Pharmacokinetics of pefloxacin and its interaction with cyclosporin A, a P-glycoprotein modulator, in rat blood, brain and bile, using simultaneous microdialysis

Transporter modulation of molnupiravir and its metabolite β-D-N4-hydroxycytidine across the blood-brain barrier in a rat

BACKGROUND

The antiviral drug molnupiravir is an orally bioavailable prodrug of the nucleoside analog β-D-N4-hydroxycytidine (NHC), which is used to treat coronavirus disease 2019 (COVID-19). However, there is very little information on the barrier distribution of molnupiravir. Our hypothesis is that molnupiravir and NHC can penetrate the blood‒brain barrier (BBB) into brain tissue and that nucleoside transporters (equilibrative nucleoside transporters; ENT and concentrative nucleoside transporters; CNT) can modulate this process.

METHODS

To investigate the mechanism of molnupiravir transport through the BBB, multiple microdialyses coupled to a validated ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC‒MS/MS) was developed to monitor dialysates, and nitrobenzylthioinosine (NBMPR; an inhibitor of ENT) was administered concomitantly with molnupiravir (100 mg/kg, i.v.) in the male rat.

RESULTS

Here, we show that molnupiravir is rapidly metabolized to NHC in the blood and crossed the BBB in 20 min. Furthermore, when NBMPR is concomitantly administered to inhibit efflux, the concentrations of molnupiravir and NHC in the brain increased significantly.

CONCLUSIONS

In summary, molnupiravir rapidly transforms into NHC and crosses the BBB and reaches the brain at approximately 0.3-0.8% of the blood‒brain ratio. The maximum concentration of NHC in the blood and brain is above the average half maximal inhibitory concentration (IC50) of the drug required to treat severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, suggesting a therapeutic effect. The penetration of NHC is modulated by NBMPR. These findings provide constructive information on brain disorders in clinical patients with COVID-19.

Biotransformation and brain distribution of the anti-COVID-19 drug molnupiravir and herb-drug pharmacokinetic interactions between the herbal extract Scutellaria formula-NRICM101

The aim of this study was to explore the effects of herbal drug pharmacokinetic interactions on the biotransformation of molnupiravir and its metabolite β-D-N4-hydroxycytidine (NHC) in the blood and brain. To investigate the biotransformation mechanism, a carboxylesterase inhibitor, bis(4-nitrophenyl)phosphate (BNPP), was administered. Not only molnupiravir but also the herbal medicine Scutellaria formula-NRICM101 is potentially affected by coadministration with molnupiravir. However, the herb-drug interaction between molnupiravir and the Scutellaria formula-NRICM101 has not yet been investigated. We hypothesized that the complex bioactive herbal ingredients in the extract of the Scutellaria formula-NRICM101, the biotransformation and penetration of the bloodbrain barrier of molnupiravir are altered by inhibition of carboxylesterase. To monitor the analytes, ultrahigh-performance liquid chromatography tandem mass spectrometry (UHPLCMS/MS) coupled with the microdialysis method was developed. Based on the dose transfer from humans to rats, a dose of molnupiravir (100 mg/kg, i.v.), molnupiravir (100 mg/kg, i.v.) + BNPP (50 mg/kg, i.v.), and molnupiravir (100 mg/kg, i.v.) + the Scutellaria formula-NRICM101 extract (1.27 g/kg, per day, for 5 consecutive days) were administered. The results showed that molnupiravir was rapidly metabolized to NHC and penetrated into the brain striatum. However, when concomitant with BNPP, NHC was suppressed, and molnupiravir was enhanced. The blood-to-brain penetration ratios were 2% and 6%, respectively. In summary, the extract of the Scutellaria formula-NRICM101 provides a pharmacological effect similar to that of the carboxylesterase inhibitor to suppress NHC in the blood, and the brain penetration ratio was increased, but the concentration is also higher than the effective concentration in the blood and brain.

Transfer and biotransformation of the COVID-19 prodrug molnupiravir and its metabolite β-D-N4-hydroxycytidine across the blood-placenta barrier

BACKGROUND

Molnupiravir is an orally bioavailable prodrug of the nucleoside analogue β-D-N4-hydroxycytidine (NHC) and is used to treat coronavirus disease 2019 (COVID-19). However, the pharmacokinetics and transplacental transfer of molnupiravir in pregnant women are still not well understood. In the present study, we investigated the hypothesis that molnupiravir and NHC cross the blood-placenta barrier into the fetus.

METHODS

A multisite microdialysis coupled with a validated ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC‒MS/MS) system was developed to monitor the dialysate levels of molnupiravir and NHC in maternal rat blood and conceptus (the collective term for the fetus, placenta, and amniotic fluid). Molnupiravir was administered intravenously (100 mg/kg, i.v.) on gestational day 16. To investigate the mechanism of transport of molnupiravir across the blood-placenta barrier, we coadministered nitrobenzylthioinosine (NBMPR, 10 mg/kg, i.v.) to inhibit equilibrative nucleoside transporter (ENT).

FINDINGS

We report that molnupiravir is rapidly metabolized to NHC and then rapidly transformed in the fetus, placenta, amniotic fluid, and maternal blood. Our pharmacokinetics analysis revealed that the area under the concentration curve (AUC) for the mother-to-fetus ratio (AUCfetus/AUCblood) of NHC was 0.29 ± 0.11. Further, we demonstrated that the transport of NHC in the placenta may not be subject to modulation by the ENT.

INTERPRETATION

Our results show that NHC is the predominant bioactive metabolite of molnupiravir and rapidly crosses the blood-placenta barrier in pregnant rats. The NHC concentration in maternal blood and conceptus was above the average median inhibitory concentration (IC50) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), suggesting a therapeutic effect. These findings support the use of molnupiravir in pregnant patients infected with COVID.

FUNDING

This study was supported in part by research grants from the National Science and Technology Council of Taiwan (NSTC 111-2113-M-A49-018 and NSTC 112-2321-B-A49-005).

Transplacental transfer of acetaminophen in pregnant rats

Acetaminophen is among the most widely used analgesics; however, the proportion and mechanism of transplacental transfer of unbound acetaminophen with actual pharmacological activity remain unknown. Our hypothesis is that acetaminophen gradually penetrates the blood-placenta barrier to reach the fetus. A multiple microdialysis coupled to liquid chromatography with photodiode array detection method was developed to monitor acetaminophen levels in the maternal blood, placenta, fetus, and amniotic fluid of a pregnant rat and investigate this hypothesis. The pharmacokinetic data indicates that acetaminophen exhibits a nonlinear behavior in the maternal blood within the dosage regimen of 100 and 300 mg/kg. In addition, acetaminophen penetrates the placenta, fetus, and amniotic fluid during treatment. The transplacental transfer ratio represented by the area under the concentration curve (AUC) ratio for the conceptus (the collective term for the fetus, placenta, and amniotic fluid) and maternal blood (AUC_tissue/AUC_blood) was approximately 11-23 % after acetaminophen (100 and 300 mg/kg) administration. However, the transporter of multidrug resistance-associated protein (MRP) inhibitor MK-571 did not significantly change the transplacental transfer ratio. This basic study provides constructive information for the clinical application of acetaminophen in pregnant women.

Trans-placental transfer of nicotine: Modulation by organic cation transporters

Nicotine is a highly addictive substance and harmful to the developing foetus. However, few studies have investigated the transporter mechanism responsible for regulating the transfer of nicotine across the blood-placental interface. A multiple in-vivo microdialysis system coupled to ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was developed to monitor simultaneously nicotine and cotinine in the blood, placenta, foetus, and amniotic fluid of pregnant rats. The pharmacological mechanism of nicotine transfer across the placenta was investigated by co-administering corticosterone, an inhibitor of organic cation transporters (OCTs) that partly mediate the exchange of nicotine across the placenta. The results revealed that intravenously administered nicotine (1 mg/kg) was rapidly metabolised to cotinine with a transformation ratio (AUC_cotinine/AUC_nicotine) of 0.67 ± 0.08, 0.21 ± 0.05, 0.25 ± 0.12, 0.31 ± 0.05 in maternal blood, placenta, amniotic fluid, and foetus, respectively. The tissue transformation ratios (AUC_tissue/AUC_blood) were 0.83 ± 0.16, 0.65 ± 0.17, 0.57 ± 0.13 for nicotine, and 0.25 ± 0.06, 0.24 ± 0.12, 0.26 ± 0.04 for cotinine at placenta, amniotic fluid and foetus, respectively. Following the co-administration of corticosterone (2 mg/kg), the tissue transformation ratio of nicotine was significantly reduced in the placenta but was significantly increased in the foetus. Levels of cotinine were not significantly altered by the administration of corticosterone. These findings implicate OCT in mediating the transfer of nicotine across the blood-placenta barrier. Understanding the mechanism of nicotine transfer through the placenta may inform therapeutic strategies to lessen the exposure of the developing foetus to nicotine in the maternal bloodstream.

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.

Utility of Microdialysis in Infectious Disease Drug Development and Dose Optimization

Adequate drug penetration to a site of infection is absolutely imperative to ensure sufficient antimicrobial treatment. Microdialysis is a minimally invasive, versatile technique, which can be used to study the penetration of an antiinfective agent in virtually any tissue of interest. It has been used to investigate drug distribution and pharmacokinetics in variable patient populations, as a tool in dose optimization, a potential utility in therapeutic drug management, and in the study of biomarkers of disease progression. While all of these applications have not been fully explored in the field of antiinfectives, this review provides an overview of how microdialysis has been applied in various phases of drug development, a focus on the specific applications in the subspecialties of infectious disease (treatment of bacterial, fungal, viral, parasitic, and mycobacterial infections), and developing applications (biomarkers and therapeutic drug management).

Animal models in the pharmacokinetic/pharmacodynamic evaluation of antimicrobial agents

Animal infection models in the pharmacokinetic/pharmacodynamic (PK/PD) evaluation of antimicrobial therapy serve an important role in preclinical assessments of new antibiotics, dosing optimization for those that are clinically approved, and setting or confirming susceptibility breakpoints. The goal of animal model studies is to mimic the infectious diseases seen in humans to allow for robust PK/PD studies to find the optimal drug exposures that lead to therapeutic success. The PK/PD index and target drug exposures obtained in validated animal infection models are critical components in optimizing dosing regimen design in order to maximize efficacy while minimize the cost and duration of clinical trials. This review outlines the key components in animal infection models which have been used extensively in antibiotic discovery and development including PK/PD analyses.

Assessment of baicalin in mouse blood by monoclonal antibody-based icELISA

An indirect competitive enzyme-linked immunosorbent assay (icELISA) based on monoclonal antibaodies (MAb) was recently developed. This new method displays high sensitivity and accuracy, and is especially suitable for pharmacokinetic studies in small laboratory animals. This study aimed to develop an icELISA procedure for baicalin (BAL) quantitation in blood. We successfully developed the icELISA and applied in pharmacokinetic assays of Gegen Qinlian Decoction in mice. A linear correlation was obtained for BAL concentrations in the range from 34.69 to 2220.00 µg/L. The regression equation was y = 1.5557 - 0.4028log(C) with a correlation coefficient of 0.9936. Precision and accuracy of the icELISA method were evaluated by the variations between replicates from well to well (intra-assay) and plate to plate (inter-assay). The values obtained for these parameters were within the normal range (<15%). The recovery rates ranged from 98.93 to 126.78%, meeting the requirements for biological samples. Stability studies showed that BAL sample solutions were intact for 1 h, enough time for UV detection. However, long-term storage and especially freeze-thaw procedures were detrimental to BAL. The pharmacokinetic parameters derived from mouse experiments were as follows: area under the curves from time 0 to 48 h, 1876.15 ± 1108.14 mg h/L; mean maximum blood concentrations, 101.09 ± 31.53 mg/L; time of maximum concentration, 3.58 ± 2.88 h; mean residence time, 79.30 ± 61.21 h.

Biological analysis of herbal medicines used for the treatment of liver diseases

Herbal medicines have been used to treat liver disorders for thousands of years in the East and have now become a promising therapy internationally for pathological liver conditions. Biological analysis of hepatoprotective herbs is an important issue from the pharmacokinetic perspective in developing new therapeutic managements for liver disease. The biological analysis focuses on the pretreatment methods, separation and quantification of herbal medicines in biological samples. We have compiled and discuss the biological analytical method of six herbal medicines for liver protection containing Silybum marianum(silymarin), Glycyrrhiza glabra, Scutellaria baicalensis, Schisandra chinensis, Salvia miltiorrhiza and Astragalus membranaceus. This review provides a convenient reference for researchers to reduce time-consuming method optimization.

Analysis of biliary excretion of icariin in rats

Icariin is a bioactive herbal ingredient isolated from Epimedii Herba. This study evaluates the distribution of icariin in rats by microdialysis sampling and high-performance liquid chromatography with ultraviolet detection (HPLC-UV). Microdialysis probes were simultaneously placed in the jugular vein, brain striatum, and bile duct of each anesthetized rat for sampling after the administration of icariin (dose=10 or 20 mg/kg) via the femoral vein. The role of P-glycoprotein (P-gp) on icariin distribution was assessed by pretreatment with cyclosporine (CsA, dose=20 mg/kg). This study is the first report of the biliary excretion of icarin in rats, defined as the blood-to-bile distribution (k value), calculated by dividing the area under the concentration-time curve (AUC) of icariin in bile by that in blood (k=AUCbile/AUCblood). The k values were 19.0±5.9 and 18.8±3.8 at the doses of 10 and 20 mg/kg, respectively. The decreased biliary excretion of icariin due to pretreatment with CsA was evidenced by the reduced k values (18.8±3.8 vs 9.9±1.9, p=0.005). This work demonstrates that biliary excretion is the major elimination pathway for icariin disposition and that transporters, such as P-gp, might be related to icariin's biliary excretion.

Investigation of drug delivery by iontophoresis in a surgical wound utilizing microdialysis

PURPOSE

This study investigated the penetration of lidocaine around and through a sutured incision following the application of iontophoretic and passive patches in the CD Hairless rat.

MATERIALS AND METHODS

Concentrations in localized areas (suture, dermis, subcutaneous, and vascular) were determined using microdialysis sampling followed by analysis using liquid chromatography with UV detection.

RESULTS

Iontophoresis significantly enhanced the dermal penetration of lidocaine. In an intact skin model, dermal concentrations were 40 times greater following iontophoretic delivery compared to passive delivery. In a sutured incision model, iontophoresis enhanced localized concentrations in the dermis, suture, and subcutaneous regions by 6-, 15-, and 20-fold, respectively. Iontophoretic delivery to a region containing a sutured incision was focused to the incision resulting in a greater increase in the suture concentration and in the subcutaneous region directly below the incision.

CONCLUSIONS

The four microdialysis probe design was successful in the determination of localized drug penetration in a sutured incision model. Iontophoresis enhanced skin penetration and allowed for site specific delivery when applied to a sutured incision.

Liquid chromatographic method with amperometric detection to determine acteoside in rat blood and brain microdialysates and its application to pharmacokinetic study

A simple and sensitive liquid chromatography with amperometric detection was developed for the first time to monitor the protein-unbound acteoside in the rat blood and brain microdialysate by microdialysis technique. Microdialysis samples without further cleanup procedures were directly injected into the HPLC and separated using a reversed-phase C18 column (150 mmx2 mm, i.d. 5 microm) maintained at ambient temperature and a mobile phase comprised of acetonitrile-50 mM monosodium phosphate (pH 2.8) (17:83, v/v) with a flow rate of 0.2 mL/min. Based on the experimental voltamogram, the applied potential was set at +0.9 V oxidative mode. The concentration-response relationship was linear (r2>0.99) over a concentration range of 5-500 ng/mL; method precision and accuracy fell within predefined limits (less than 20%). The developed method was applied to assess the pharmacokinetics of acteoside, and the results suggested that acteoside was fitted better by the two-compartmental model following a single intravenous injection of acteoside. Acteoside was unable to be detected in the brain dialysate. The distribution and elimination half-lives of unbound acteoside in the blood were 5 and 28 min, respectively, which suggested the rapid distribution of acteoside.

Effect of Silibinin on the Pharmacokinetics of Pyrazinamide and Pyrazinoic Acid in Rats

Pyrazinamide (PZA) is widely used in combination with other drugs in chemotherapy for tuberculosis. However, the dose-related liver injury is the main adverse effect of PZA and its metabolite [pyrazinoic acid (PA)]. Silibinin is the main flavonoid extracted from milk thistle (Silybum marianum), and it displays hepatoprotective properties. This study investigates the pharmacokinetics of PZA and PA and their interaction with silibinin in rats. The parallel study design was divided into six groups: PZA alone, PZA + long-term silibinin exposure, PZA + concomitant short-term silibinin exposure, PA alone, PA + long-term silibinin exposure, and PA + concomitant short-term silibinin exposure groups. The results indicate that the distribution ratio of PZA from bile to blood [area under the curve (AUC)(bile)/AUC(blood)] in the PZA + long-term silibinin exposure and PZA + concomitant short-term silibinin exposure groups was also not significantly different when compared with the PZA alone group. However, the bile-to-blood distribution ratio of PA was significantly decreased in the PA + long-term silibinin exposure and the PA + concomitant short-term silibinin exposure groups. On PZA administration, the blood, but not bile, levels of PA were markedly increased in the PZA + long-term silibinin exposure and PZA + concomitant short-term silibinin exposure groups, but the bile-to-blood ratio of PA was decreased. These results suggest that the excretion pathway of PA may be blocked by silibinin through xanthine oxidase and hepatobiliary excretion.

Herb-drug interaction of Evodia rutaecarpa extract on the pharmacokinetics of theophylline in rats

The extract of Evodia rutaecarpa fruit and its preparation were used for the treatment of gastrointestinal disorders and headache. To assess the possible herb-drug interaction, the ethanol extract of Evodia rutaecarpa fruit (1 and 2 g/kg/day, p.o.) and the herbal preparation Wu-Chu-Yu-Tang (1 and 5 g/kg/day) were given to rats daily for three consecutive days and on the fourth day theophylline was administered (2 mg/kg, i.v.). Theophylline concentration in blood was measured by a microdialysis coupled to a liquid chromatographic system. Pharmacokinetic data were calculated by noncompartmental model. The results indicate that the theophylline level was significantly decreased by the pretreatment with the extract of Evodia rutaecarpa and herbal preparation Wu-Chu-Yu-Tang with dose-related manner. It is suggested that the herb-drug interaction may occur through the induction of the metabolism of theophylline.

Measurement of unbound cocaine in blood, brain and bile of anesthetized rats using microdialysis coupled with liquid chromatography and verified by tandem mass spectrometry

To investigate the disposition of unbound cocaine in the rat blood, brain and bile, we demonstrate an in vivo multiple sampling microdialysis system coupled with liquid chromatography for cocaine assay and verified by tandem mass spectrometry. Three microdialysis probes were concurrently inserted into the jugular vein, bile duct and brain striatum of each anesthetized rat. After a period of 2 h post-surgical stabilization, cocaine (10 mg kg(-1)) was administered through the femoral vein. Separation of unbound cocaine from various biological fluids was applied to a reversed-phase C(18) column (250 x 4.6 mm I.D., 5 microm). The mobile phase consisted of acetonitrile--10 mm potassium dihydrogen phosphate buffer (25:75, v/v, pH 4.0) and 0.8% diethylamine at a flow rate of 1 mL min(-1). The UV detector wavelength was set at 235 nm. The results indicate that cocaine penetrates the blood--brain barrier with a rapid distribution. However, unbound cocaine in the bile dialysate was not detectable in the UV detection. We therefore use LC--tandem mass spectrometry to detect the bile fluid after cocaine administration (3 mg kg(-1), i.v.). The results indicate that cocaine goes through hepatobiliary excretion.

Simultaneous determination of nicotine and its metabolite, cotinine, in rat blood and brain tissue using microdialysis coupled with liquid chromatography: Pharmacokinetic application

To elucidate the disposition of nicotine in the brain is important because the neuropharmacological effects from nicotine exposure are centrally predominated. The aim of the present study was to develop a rapid and simple method for the simultaneous determination of unbound nicotine and its main metabolite, cotinine, in rat blood and brain tissue. We coupled a multiple sites microdialysis sampling technique with HPLC-UV system to characterize the pharmacokinetics of both nicotine and cotinine. Microdialysis probes were inserted into the jugular vein/right atrium and brain striatum of Sprague-Dawley rats, and nicotine (2 mg/kg, i.v.) was administered via the femoral vein. Dialysates were collected every 10 min and injected directly into a HPLC system. Both nicotine and cotinine were separated by a phenyl-hexyl column (150 mm x 4.6 mm) from dialysates within 12 min. The mobile phase consisted of an acetonitrile-methanol-20 mM monosodium phosphate buffer (55:45:900, v/v/v, pH adjusted to 5.1) with a flow-rate of 1 ml/min. The wavelength of the UV detector was set at 260 nm. The limit of quantification for nicotine and cotinine were 0.25 microg/ml and 0.05 microg/ml, respectively. Intra- and inter-day precision and accuracy of both measurements fell well within the predefined limits of acceptability. The blood and brain concentration-time profile of nicotine and cotinine suggests that nicotine is easily to get into the central nervous system and cotinine exhibits a long retention time and accumulates in blood.

Measurement and pharmacokinetics of vincamine in rat blood and brain using microdialysis

Vincamine is an alkaloid compound derived from the Vinca minor plant. Since little is known concerning its pharmacokinetics and appropriate analytical method, this study focuses on its pharmacokinetics as well the possible roles of the multidrug transporter P-glycoprotein on its distribution and disposition. We develop a rapid and sensitive method using a microdialysis coupled with liquid chromatography for the concurrent determination of unbound vincamine in rat blood and brain. Microdialysis probes were simultaneously inserted into the jugular vein toward heart and brain hippocampus of male Sprague-Dawley rats for sampling in biological fluids following the administration of vincamine (10 and 30 mg/kg) through the femoral vein. Samples were eluted with a mobile phase containing methanol-1% diethylamine (pH 7.15) in water (75:25, v/v) and the flow rate of the mobile phase was 0.7 ml/min. Pharmacokinetic parameters of vincamine were derived using compartmental model. The decline of protein-unbound vincamine in the hippocampus and blood suggested that there was rapid exchange and equilibration between the peripheral compartment and the central nervous system. In the presence of cyclosporine, unbound vincamine levels in both blood and brain were significantly increased.

Determination and pharmacokinetic analysis of salvianolic acid B in rat blood and bile by microdialysis and liquid chromatography

Salvianolic acid B is an herbal ingredient isolated from Salvia miltiorrhiza. An in vivo microdialysis sampling method coupled to high-performance liquid chromatography has been developed for continuous monitoring of protein-unbound salvianolic acid B in rat blood and bile. Microdialysis probes were inserted into the jugular vein/right atrium and bile duct of Sprague-Dawley rats, and a dose of 100 mg/kg salvianolic acid B was then administered via the femoral vein. Dialysates were collected and directly injected into a liquid chromatographic system. Salvianolic acid B was eluted using a microbore reversed-phase ODS 5 microm (150 mm x 1 mm I.D.) column. Isocratic elution of salvianolic acid B was achieved within 10 min using the liquid chromatographic system. The chromatographic mobile phase consisted of acetonitrile-methanol-20 mM monosodium phosphoric acid (pH 3.5) (10:30:60, v/v/v) containing 0.1 mM 1-octanesulfonic acid with 0.05 ml/min. The wavelength of the UV detector was set at 290 nm. Salvianolic acid B in both blood and bile dialysates was adequately determined using the liquid chromatographic conditions described, although the blank bile pattern was more complex. The retention times of salvianolic acid B in rat blood and bile dialysates were found to be 7.2 min. Peak-areas of salvianolic acid B were linear (r2 > 0.995) over a concentration range of 0.1-50 microg/ml. In vivo recoveries of microdialysis probes of salvianolic acid B in rat blood and bile averaged 22 +/- 2% and 41 +/- 1%, respectively. This study indicates that salvianolic acid B undergoes hepatobiliary excretion.

Measurement of unbound ranitidine in blood and bile of anesthetized rats using microdialysis coupled to liquid chromatography and its pharmacokinetic application

To investigate the pharmacokinetics of unbound ranitidine in rat blood and bile, multiple microdialysis probes coupled to a liquid chromatographic system were developed. This study design was parallel in the following groups: the control-group of six rats received ranitidine alone (10 and 30 mg/kg, i.v.), the treated-group rats were co-administered with ranitidine and cyclosporine (P-glycoprotein (P-gp) inhibitor) or quinidine (both organic cation transport (OCT) and P-gp inhibitors) in six individual rats. Microdialysis probes were inserted into the jugular vein and the bile duct for blood and bile fluids sampling, respectively. Ranitidine in the dialysate was separated by a reversed-phase C18 column (Zorbax, 150 mm x 4.6 mm i.d.; 5 microm) maintained at ambient temperature. Samples were eluted with a mobile phase containing acetonitrile-methanol-tetrahydrofuran-20 mM K2HPO4 (pH 7.0) (24:20:10:946, v/v), and the flow rate of the mobile phase was 1 ml/min. The optimal UV detection for ranitidine was set at wavelength 315 nm. Between 20 and 30 min after drug administration (10 or 30mg/kg), the ranitidine reached the maximum concentration in the bile. The bile-to-blood distribution ratio (AUC(bile)/AUC(blood)) was 9.8 +/- 1.9 and 13.9 +/- 3.8 at the dosages of 10 and 30 mg/kg, respectively. These studies indicate that ranitidine undergoes hepatobiliary excretion which against concentration gradient from bile-to-blood. In addition, the AUC of ranitidine in bile decreased in the treatment of cyclosporine or quinidine, which suggests that the hepatobiliary excretion of ranitidine was partially regulated by P-glycoprotein or organic cation transporter.

Hepatobiliary excretion of berberine

Berberine is a bioactive herbal ingredient isolated from the roots and bark of Berberis aristata or Coptis chinensis. To investigate the detailed pharmacokinetics of berberine and its mechanisms of hepatobiliary excretion, an in vivo microdialysis coupled with high-performance liquid chromatography was performed. In the control group, rats received berberine alone; in the drug-treated group, 10 min before berberine administration, the rats were injected with cyclosporin A (CsA), a P-glycoprotein (P-gp) inhibitor; quinidine, both organic cation transport (OCT) and P-gp inhibitors; SKF-525A (proadifen), a cytochrome P450 inhibitor; and probenecid to inhibit the glucuronidation. The results indicate that berberine displays a linear pharmacokinetic phenomenon in the dosage range from 10 to 20 mg kg(-1), since a proportional increase in the area under the concentration-time curve (AUC) of berberine was observed in this dosage range. Moreover, berberine was processed through hepatobiliary excretion against a concentration gradient based on the bile-to-blood distribution ratio (AUC(bile)/AUC(blood)); the active berberine efflux might be affected by P-gp and OCT since coadministration of berberine and CsA or quinidine at the same dosage of 10 mg kg(-1) significantly decreased the berberine amount in bile. In addition, berberine was metabolized in the liver with phase I demethylation and phase II glucuronidation, as identified by liquid chromatography/tandem mass spectrometry. Also, the phase I metabolism of berberine was partially reduced by SKF-525A treatment, but the phase II glucuronidation of berberine was not obviously affected by probenecid under the present study design.

Concurrent determination of thalidomide in rat blood, brain and bile using multiple microdialysis coupled to liquid chromatography

A rapid and sensitive system of liquid chromatography coupled with microdialysis was developed for the simultaneous determination of unbound thalidomide in rat blood, brain and bile for pharmacokinetic study. Microdialysis probes were concurrently inserted into the jugular vein toward the right atrium, the brain striatum and the bile duct of the anesthetized Sprague-Dawley rats for biological fluid sampling after the administration of thalidomide (5 mg kg(-1)) through the femoral vein. Thalidomide and dialysates were separated using a Zorbax ODS C(18) column and a mobile phase comprising acetonitrile-methanol-0.1 mm 1-octanesulufonic acid (32:3:65, v/v/v, pH 5.3) at flow rate of 1 mL min(-1). The UV wavelength was set at 220 nm. The concentration-response relationship was linear (r(2)>0.995) over a concentration range of 0.025--25 microg mL(-1). The intra-assay and inter-assay precision and accuracy of thalidomide fell within 7%. The average in vivo recoveries were 0.31+/- 0.02,0.046+/- 0.004 and 0.57+/- 0.02 (n=6), respective to the dialysates of blood, brain and bile, with thalidomide at concentrations 2, 5 and 10 microg mL(-1). The disposition of thalidomide in the blood, brain and bile fluid suggests that there is a rapid thalidomide exchange and equilibration between the blood and brain systems. In addition, thalidomide undergoes hepatobiliary excretion.

Determination of (-)-epigallocatechin gallate in rat blood by microdialysis coupled with liquid chromatography

A liquid chromatographic method coupled with microdialysis was used to determine the protein-unbound (-)-epigallocatechin-3-gallate (EGCG) in rat blood. EGCG and dialysates were separated using a Merck RP-18e column maintained at ambient temperature, and a mobile phase comprised of acetonitrile-10 mM monopotassium phosphate (pH 3.82) (20:80, v/v) with a flow rate of 1.0 ml/min. The UV detector wavelength was set at 206 nm. The detection limit for EGCG was 10 ng/ml. The concentration-response relationship was linear (r2 > 0.995) over a concentration range of 0.05-10 microg/ml; intra- and inter-assay precision and accuracy of EGCG fell within predefined limits. Pharmacokinetic parameters of EGCG were assessed using compartmental models. The disposition of EGCG in the rat blood suggests that EGCG was fitted by two-compartmental model. The distribution and elimination half-lives were 6 and 72 min respectively, after the dosage of 30 mg/kg.

Determination of unbound theophylline in rat blood and brain by microdialysis and liquid chromatography

To investigate the mechanism by which theophylline crosses the blood-brain barrier (BBB) and its disposition, we determined unbound theophylline in rat blood and brain using microbore liquid chromatography coupled with microdialysis. Microdialysis probes were inserted into the jugular vein and the brain striatum of male Sprague-Dawley rats. Then theophylline at dosage of 10 or 30 mg/kg was administered through the femoral vein. Theophylline and dialysates were separated using a microbore phenyl-hexyl column (150 mm x 1 mm, 5 microm). The mobile phase comprised of acetonitrile-methanol-10 mM monosodium phosphate (pH 3.0) (10:20:70, v/v/v). The UV wavelength was set at 270 nm. The concentration-response relationship was linear over a concentration range of 0.05-50 microg/ml; intra-assay and inter-assay precision and accuracy of theophylline fell within 10%. Average in vivo recoveries were 0.74 +/- 0.06 in blood and 0.27 +/- 0.07 in brain with theophylline at concentrations 1, 2 and 5 microg/ml. This biological sampling method thereby allowed the determination of theophylline levels in blood and brain tissues. The disposition of theophylline in the blood and brain tissue suggests that there was rapid exchange and equilibration between the blood and brain system. The drug-drug interaction results indicate that theophylline was able to cross BBB, but that it might not be regulated by p-glycoprotein to the pharmacokinetics of theophylline.

Assaying protein unbound drugs using microdialysis techniques

Compared with traditional sampling methods, microdialysis is a technique for protein unbound drug sampling without withdrawal of biological fluids and involving minimal disturbance of physiological function. Conventional total drug sample consists of unbound drugs and protein bound drugs, which are loosely bound to plasma proteins such as albumin and alpha-1 acid glycoprotein, forming an equilibrium ratio between bound and unbound drugs. However, only the unbound fraction of drug is available for absorption, distribution, metabolism and elimination, and delivery to the target sites for pharmacodynamic actions. Although several techniques have been used to determine protein unbound drugs from biological fluids, including ultrafiltration, equilibrium dialysis and microdialysis, only microdialysis allows simultaneous sampling of protein unbound chemicals from plasma, tissues and body fluids such as the bile juice and cerebral spinal fluid for pharmacokinetic and pharmacodynamic studies. This review article describes the technique of microdialysis and its application in pharmacokinetic studies. Furthermore, the advantages and limitations of microdialysis are discussed, including the detailed surgical techniques in animal experiments from rat blood, brain, liver, bile duct and in vitro cell culture for unbound drug analysis.

Regulation of hepatobiliary excretion of sinomenine by P-glycoprotein in Sprague-Dawley rats

Sinomenine, an herbal ingredient isolated from Sinomenium acutum, is used for the amelioration of arthritis. Using microdialysis and a specially constructed hepato-duodenal shunt probe, the present study investigated the pharmacokinetics of sinomenine in rat blood and bile and the effects of P-glycoprotein modulation and cytochrome P450 inhibition. The results indicated that the pharmacokinetics of sinomenine in rat blood appeared to be dose dependent in the 3 to 30 mg/kg range. The disposition of sinomenine in the bile exhibited a slow elimination phase, reaching a peak concentration in 20-40 min following intravenous administration. The area under the concentration versus time curves (AUC's) for sinomenine in the bile were significantly greater than those in the blood at dosages of 3, 10, and 30 mg/kg with the blood-to-bile distribution ratios (k = AUC(bile) / AUC(blood)) being 3.85 +/- 0.29 and 3.52 +/- 0.28 at 10 and 30 mg/kg, respectively, indicating active hepatobiliary excretion. Coadministration with 20 mg/kg of cyclosporin A 10 min prior to sinomenine administration resulted in a significant reduction of the bile AUC's for the dosages of 10 and 30 mg/kg., resulting in the bile/blood distribution ratio being significantly reduced to 0.47 +/- 0.05 and 0.49 +/- 0.05, respectively. On the other hand, proadifen treatment increased both the blood and bile AUC's, resulting in insignificant effects on the blood-to-bile distribution ratios. In conclusion, our results indicated that sinomenine underwent active hepatobiliary elimination which may be regulated by the P-glycoprotein and that P-450 was likely involved in its metabolism.

Pharmacokinetic study of free mangiferin in rats by microdialysis coupled with microbore high-performance liquid chromatography and tandem mass spectrometry

Mangiferin (2-beta-D-glucopyranosyl-1,3,6,7-tetrahydroxyxanthen-9-one) has been isolated from the herbal root of Anemarrhena asphodeloides Bung showing antioxidative, antiviral, and anticancer effect. An in vivo microdialysis sampling method coupled to microbore high-performance liquid chromatography (HPLC) was employed for continuous monitoring of free mangiferin in rat blood. Microdialysis probes were inserted into the jugular vein/right atrium and brain striatum of Sprague-Dawley rats, and mangiferin at doses of 10, 30 or 100 mg/kg were then administered via the femoral vein. Dialysates were collected every 10 min and injected directly into a microbore HPLC system. Mangiferin was separated by a reversed-phase C18 microbore column (150 x 1 mm) from dialysate within 10 min. The mobile phase consisted of acetonitrile-0.05% phosphoric acid-tetrahydrofuran (10:75:15, v/v/v) with a flow-rate of 0.05 ml/min. The wavelength of the UV detector was set at 257 nm. The limit of quantification for mangiferin was 0.05 microg/ml and in vivo recovery of mangiferin at concentrations of 1, 5 and 10 microg/ml was in range of 37.7-39.8%. The results indicate that the pharmacokinetics of mangiferin at doses of 10-30 mg/kg reveals a linear relation, while doses of 30-100 mg/kg show a nonlinear pharmacokinetic phenomenon. Mangiferin was undetectable in brain dialysate. The proposed method provides a technique for rapid and sensitive analysis of free mangiferin in rat blood and further application in pharmacokinetic study. Furthermore, the metabolites of mangiferin in the rat bile were confirmed by LC electrospray ionization (ESI) tandem mass spectrometry (MS-MS).

Pharmacokinetics of metronidazole in rat blood, brain and bile studied by microdialysis coupled to microbore liquid chromatography

Metronidazole is a synthetic nitroimidazole-derived antibacterial and antiprotozoal agent used for the treatment of infections involving gram-negative anaerobes. The aim of this study is to develop an in vivo microdialysis with microbore high-performance liquid chromatographic system for the pharmacokinetic study of metronidazole in rat blood, brain and bile. In addition, to investigate the disposition mechanism of metronidazole, the P-glycoprotein modulator and cytochrome P450 inhibitor were concomitantly administered. Separation of metronidazole from various biological fluids was applied to a microbore reversed-phase ODS 5 microm (150 x 1 mm I.D.) column. Its mobile phase consists of an acetonitrile-50 mM monosodium phosphate buffer (pH 3.0) containing 0.1% triethylamine (10:90, v/v) with a flow-rate of 0.05 ml/min. The UV detector wavelength was set at 317 nm. The results suggest that metronidazole penetrates the blood-brain barrier (BBB) and goes through hepatobiliary excretion. However, these pathways of BBB penetration and hepatobiliary excretion of metronidazole may not be related to the P-glycoprotein.

Drug efflux transporters in the CNS

The central nervous system (CNS) contains important cellular barriers that maintain homeostasis by protecting the brain from circulating toxins and through the elimination of toxic metabolites generated in the brain. The barriers that limit the concentration of toxins and xenobiotics in the interstitial fluids of the CNS are the capillary endothelial cells of the blood-brain barrier (BBB) and the epithelial cells of the blood-cerebrospinal fluid barrier (BCSFB). Both of these barriers have cellular tight junctions and express transport systems which serve to actively transport nutrients into the brain, and actively efflux toxic metabolites and xenobiotics out of the brain. This review will focus on the expression and function of selected drug efflux transporters in these two barriers, specifically the multidrug resistance transporter, p-glycoprotein, and various organic anion transporters, such as multidrug resistance-associated proteins, organic anion transporter polypeptides, and organic anion transporters. These transport systems are increasingly recognized as important determinants of drug distribution to, and elimination from, different compartments of the CNS. Consequences of drug efflux transporters in barriers of the CNS include limiting the distribution of substrates that are beneficial to treat CNS diseases, and increasing the possibility of drug-drug interactions that may lead to untoward toxicities. Therefore, the study of these transporters is important in examining the various determinants of drug delivery to the CNS.

The effects of the cyclosporin A, a P-glycoprotein inhibitor, on the pharmacokinetics of baicalein in the rat: a microdialysis study

1. Baicalein is a bioactive flavonoid isolated from the root of Scutellaria baicalensis Georgi, a medicinal herb that has been used since ancient times to treat bacterial infections. As little is known concerning its pharmacokinetics, this study focussed on its pharmacokinetics as well as the possible roles of the multidrug transporter P-glycoprotein on its distribution and disposition. 2. Three microdialysis probes were simultaneously inserted into the jugular vein, the hippocampus and the bile duct of male Sprague-Dawley rats for sampling in biological fluids following the administration of baicalein (10, 30 and 60 mg kg(-1)) through the femoral vein. The P-glycoprotein inhibitor cyclosporin A was used to help delineate its roles. 3. The study design consisted of two groups of six rats in parallel: control rats which received baicalein alone and the cyclosporin A treated-group in which the rats were injected cyclosporin A, a P-glycoprotein inhibitor, 10 min prior to baicalein administration. 4. Cyclosporin A treatment resulted in a significant increase in elimination half-life, mean residence time and area under the concentration versus time curve (AUC) of unbound baicalein in the brain. However, AUC in the bile was decreased. 5. The decline of baicalein in the hippocampus, blood and bile suggested that there was rapid exchange and equilibration between the peripheral compartment and the central nervous system. In addition, the results indicated that baicalein was able to penetrate the blood-brain barrier as well as undergoing hepatobiliary excretion. 6. Although no direct transport studies were undertaken and multiple factors may affect BBB penetration and hepatobiliary excretion, strong association of the involvement of P-glycoprotein in these processes is indicated.

Hepatobiliary excretion of fluconazole and its interaction with cyclosporin A in rat blood and bile using microdialysis

In order to investigate the hepatobiliary excretion of Fluconazole, we develop a rapid and sensitive method using high-performance liquid chromatography coupled with microdialysis for the simultaneous determination of unbound fluconazole in rat blood and bile. Microdialysis probes were inserted into both the jugular vein toward the right atrium and bile duct of male Sprague-Dawley rats for biological fluid sampling after administration of fluconazole at 10 mg/kg through the femoral vein. Fluconazole and dialysates were separated using a Zorbax phenyl column maintained at ambient temperature. The detection limit of fluconazole was 50 ng/ml. Biological fluid sampling thereby allowed the simultaneous determination of fluconazole levels in blood and bile. The disposition of fluconazole in the blood and bile fluid suggests that there was rapid exchange and equilibration between the blood and hepatobiliary system. In addition, to investigate the mechanism of P-glycoprotein related hepatobiliary excretion of fluconazole, we examined the drug-drug interaction of fluconazole and cyclosporin A in the aspect of pharmacokinetics. These results indicate that the plasma level of fluconazole was no different than that in bile, and that fluconazole undergoes hepatobiliary excretion, maybe unrelated to the P-glycoprotein transported system.

Pharmacokinetic study of levofloxacin in rat blood and bile by microdialysis and high-performance liquid chromatography

The aim of this study was to develop a rapid and sensitive method for the simultaneous determination of unbound levofloxacin in rat blood and bile using high-performance liquid chromatography coupled with microdialysis for further pharmacokinetic study. Microdialysis probes were simultaneously inserted into the jugular vein toward the right atrium and the bile duct of male Sprague-Dawley rats for biological fluid sampling after administration of levofloxacin 3 mg/kg through the femoral vein. Levofloxacin and dialysates were separated using a Merck LiChrospher reversed-phase C18 column maintained at ambient temperature. The mobile phase was comprised of acetonitrile-1 mM 1-octanesulfonic acid (40:60, v/v, pH 3.0 adjusted with orthophosphoric acid). The fluorescence response for levofloxacin was observed at excitation and emission wavelengths of 292 and 494 nm, respectively. The detection limit of levofloxacin was 50 ng/ml. Intra-day and inter-day precision and accuracy of levofloxacin measurements fell well within the predefined limits of acceptability. The disposition of levofloxacin in the blood and bile fluid suggests that there was rapid exchange and equilibration between the blood and hepatobiliary systems, and the plasma level of levofloxacin was greater than that of the bile. Thus, levofloxacin undergoes hepatobiliary excretion but might not be related to the P-glycoprotein transport system.

Determination of diclofenac in rat bile and its interaction with cyclosporin A using on-line microdialysis coupled to liquid chromatography

Diclofenac is a potent inhibitor of prostaglandin synthesis, as well as an established antipyretic and analgesic agent. To determine diclofenac in rat bile and investigate its hepatobiliary excretion, a procedure using rapid and sensitive high-performance liquid chromatography coupled to microdialysis sampling system was developed. A shunt linear microdialysis probe was inserted into the common bile duct between the liver and the duodenum for continuous sampling of the drug from bile fluids following intravenous administration of diclofenac (1 mg/kg). Separation and quantitation of diclofenac in the bile dialysates were achieved using a microbore reversed-phase C18 column (150x1.0 mm I.D.; particle size 5 microm) maintained at ambient temperature. Samples were eluted with a mobile phase containing 100 mM sodium dihydrogenphosphate (pH 3.1)-acetonitrile (30:70, v/v), and the flow-rate of the mobile phase was 0.05 ml/min. The UV detector wavelength was set at 280 nm. The concentration-response relationship from the present method indicated linearity (r2>0.995) over a concentration range of 5-5000 ng/ml for diclofenac. Intra-assay and inter-assay precision and accuracy of diclofenac fell well within the predefined limits of acceptability (< or = 15%). The diclofenac in rat bile appeared to have a slow elimination phase, with a peak concentration at 20 min following diclofenac administration. The results demonstrated that diclofenac might be secreted into bile in unconjugated form by a canalicular bile acid transporter, and then go through hepatobiliary excretion. These results may provide good clinical evidence showing the value of diclofenac for the treatment of biliary colic. The elimination half-life of diclofenac in the biliary elimination was prolonged by treatment with cyclosporin A, indicating that the drug-drug interaction might affect the hepatobiliary excretion of diclofenac.

Determination and pharmacokinetic profile of omeprazole in rat blood, brain and bile by microdialysis and high-performance liquid chromatography

The disposition and biliary excretion of omeprazole was investigated following i.v. administration to rats at 10 mg/kg. We used a microdialysis technique coupled to a validated microbore HPLC system to monitor the levels of protein-unbound omeprazole in rat blood, brain and bile, constructing the relationship of the time course of the presence of omeprazole. Microdialysis probes were simultaneously inserted into the jugular vein toward right atrium, the brain striatum and the bile duct of the male Sprague-Dawley rats for biological fluid sampling after the administration of omeprazole (10 mg/kg) through the femoral vein. The concentration-response relationship from the present method indicated linearity (r2>0.995) over a concentration range of 0.01-50 microg/ml for omeprazole. Intra-assay and inter-assay precision and accuracy of omeprazole fell well within the predefined limits of acceptability. Following omeprazole administration, the blood-to-brain coefficient of distribution was 0.15, which was calculated as the area under the concentration versus time curve (AUC) in the brain divided by the AUC in blood (k=AUCbrain/AUCblood). The blood-to-bile coefficient of distribution (k=AUCbile/AUCblood) was 0.58. The decline of unbound omeprazole in the brain striatum, blood and bile fluid suggests that there was rapid exchange and equilibration between the compartments of the peripheral and central nervous systems. In addition, the results indicated that omeprazole was able to penetrate the blood-brain barrier and undergo hepatobiliary excretion.