Determination of unbound 20(S)-camptothecin in rat bile by on-line microdialysis coupled to microbore liquid chromatography with fluorescence detection

Recent trends in microdialysis sampling integrated with conventional and microanalytical systems for monitoring biological events: a review

Microdialysis (MD) is a sampling technique that can be employed to monitor biological events both in vivo and in vitro. When it is coupled to an analytical system, microdialysis can provide near real-time information on the time-dependent concentration changes of analytes in the extracellular space or other aqueous environments. Online systems for the analysis of microdialysis samples enable fast, selective and sensitive analysis while preserving the temporal information. Analytical methods employed for online analysis include liquid chromatography (LC), capillary (CE) and microchip electrophoresis and flow-through biosensor devices. This review article provides an overview of microdialysis sampling and online analysis systems with emphasis on in vivo analysis. Factors that affect the frequency of analysis and, hence, the temporal resolution of these systems are also discussed.

Determination of camptothecin and 10-hydroxycamptothecin in human plasma using polymer monolithic in-tube solid phase microextraction combined with high-performance liquid chromatography

A biocompatible in-tube solid-phase microextraction (SPME) device was used for the direct and on-line extraction of camptothecin and 10-hydroxycamptothecin in human plasma. Biocompatibility was achieved through the use of a poly(methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary column for extraction. Coupled to high performance liquid chromatography (HPLC) with UV detection, this on-line in-tube SPME method was successfully applied to the simultaneous determination of camptothecin and 10-hydroxycamptothecin in human plasma. The calculated detection limits for camptothecin and 10-hydroxycamptothecin were found to be 2.62 and 1.79 ng/mL, respectively. The method was linear over the range of 10-1000 ng/mL. Excellent method reproducibility was achieved, yielding RSDs of 2.49 and 1.59%, respectively. The detection limit (S/N = 3) of camptothecin was found to reach 0.1 ng/mL using fluorescence detection. The proposed method was shown to cope robustly with the extraction and analysis of camptothecin and 10-hydroxycamptothecin in plasma samples.

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.

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 and pharmacokinetic study of meropenem in rat bile using on-line microdialysis and liquid chromatography

Meropenem is a carbapenem antibiotic with a wide spectrum of activity against both Gram-positive and Gram-negative bacteria. Because of its clinical efficacy, meropenem is an excellent choice for the treatment of serious infections in both adults and children. The knowledge of tissue concentrations of antibiotic in an infection site is valuable for the prediction of treatment outcome. To investigate the biliary disposition of meropenem, we utilized a minimally invasive sampling technique with a shunt linear microdialysis probe for continuous sampling in the biliary excretion studies. Analysis of meropenem in the dialysates was achieved using a LiChrosorb RP-18 column (Merck, 250 x 4.6 mm I.D.; particle size 5 microm) maintained at ambient temperature. The mobile phase was 50 mM monosodium phosphoric acid-methanol (80:20, v/v, pH 3.0). The UV detector wavelength was set at 298 nm. The area under the concentration-time curve and elimination half-lives of meropenem were about 6144 +/- 1494 min microg/ml and 61 +/- 17 min, respectively. This study represents a successful application of the microdialysis technique, which is an effective method for pharmacokinetic and biliary drug excretion studies.

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.

Separation methods for camptothecin and related compounds

This paper reviews working procedures for the analytical determination of camptothecin and analogues. We give an overview of aspects such as the chemistry, structure-activity relationships, stability and mechanism of action of these antitumor compounds. The main body of the review describes separation techniques. Sample treatment and factors influencing high-performance liquid chromatography development are delineated. Published high-performance liquid chromatographic methods are summarized to demonstrate the variability and versatility of separation techniques and a critical evaluation of separation efficiency, detection sensitivity and specificity of these methods is reported.

Quantitation of camptothecin and related compounds

Camptothecin and congeners represent a clinically very useful class of anticancer agents. Proper identification and quantitation of the original compounds and their metabolites in biological fluids is fundamental to assess drug metabolism and distribution in animals and in man. In this paper we will review the recent literature available on the methods used for separation and quantitative determination of the camptothecin family of drugs. Complications arise from the fact that they are chemically labile, and the pharmacologically active lactone structure can undergo ring opening at physiological conditions. In addition, a number of metabolic changes usually occur, producing a variety of active or inactive metabolites. Hence, the conditions of extraction, pre-treatment and quantitative analysis are to be carefully calibrated in order to provide meaningful results.

Analytical approaches for traditional chinese medicines exhibiting antineoplastic activity

Traditional Chinese medicines have attracted great interest in recent researchers as alternative antineoplastic therapies. This review focuses on analytical approaches to various aspects of the antineoplastic ingredients of traditional Chinese medicines. Emphasis will be put on the processes of biological sample extraction, separation, clean-up steps and the detection. The problems of the extraction solvent selection and different types of column chromatography are also discussed. The instruments considered are gas chromatography, capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) connected with various detectors (ultraviolet, fluorescence, electrochemistry, mass, etc.). In addition, determinations of antineoplastic herbal ingredients, including camptothecin, taxol (paclitaxel), vinblastine. vincristine, podophyllotoxin, colchicine, and their related compounds, such as irinotecan, SN-38, topotecan, 9-aminocamptothecin, docetaxel (taxotere) and etoposide, are briefly summarized. These drugs are structurally based on the herbal ingredients, and some of them are in trials for clinical use. Evaluation of potential antineoplastic herbal ingredients, such as harringtonine, berberine, emodin, genistein, berbamine, daphnoretin, and irisquinone, are currently investigated in laboratories. Other folk medicines are excluded from this paper because their antineoplastic ingredients are unknown.

Effect of P-glycoprotein modulators on the pharmacokinetics of camptothecin using microdialysis

1. By performing microdialysis, this study investigated the pharmacokinetics of unbound camptothecin in rat blood, brain and bile in the presence of P-glycoprotein mediated transport modulators (cyclosporin A, berberine, quercetin, naringin and naringenin). Pharmacokinetic parameters of camptothecin were assessed using a non-compartmental model. 2. Camptothecin rapidly crosses the blood-brain barrier (BBB) within 20 min after camptothecin administration. The disposition of camptothecin in rat bile appeared to have a slow elimination phase and a peak concentration after 20 min of camptothecin administration. The area under the concentration versus time curve (AUC) for camptothecin in bile significantly surpassed that in blood, suggesting active transport of hepatobiliary excretion. 3. In the presence of cyclosporin A camptothecin AUC, in the brain, was significantly elevated but no significant change in the presence of berberine, quercetin, naringin and naringenin. 4. With treatment by smaller doses of quercetin (0.1 mg x kg(-1)), naringin (10 mg x kg(-1)) and naringenin (10 mg x kg(-1)), they significantly diminished the camptothecin AUC in bile, but was not altered by the treatment of berberine (20 mg x kg(-1)), a higher dose of quercetin (10 mg x kg(-1)), and cyclosporin A treated (20 mg x kg(-1)) and pretreated groups. 5. The distribution ratio (AUC(bile)/AUC(blood)) of camptothecin in bile was decreased in the cyclosporin A, quercetin, naringin and naringenin treated groups. However, the distribution ratio in the brain was increased in the cyclosporin A groups, but was decreased in the groups treated with quercetin, naringin and naringenin. These results revealed that P-glycoprotein might modulate hepatobiliary excretion and BBB penetration of camptothecin.

Simultaneous determination of unbound ropivacaine in rat blood and brain using microdialysis

To investigate the pharmacokinetics of ropivacaine in rat blood and brain, a sensitive HPLC method and microdialysis were developed for the simultaneous determination of unbound ropivacaine in rat blood and brain. Adult, male Sprague-Dawley rats (290-350 g) were anesthetized with sodium pentobarbital (50 mg/kg, i.p.). Two microdialysis probes were inserted, one into the jugular vein toward right atrium, and one into the brain striatum of rats. Ropivacaine (5 mg/kg, i.v.) was then administered via the femoral vein. Blood and brain dialysates were collected and eluted with a mobile phase containing methanol-acetonitrite-20 mM monosodium phosphoric acid (pH 5.5) (10:40:50, v/v/v) in a liquid chromatographic system. Separation of ropivacaine was achieved by a CN column (Phenomenex Luna, 250x4.6 mm, particle size 5 microm; Torrance, CA, USA) within 10 min. The UV detector wavelength was set at 205 nm and the detection limit of ropivacaine was 20 ng/ml. The intra- and inter-day accuracy and precision of the analyses were less than 10% in the ranges of 0.02-5 microg/ml. The pharmacokinetic data were calculated from the individual animal measurements of dialysate concentration versus time. This method exhibits no endogenous interference and its sensitivity is sufficient for the determination of biological samples. The present results confirm that microdialysis sampling followed by LC separation with UV detection represents a viable approach for the measurement of free ropivacaine in rat brain and plasma.

Determination and pharmacokinetic study of unbound cefepime in rat bile by liquid chromatography with on-line microdialysis

Biliary excretion and intestinal reabsorption in enterohepatic circulation play major dispositional roles for some drugs. To investigate biliary excretion of drug, we inserted a microdialysis probe into the bile common duct of rat between the liver and the duodenum. In order to avoid the obstruction of bile fluid or bile salt waste, a shunt linear microdialysis probe was used for simultaneous and continuous sampling following intravenous administration of cefepime (50 mg/kg, i.v.). Separation and quantitation of cefepime in the dialysates were achieved using a LiChrosorb RP-18 column (Merck; 250x4.6 mm I.D., particle size 5 microm) maintained at ambient temperature. Samples were eluted with a mobile phase containing 100 mM monosodium phosphoric acid (pH 3.0)-methanol (87:13, v/v). The UV detector wavelength was set at 270 nm. The result indicates that the elimination half-life of cefepime in bile was 64.01+/-9.32 min. This study also served as an example for the microdialysis application in the biliary excretion study of drug.

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

1. In vivo microdialysis with HPLC was used to investigate the pharmacokinetics of pefloxacin and its interaction with cyclosporin A. Microdialysis probes were inserted into the jugular vein/right atrium, the striatum and the bile duct of male Sprague-Dawley rats. Biological fluid sampling thereby allowed the simultaneous determination of pefloxacin levels in blood, brain and bile. 2. Following pefloxacin administration, the brain-to-blood coefficient of distribution was 0.036. This was calculated by dividing the area under the concentration curve (AUC) of pefloxacin in brain by its AUC in blood (k=AUC(brain)/AUC(blood)). 3. When the P-glycoprotein cyclosporin A (10 mg kg(-1)) was co-administered with pefloxacin (10 mg kg(-1)), the AUC and the mean residence time in rat blood did not differ significantly (P>0.05). Similarly, the pharmacokinetics of pefloxacin in rat brain was not affected by the presence of cyclosporin A. 4. The AUC of unbound pefloxacin in bile was significantly greater than that in blood. The disposition of pefloxacin in rat bile shows a slow elimination phase following a peak concentration 30 min after pefloxacin administration (10 mg kg(-1), i.v.). The bile-to-blood coefficient of distribution (k=AUC(bile)/AUC(blood)) was 1.53. 5. The results indicated that pefloxacin was able to penetrate the blood-brain barrier and that the concentration in bile was greater than that in the blood, suggesting active biliary excretion of pefloxacin. Current data obtained from rats show no significant impact of cyclosporin A on the pharmacokinetics of pefloxacin in rat blood and brain when administered by concomitant i.v. bolus.

Measurement and pharmacokinetic analysis of unbound ceftazidime in rat blood using microdialysis and microbore liquid chromatography

To evaluate the biodisposition of ceftazidime in rat blood, a rapid and simple microbore liquid chromatographic technique together with a microdialysis sampling technique were developed. This method involves an on-line design for blood dialysate directly injected into a microbore liquid chromatographic system. The chromatographic conditions consisted of a mobile phase of methanol-acetonitrile-100 mM monosodium phosphoric acid (pH 3.0) (10:10:80, v/v/v) pumped through a microbore reversed-phase column at a flow-rate of 0.05 ml/min. With the detection wavelength set at 254 nm, a good linear correlation was observed between the peak area and the ceftazidime concentration at 0.1 to 50 microg/ml (r=0.999). Microdialysis probes, being custom-made, were screened for acceptable in vivo recovery while chromatographic resolution and detection were validated for response linearity, as well as intra-day and inter-day variabilities. This method was then applied to the pharmacokinetic profiling of ceftazidime in blood following intravenous 50 mg/kg administration to rats. The pharmacokinetics was calculated from the corrected data for dialysate concentrations of ceftazidime versus time. This method has been used to study ceftazidime pharmacokinetics in rats and has proven to be rapid and reproducible.