritic nanoparticle and its conjugated active pharmaceutical ingredient (API) was determined in mouse, rat and dog, with the aim of investigating interspecies differences facilitating clinical translation. Plasma area under the curves (AUCs) were found to be dose proportional across species, while dose normalized concentration time course profiles in plasma, liver and spleen were superimposable in mouse, rat and dog. A physiologically based pharmacokinetic (PBPK) model, previously developed for mouse, was evaluated as a suitable framework to prospectively capture concentration dynamics in rat and dog. The PBPK model, parameterized either by considering species-specific physiology or using alternate scaling methods such as allometry, was shown to capture exposure profiles across species. A sensitivity analysis highlighted API systemic clearance as a key parameter influencing released API levels. The PBPK model was utilized to simulate human exposure profiles, which overlaid dose-normalized data from mouse, rat and dog. The consistency in measured interspecies exposures as well as the capability of the PBPK model to simulate observed dynamics support its use as a powerful translational tool.

Multiple drug transporters contribute to the brain transfer of levofloxacin

AIMS

The aim of this study was to assess the influence of the major transporters at blood-brain barrier and blood-cerebrospinal fluid barrier on levofloxacin (LVFX) pharmacokinetics in rat. To explore the different effects of transporters on drug concentrations in cerebrospinal fluid (CSF) and brain extracellular fluid (ECF).

METHODS

High-performance liquid chromatography coupled with microdialysis was used to continuously and synchronously measure unbound concentrations of LVFX in rat blood, hippocampal ECF, and lateral ventricle CSF for comprehensive characterization of brain pharmacokinetics. The role of transporters in the brain efflux mechanism of LVFX was analyzed in the absence and presence of various transporter inhibitors.

RESULTS

Following LVFX (50 mg/kg) administration, the unbound partition coefficient of LVFX in brain ECF and CSF (K_p,uu,ECF and K_p,uu,CSF ) were 34.0 ± 1.7% and 41.2 ± 2.4%, respectively. When probenecid was coadministered with LVFX, the AUC and the mean residence time (MRT) in rat blood increased significantly (p < 0.05). After MK571 intervention, 1.35-fold and 1.16-fold increases in K_p,uu,ECF and K_p,uu,CSF were observed, respectively (p < 0.05). Treatment with Ko143 increased the levels of LVFX in brain ECF. The difference in LVFX concentration in brain ECF and CSF was <3-fold with or without treatment with transporter inhibitors.

CONCLUSION

Efflux of LVFX from the central nervous system (CNS) involves multidrug resistance-associated proteins (MRPs), breast cancer resistance protein (BCRP), and organic anion transporters (OATs). MRPs play an important role in mediating the brain/CSF-to-blood efflux of LVFX. LVFX concentrations in CSF can be used as a surrogate to predict the concentrations inside brain parenchyma.

Quantitative Evaluation of Dendritic Nanoparticles in Mice: Biodistribution Dynamics and Downstream Tumor Efficacy Outcomes

A physiologically based pharmacokinetic model was developed to describe the tissue distribution kinetics of a dendritic nanoparticle and its conjugated active pharmaceutical ingredient (API) in plasma, liver, spleen, and tumors. Tumor growth data from MV-4-11 tumor-bearing mice were incorporated to investigate the exposure/efficacy relationship. The nanoparticle demonstrated improved antitumor activity compared to the conventional API formulation, owing to the extended released API concentrations at the site of action. Model simulations further enabled the identification of critical parameters that influence API exposure in tumors and downstream efficacy outcomes upon nanoparticle administration. The model was utilized to explore a range of dosing schedules and their effect on tumor growth kinetics, demonstrating the improved antitumor activity of nanoparticles with less frequent dosing compared to the same dose of naked APIs in conventional formulations.

Levofloxacin in veterinary medicine: a literature review

A potent third-generation antimicrobial fluoroquinolone drug, levofloxacin was introduced into human clinical practice in 1993. Levofloxacin is also used in veterinary medicine, however its use is limited: it is completely banned for veterinary use in the EU, and used extralabel in only companion animals in the USA. Since its introduction to clinical practice, many studies have been published on levofloxacin in animal species, including pharmacokinetic studies, tissue drug depletion, efficacy, and animal microbial isolate susceptibility to levofloxacin. This literature overview highlights the most clinically relevant and scientifically important levofloxacin studies linked to the field of veterinary medicine.

Efficacy of Human Exposures of Gepotidacin (GSK2140944) against Escherichia coli in a Rat Pyelonephritis Model

Gepotidacin is a first-in-class triazaacenaphthylene antibacterial that inhibits bacterial type II topoisomerases and has in vitro activity against a range of bacterial pathogens, including Escherichia coli Urinary tract infections often progress to pyelonephritis and are a worldwide problem due to the prevalence of multidrug-resistant E. coli strains. This study evaluated the in vivo efficacy of gepotidacin against four strains of multidrug-resistant E. coli in a rat pyelonephritis model. Infected rats received controlled intravenous infusions of gepotidacin every 12 h for 4 days that recreated human systemic exposures from oral gepotidacin (800 or 1,500 mg twice daily for 4 days). Liquid chromatography-tandem mass spectrometry analysis of blood samples and kidney homogenates showed that gepotidacin levels were 6- to 7-fold higher in kidneys than in blood. Across experiments with 4-day gepotidacin treatments, bacterial CFU in kidneys were reduced by 2.9 to 4.9 log₁₀ compared to pretreatment levels, and bladder CFU were reduced to the lower limit of detection (1.2 log₁₀). The efficacies of 800- and 1,500-mg gepotidacin exposures were statistically similar. A time-course experiment indicated that a period of more than 24 h of gepotidacin treatment was required for efficacy and that 4 days were needed for maximal response. Overall, these results demonstrate that the recreated human exposures of gepotidacin studied were effective in an animal model of pyelonephritis caused by multidrug-resistant E. coli and that further evaluation for clinical use is warranted.

Interaction Between Sex and Organic Anion-Transporting Polypeptide 1b2 on the Pharmacokinetics of Regorafenib and Its Metabolites Regorafenib-N-Oxide and Regorafenib-Glucuronide in Mice

Regorafenib, a multikinase inhibitor used in the treatment of various solid tumors, undergoes extensive uridine 5′‐diphosphate glucuronosyltransferase (Ugt)1a9‐mediated glucuronidation to form regorafenib‐N‐β‐glucuronide (M7; RG), but the contribution of hepatic uptake transporters, such as organic anion‐transporting polypeptide (Oatp)1b2, to the pharmacokinetics of regorafenib remains poorly understood. Using NONMEM‐based, population‐based, parent‐metabolite modeling, we found that Oatp1b2 and sex strongly impact the systemic exposure to RG in mice receiving oral regorafenib. Metabolic studies revealed that the liver microsomal expression of cytochrome P450 (Cyp)3a11 is twofold lower in female mice, whereas Ugt1a9 levels and function are not sex dependent. This finding is consistent with the metabolism of regorafenib occurring via two competing pathways, and the lack of Oatp1b2 results in decreased clearance of RG. The described model provides mechanistic insights into the in vivo disposition of regorafenib.

Use of microdialysis for the assessment of fluoroquinolone pharmacokinetics in the clinical practice

Antibacterial drugs, including fluoroquinolones, can exert their therapeutic action only with adequate penetration at the infection site. Multiple factors, such as rate of protein binding, drug liposolubility and organ blood-flow all influence ability of antibiotics to penetrate target tissues. Microdialysis is an in vivo sampling technique that has been successfully applied to measure the distribution of fluoroquinolones in the interstitial fluid of different tissues both in animal studies and clinical setting. Tissue concentrations need to be interpreted within the context of the pathogenesis and causative agents implicated in infections. Integration of microdialysis -derived tissue pharmacokinetics with pharmacodynamic data offers crucial information for correlating exposure with antibacterial effect. This review explores these concepts and provides an overview of tissue concentrations of fluoroquinolones derived from microdialysis studies and explores the therapeutic implications of fluoroquinolone distribution at various target tissues.

Population pharmacokinetic modeling to establish the role of P-glycoprotein on ciprofloxacin distribution to lung and prostate following intravenous and intratracheal administration to Wistar rats

Ciprofloxacin (CIP) is indicated for clinical treatment of urinary and respiratory tract infections. Poor infection site penetration and consequent insufficient exposure to the antimicrobial agent may be the reason for some therapeutic failures. Ciprofloxacin is reported as a substrate for efflux transporters, such as P-glycoprotein, which could be related to the presence of sub-therapeutic drug concentration at the infection site. In the present work we evaluated CIP pharmacokinetics (PK) in plasma and lung and prostate tissues of Wistar rats after intravenous (i.v.) and intratracheal (i.t.) dosing (7 mg/Kg) in the presence and absence of P-gp inhibitor tariquidar (TAR, 15 mg/Kg). Microdialysis was applied to determine free tissue concentration-time profiles and the obtained data were analyzed by non-compartmental and population PK (popPK) analysis. A sequential strategy was used to develop the popPK model: characterization of CIP PK in tissues (Tissue model) was performed subsequently to CIP PK modeling in plasma (Plasma model). Two and three compartmental models were used to simultaneously characterize plasma concentrations after i.t. and i.v. dosing; the distribution model was developed by separating the central compartment into venous and arterial compartment and by adding lung and prostate; TAR was identified as a significant covariate for clearance and volume of distribution of central compartment as well as for inter-compartmental clearance. Our results indicate an impact of P-gp on plasma PK, likely by acting on renal active secretion of CIP. Regarding CIP exposure in lung and prostate tissues, our results suggest a complex interplay between drug transporters; P-gp inhibition by TAR was likely counterbalanced by the activity of other efflux/influx transporters, which could not be fully characterized by our model.

Reducing Antibacterial Development Risk for GSK1322322 by Exploring Potential Human Dose Regimens in Nonclinical Efficacy Studies Using Immunocompetent Rats

Directly testing proposed clinical dosing regimens in nonclinical studies can reduce the risk during the development of novel antibacterial agents. Optimal dosing regimens can be identified in animal models by testing recreated human pharmacokinetic profiles. An example of this approach using continuous intravenous infusions of GSK1322322 in immunocompetent rats to evaluate recreated human exposures from phase I trials in pneumonia models with Streptococcus pneumoniae and Haemophilus influenzae and an abscess model with Staphylococcus aureus is presented. GSK1322322 was administered via continuous intravenous infusion to recreate 1,000- or 1,500-mg oral doses every 12 h in humans. Significant reductions (P ≤ 0.05 for all comparisons) in bacterial numbers compared with those for the baseline controls were observed for S. pneumoniae and H. influenzae (mean log₁₀ reductions, 1.6 to ≥2.7 and 1.8 to 3.3 CFU/lungs, respectively) with the recreated 1,000-mg oral dose. This profile was also efficacious against S. aureus (mean log₁₀ reduction, 1.9 to 2.4 CFU/abscess). There was a nonsignificant trend for improved efficacy against S. aureus with the 1,500-mg oral dose (mean log₁₀ reduction, 2.4 to 3.1 CFU/abscess). These results demonstrate that the human oral 1,000- or 1,500-mg exposure profiles of GSK1322322 recreated in rats were effective against representative community-associated pathogens and supported selection of the 1,500-mg oral dose given every 12 h for a phase II clinical skin infection study. Furthermore, this work exemplifies how the testing of recreated human pharmacokinetic profiles can be incorporated into the development process and serve as an aid for selecting optimal dosing regimens prior to conducting large-scale clinical studies.

Influence of Experimental Cryptococcal Meningitis in Wistar Rats on Voriconazole Brain Penetration Assessed by Microdialysis

To make advances in the treatment of cryptococcal meningitis, it is crucial to know a given drug's free fraction that reaches the biophase. In the present study, we applied microdialysis (μD) as a tool to determine the free levels reached by voriconazole (VRC) in the brains of healthy and Cryptococcus neoformans-infected rats. The infection was induced by the intravenous (i.v.) administration of 1 × 105 CFU of yeast. The dose administered was 5 mg/kg (of body weight) of VRC, given i.v. Plasma and microdialysate samples were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and LC-UV methods. The free brain/free plasma ratio (fT) and population pharmacokinetic (popPK) analyses were performed to evaluate the impact of infection on PK parameters of the drug. The brain penetration ratio showed an increase on brain exposure in infected animals (fThealthy = 0.85 versus fTinfected = 1.86). The structural PK model with two compartments and Michaelis-Menten (MM) elimination describes the VRC concentration-time profile in plasma and tissue simultaneously. The covariate infection was included in volume of distribution in the peripheral compartment in healthy animals (V2) and maximum rate of metabolism (VM ). The levels reached in infected tissues were higher than the values described for MIC of VRC for Cryptococccus neoformans (0.03 to 0.5 μg ml-1), indicating its great potential to treat meningitis associated with C. neoformans.

Population Pharmacokinetic Modeling as a Tool To Characterize the Decrease in Ciprofloxacin Free Interstitial Levels Caused by Pseudomonas aeruginosa Biofilm Lung Infection in Wistar Rats

Biofilm formation plays an important role in the persistence of pulmonary infections, for example, in cystic fibrosis patients. So far, little is known about the antimicrobial lung disposition in biofilm-associated pneumonia. This study aimed to evaluate, by microdialysis, ciprofloxacin (CIP) penetration into the lungs of healthy and Pseudomonas aeruginosa biofilm-infected rats and to develop a comprehensive model to describe the CIP disposition under both conditions. P. aeruginosa was immobilized into alginate beads and intratracheally inoculated 14 days before CIP administration (20 mg/kg of body weight). Plasma and microdialysate were sampled from different animal groups, and the observations were evaluated by noncompartmental analysis (NCA) and population pharmacokinetic (popPK) analysis. The final model that successfully described all data consisted of an arterial and a venous central compartment and two peripheral distribution compartments, and the disposition in the lung was modeled as a two-compartment model structure linked to the venous compartment. Plasma clearance was approximately 32% lower in infected animals, leading to a significantly higher level of plasma CIP exposure (area under the concentration-time curve from time zero to infinity, 27.3 ± 12.1 μg · h/ml and 13.3 ± 3.5 μg · h/ml in infected and healthy rats, respectively). Despite the plasma exposure, infected animals showed a four times lower tissue concentration/plasma concentration ratio (lung penetration factor = 0.44 and 1.69 in infected and healthy rats, respectively), and lung clearance (CL_lung) was added to the model for these animals (CL_lung = 0.643 liters/h/kg) to explain the lower tissue concentrations. Our results indicate that P. aeruginosa biofilm infection reduces the CIP free interstitial lung concentrations and increases plasma exposure, suggesting that plasma concentrations alone are not a good surrogate of lung concentrations.

A Review on Microdialysis Calibration Methods: the Theory and Current Related Efforts

Microdialysis is a sampling technique first introduced in the late 1950s. Although this technique was originally designed to study endogenous compounds in animal brain, it is later modified to be used in other organs. Additionally, microdialysis is not only able to collect unbound concentration of compounds from tissue sites; this technique can also be used to deliver exogenous compounds to a designated area. Due to its versatility, microdialysis technique is widely employed in a number of areas, including biomedical research. However, for most in vivo studies, the concentration of substance obtained directly from the microdialysis technique does not accurately describe the concentration of the substance on-site. In order to relate the results collected from microdialysis to the actual in vivo condition, a calibration method is required. To date, various microdialysis calibration methods have been reported, with each method being capable to provide valuable insights of the technique itself and its applications. This paper aims to provide a critical review on various calibration methods used in microdialysis applications, inclusive of a detailed description of the microdialysis technique itself to start with. It is expected that this article shall review in detail, the various calibration methods employed, present examples of work related to each calibration method including clinical efforts, plus the advantages and disadvantages of each of the methods.

Simultaneous Semimechanistic Population Analyses of Levofloxacin in Plasma, Lung, and Prostate To Describe the Influence of Efflux Transporters on Drug Distribution following Intravenous and Intratracheal Administration

Levofloxacin (LEV) is a broad-spectrum fluoroquinolone used to treat pneumonia, urinary tract infections, chronic bacterial bronchitis, and prostatitis. Efflux transporters, primarily P-glycoprotein (P-gp), are involved in LEV's tissue penetration. In the present work, LEV free lung and prostate interstitial space fluid (ISF) concentrations were evaluated by microdialysis in Wistar rats after intravenous (i.v.) and intratracheal (i.t.) administration (7 mg/kg of body weight) with and without coadministration of the P-gp inhibitor tariquidar (TAR; 15 mg/kg administered i.v.). Plasma and tissue concentration/time profiles were evaluated by noncompartmental analysis (NCA) and population pharmacokinetics (popPK) analysis. The NCA showed significant differences in bioavailability (F) for the control group (0.4) and the TAR group (0.86) after i.t. administration. A four-compartment model simultaneously characterized total plasma and free lung (compartment 2) and prostate (compartment 3) ISF concentrations. Statistically significant differences in lung and prostate average ISF concentrations and levels of kidney active secretion in the TAR group from those measured for the control group (LEV alone) were observed. The estimated population means were as follows: volume of the central compartment (V1), 0.321 liters; total plasma clearance (CL), 0.220 liters/h; TAR plasma clearance (CLTAR), 0.180 liters/h. The intercompartmental distribution rate constants (K values) were as follows: K12, 8.826 h(-1); K21, 7.271 h(-1); K13, 0.047 h(-1); K31, 7.738 h(-1); K14, 0.908 h(-1); K41, 0.409 h(-1); K21 lung TAR (K21LTAR), 8.883 h(-1); K31 prostate TAR (K31PTAR), 4.377 h(-1). The presence of P-gp considerably impacted the active renal secretion of LEV but had only a minor impact on the efflux from the lung following intratracheal dosing. Our results strongly support the idea of a role of efflux transporters other than P-gp contributing to LEV's tissue penetration into the prostrate.

Population pharmacokinetic modeling of cefadroxil renal transport in wild-type and Pept2 knockout mice

1. Cefadroxil is a broad-spectrum β-lactam antibiotic that is widely used in the treatment of various infectious diseases. Currently, poor understanding of the drug's pharmacokinetic profiles and disposition mechanism(s) prevents determining optimal dosage regimens and achieving ideal antibacterial responses in patients. In the present retrospective study, we developed a population pharmacokinetic model of cefadroxil in wild-type and Pept2 knockout mice using the nonlinear mixed effect modeling (NONMEM) approach. 2. Cefadroxil pharmacokinetics were best described by a two-compartment model, with both saturable and nonsaturable elimination processes to/from the central compartment. Through this modeling approach, pharmacokinetic parameters in wild-type and Pept2 knockout mice were well estimated, respectively, as follows: volume of central compartment V1 (3.43 versus 4.23 mL), volume of peripheral compartment V2 (5.98 versus 8.61 mL), intercompartment clearance Q (0.599 versus 0.586 mL/min) and linear elimination rate constant K10 (0.111 versus 0.070 min(-1)). Moreover, the secretion kinetics (i.e. V(m1) = 17.6 nmoL/min and K(m1) = 37.1 µM) and reabsorption kinetics (i.e. V(m2) = 15.0 nmoL/min and K(m2) = 27.1 µM) of cefadroxil were quantified in kidney, for the first time, under in vivo conditions. 3. Our model provides a unique tool to quantitatively predict the dose-dependent nonlinear disposition of cefadroxil, as well as the potential for transporter-mediated drug interactions.

Enhanced penetration of moxifloxacin into rat prostate tissue evidenced by microdialysis

Moxifloxacin is reported to have increased distribution into the prostate compared with older fluoroquinolones such as norfloxacin and ciprofloxacin, being able to reach tissue-to-plasma concentration ratios greater than unity. However, most of these studies use tissue homogenates derived from biopsy samples, which can lead to overestimation of free concentrations as fluoroquinolones tend to accumulate in the intracellular space. The aim of this study was to investigate moxifloxacin pharmacokinetics in rat prostate interstitial fluid by microdialysis. Tissue pharmacokinetics was assessed by implanting a small microdialysis catheter in the prostate gland. Blood samples were simultaneously collected for assessing plasma pharmacokinetics. Analysis of plasma (N=154) and microdialysis (N=344) concentrations after a single intravenous dose of 6 or 12mg/kg moxifloxacin was conducted in the non-linear mixed-effect modelling software NONMEM v.6 as well by a non-compartmental approach. Moxifloxacin showed a significant tissue distribution in the prostate (AUCprostate,ISF/fu·AUCplasma=1.24±0.37), 59% higher than the value obtained for levofloxacin in a previous study. A three-compartment model with non-linear kinetics could adequately describe moxifloxacin pharmacokinetics in terms of curve fitting and precision in parameter estimation. The developed pharmacokinetic model indicates that passive diffusion and active transport are the mechanisms involved in moxifloxacin distribution to the prostate. These findings suggest that moxifloxacin could be a better alternative to levofloxacin for the treatment of chronic bacterial prostatitis owing to its enhanced tissue penetration and higher AUCtissue/MIC ratios, even though it is not yet approved by the US FDA for this indication.