Tzung-Jiun Tsai

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 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.

Determination of chlorogenic acid in rat blood by microdialysis coupled with microbore liquid chromatography and its application to pharmacokinetic studies.

To investigate the pharmacokinetics of unbound chlorogenic acid, a sensitive microbore liquid chromatographic method for the determination of chlorogenic acid in rat blood by microdialysis has been developed. A microdialysis probe was inserted into the jugular vein of male Sprague-Dawley rats, to which chlorogenic acid (20, 40, 60 or 80 mg/kg, i.v.) had been administered. On-line microdialysate was directly injected into a microbore column using a methanol-100 mM sodium dihydrogenphosphate (30:70, v/v, pH 2.5 adjusted with orthophosphoric acid) as the mobile phase and ultraviolet detection at 325 nm. The method is rapid, easily reproduced, selective and sensitive. The limit of detection for chlorogenic acid was 0.01 microg/ml and the limit of quantification was 0.05 microg/ml. The in vivo recovery of the chlorogenic acid of the microdialysis probe, based on a 5 microg/ml standard, was approximately 49-65% (n=6). The disposition of chlorogenic acid at each dose was best fitted to a two-compartment pharmacokinetic model. The area under the concentration curve increased greater than in direct proportion with the dose and terminal disposition become much slower as the dose was increased. The results indicated that the pharmacokinetics of unbound chlorogenic acid in rat blood is non-linear.

Measurement and pharmacokinetics of unbound 20(S)-camptothecin in rat blood and brain by microdialysis coupled to microbore liquid chromatography with fluorescence detection.

To characterize the pharmacokinetics of protein-free camptothecin in blood and brain we implanted microdialysis probes into the jugular vein and striatum of rats for unbound drug sampling and determination. Camptothecin (2 or 5 mg/kg, i.v., n=6) was then administered from the femoral vein, and microdialysates were collected from blood and brain of both sites and assayed by a validated microbore scale high-performance liquid chromatographic method. The mobile phase consisted of methanol-100 mM monosodium phosphoric acid (35:65, v/v, pH 2.5) with a flow-rate 0.05 ml/min. The fluorescence response for camptothecin was observed at excitation and emission wavelengths of 360 and 440 nm, respectively. Pharmacokinetic parameters were calculated from the corrected data for dialysate concentrations of camptothecin versus time. The results suggest that the pharmacokinetics of unbound camptothecin in blood and brain can be fitted best to a two- and one-compartment model, respectively. Camptothecin rapidly entered the extracellular fluid of brain striatum at 10 min following camptothecin administration.

Measurement of hydroxyl radical in rat blood vessel by microbore liquid chromatography and electrochemical detection: an on-line microdialysis study

Salicylic acid (0.5 mM) is used as a trapping reagent of hydroxyl radical, and the formed 2,3- and 2,5-dihydroxybenzoic acids were collected via an on-line microdialysis device from the blood vessels. This study revealed the use of a sensitive liquid chromatographic system with electrochemical detection for the determination of 2,3- and 2,5-dihydroxybenzoic acids. Mobile phase consisted of 0.1 M monochloroacetic acid, 10 mM EDTA, 0.5 mM sodium octylsulfate, 20% acetonitrile and 5% tetrahydrofuran in 1 l (pH 3.0 adjusted with 1 M NaOH), and the flow-rate of 0.05 ml/min were found to be optimum. Isocratic separation of these adducts on a microbore column (reversed-phase C18, 150x1 mm I.D., 5 microm) was achieved within 10 min. The optimal applied potential of dihydroxybenzoic acids was set at 750 mV based on a hydrodynamic study. This method has the detection limits of 1.3 pmol/ml (or 0.2 ng/ml) for 2,3- and 2,5-dihydroxybenzoic acids in Ringer solution (at signal-to-noise ratio=3).

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.

Simultaneous measurement of cefuroxime in rat blood and brain by microdialysis and microbore liquid chromatography: Application to pharmacokinetics

To characterize the pharmacokinetics of cefuroxime in rat blood and brain, microdialysis probes were inserted into the jugular vein and brain striatum, respectively. Cefuroxime (20 mg/kg, i.v.) was administered via the femoral vein. Blood microdialysates were automatic injected onto microbore liquid chromatography via an on-line injectors. The mobile phase consisted of methanol-100 mM monosodium phosphoric acid (25:75, v/v, pH 5.0) with a flow-rate of 0.05 ml/min. Ultraviolet detector was set at a wavelength of 280 nm for cefuroxime. The present assay enhanced the detection sensitivity and enabled the determination of cefuroxime down to 5 ng/ml. The pharmacokinetic data demonstrated that the area under the concentration curve (AUC) ratio of unbound cefuroxime in rat brain and blood was about 4.2% after cefuroxime (20 mg/kg, i.v.) administration. These results provided further evidence that cefuroxime could penetrate the blood-brain barrier.

The compliance of doctors with viral hepatitis B screening and antiviral prophylaxis in cancer patients receiving cytotoxic chemotherapy using a hospital-based screening reminder system.

Background and Aim Screenings for hepatitis B surface antigen (HBsAg) and antiviral prophylaxis are recommended for HBsAg-positive patients before the start of cytotoxic chemotherapy; however, compliance with these recommendations varies among doctors. We investigated the compliance of doctors with these recommendations using a reminder system and assessed the outcomes of HBsAg-positive patients receiving cytotoxic chemotherapy. Methods Using a computer-assisted reminder system, doctors were alerted of both HBsAg screening and antiviral prophylaxis prior to prescribing chemotherapy. The compliance between different doctors and outcomes of patients were investigated during the period of execution of this system. The rates of compliance with both recommendations were compared among various cancer types. Results A total of 1053 patients were enrolled, of which only 88 had previous data pertaining to HBsAg status. Using this reminder system, an overall screening rate of 85.5% (825/965) was achieved and did not significantly differ according to cancer type. However, the overall antiviral prophylactic rate was only 45.5% (61/134). The rates of antiviral prophylaxis were lower for doctors treating lung, breast and colorectal cancers than for those treating hematological malignancies (all p<0.05). Consequently, the rate of HBV reactivation was lower in patients who received antiviral prophylaxis than in those who did not (1.6% vs. 15.1%; p<0.01). Multivariate analysis revealed that male gender and antiviral prophylaxis were both related to reactivation of hepatitis B (p<0.05). Conclusions By using this reminder system, the overall screening rate for HBsAg was satisfactory, whereas the antiviral prophylaxis was inadequate in patients with solid tumors due to the varying compliance of the attending doctors. Further strategies to improve both screening and prophylaxis are needed to minimize HBV-related events during cytotoxic chemotherapy.

Reappraisal of endoscopic papillary balloon dilation for the management of common bile duct stones

Although endoscopic sphincterotomy (EST) is still considered as a gold standard treatment for common bile duct (CBD) stones in western guideline, endoscopic papillary balloon dilation (EPBD) is commonly used by the endoscopists in Asia as the first-line treatment for CBD stones. Besides the advantages of a technical easy procedure, endoscopic papillary large balloon dilation (EPLBD) can facilitate the removal of large CBD stones. The indication of EPBD is now extended from removal of the small stones by using traditional balloon, to removal of large stones and avoidance of lithotripsy by using large balloon alone or after EST. According to the reports of antegrade papillary balloon dilatation, balloon dilation itself is not the cause of pancreatitis. On the contrary, adequate dilation of papillary orifice can reduce the trauma to the papilla and pancreas by the basket or lithotripter during the procedure of stone extraction. EPLBD alone is as effective as EPLBD with limited EST. Longer ballooning time may be beneficial in EPLBD alone to achieve adequate loosening of papillary orifice. The longer ballooning time does not increase the risk of pancreatitis but may reduce the bleeding episodes in patients with coagulopathy. Slowly inflation of the balloon, but not exceed the diameter of bile duct and tolerance of the patients are important to prevent the complication of perforation. EPBLD alone or with EST are not the sphincter preserved procedures, regular follow up is necessary for early detection and management of CBD stones recurrence.

Upper gastrointestinal lesions in patients receiving clopidogrel anti-platelet therapy

BACKGROUND/PURPOSE Clopidogrel is associated with a high incidence of upper gastrointestinal bleeding in high-risk patients. However, the characteristic upper gastrointestinal lesions in symptomatic clopidogrel users remain unclear. The aims of this study were to investigate the characteristics of endoscopic findings in clopidogrel users undergoing endoscopy for upper gastrointestinal symptoms and to compare the clinical characteristics and upper gastrointestinal lesions between symptomatic clopidogrel and aspirin users. METHODS This observational study included 215 consecutive patients receiving clopidogrel (n=106) or low-dose aspirin (n=109) therapy who underwent endoscopy for dyspeptic symptoms. The upper gastrointestinal lesions were carefully assessed, and a complete medical history was obtained by a standard questionnaire. RESULTS The frequencies of hemorrhagic spots, erosions and peptic ulcers in the symptomatic clopidogrel users were 25%, 39% and 39%, respectively. Among the peptic ulcer patients on clopidogrel therapy, the distributions of ulcers were 78%, 5% and 17% in the stomach, duodenum and both, respectively. Compared with the aspirin group, the clopidogrel group was older and had higher frequencies of past ulcer history and past gastrointestinal bleeding history in their clinical characteristics. By contrast, the clopidogrel users had a lower prevalence of active Helicobacter pylori infection than aspirin users (17% vs. 35%, respectively, p=0.007). Regarding to the endoscopic findings, the clopidogrel users had higher frequencies of hemorrhagic spots (25% vs. 10%) and peptic ulcer (39% vs. 24%) than aspirin users (p=0.004 and 0.027, respectively). CONCLUSION Most peptic ulcers in clopidogrel users are located in the stomach. The frequencies of hemorrhagic spots and peptic ulcers in symptomatic clopidogrel users are higher than those in symptomatic aspirin users.