Microdialysis Sampling to Determine the Pharmacokinetics of Unbound SDZ ICM 567 in Blood and Brain in Awake,Freely-Moving Rats

The free concentrations of the serotoninergic 5-HT₃ antagonist SDZ ICM 567 in blood and in the central nervous system were examined in awake, freely-moving rats using blood and brain microdialysis coupled to liquid chromatography. Microdialysis probes were implanted in the jugular vein and in the frontal cortex and dialysis samples were simultaneously collected from both sites. Pharmacokinetic parameters were calculated after a 10 mg/kg intravenous dose of [¹⁴C]SDZ ICM 567. The elimination half lives measured in whole blood, brain and blood microdialysates were similar (1.7 h). The AUC_0–5h corresponding to the unbound drug was 462 ± 142 ng · ml^–1 · h in blood dialysate, not significantly different from the AUC corresponding to the free concentration in whole blood, i.e. 586 ± 63 ng · ml^–1 h. The free fraction in blood obtained in vitro by equilibrium dialysis (21%) or by microdialysis (19%) was not statistically different from that obtained in vivo (17%) in microdialysis experiments. The unbound concentrations (AUC_0–5h) of SDZ ICM 567 in the brain cortex were 86 ± 24 ng · ml^–l - h, lower than those expected from unbound blood concentrations, suggesting an active transport out of the central nervous system. Finally, microdialysis sampling allowed the determination of pharmacokinetic parameters of SDZ ICM 567 in blood and brain as well as the estimation of the free fraction of drug in blood.     

Drug Equilibration Across the Blood—Brain Barrier-Pharmacokinetic Considerations Based on the Microdialysis Method

Purpose. The purpose of the study was to investigate the influence of different rates of transport into and out of the brain, including passive and active transport, on unbound brain concentrations and profile in relation to the blood concentration profile. Special emphasis is put on hydrophilic drugs. Methods. Simulations were performed with a model including one body compartment and one brain compartment, with linear or saturable transport into and out of the brain. Comparisons were made with experimental results from microdialysis (MD) studies. Results. Three features were evident when combining the MD results: 1) equilibration across the blood-brain barrier (BBB) is rapid, 2) half-life is similar in brain and blood for most drugs, and 3) unbound brain concentrations seldom reach the level of unbound blood concentrations. A low concentration ratio brain:blood is not mainly caused by a low influx, but rather by different influx and efflux clearances. Active transport out of the brain can explain the results, but also active transport into the brain under certain conditions. A small volume of distribution in brain vs. that in the rest of the body contributes to a rapid equilibration and similar half-lives. Conclusions. Assumptions of slow equilibration of hydrophilic drugs and similar unbound concentrations across the BBB at steady state are contradicted. The results are more in line with recent findings on the presence of P-glycoprotein and other transport mechanisms at the BBB. Non-passive transport across the BBB seems to be the case for almost all drugs studies with MD so far.     

Relationship Between Enoxacin and Ciprofloxacin Plasma Concentrations and Theophylline Disposition

Certain fluoroquinolone antibiotics affect theophylline (THEO) disposition by inhibition of its metabolism, yet no studies to date have investigated the relationship between fluoroquinolone plasma concentration and THEO pharmacokinetics. The effects of two fluoroquinolones, enoxacin (ENOX) and ciprofloxacin (CIPRO), have been studied in male Sprague-Dawley rats (n = 33–46) at steady state plasma concentrations of 0–33 mg · 1^–1, achieved by supplementing an intravenous bolus dose with a constant rate infusion. The effects of steady state ENOX and CIPRO plasma concentrations on the clearance of THEO determined after an intravenous bolus dose of 6 mg · kg^–1 were described using a competitive inhibition model. The model consisted of two components, one describing a residual component of THEO clearance, which was unaffected by fluoroquinolone, the other describing the non-linear reduction of THEO clearance by fluoroquinolone. The residual clearance estimated from the model was comparable to renal clearance for THEO in the rat. The potency of each fluoroquinolone was characterised by a Ki value, the concentration reducing THEO clearance by 50% of the maximum change. These values were 4.7 µM and 16.3 µM for ENOX and CIPRO, respectively. Thus, in this study, ENOX was found to be a more potent inhibitor of THEO clearance than CIPRO. The method allowed direct in vivo comparison of potency between different fluoroquinolones, as pharmacokinetic differences, such as clearance, volume of distribution and bioavailability, were designed out.     

分光光度法测定茶碱血药浓度和唾药浓度的研究

本文对6名健康人一次静脉注射氨茶碱注射液(剂量5mg/kg),用UV法测其血药浓度的经时变化。其一定模型药物动力学参数为:t_(1/2)8.4730±2.733h;K0.08907±0.02846h~(-1);Vd0.4380±0.1809L/kg;Cmax13.2257±5.6220μg/ml。其中4名受试者唾液与血浆中茶碱浓度比率为0.5340±0.1407;7名受试者全血与血浆中茶碱浓度比率为0.7234±0.08006     

Fluconazole Distribution to the Brain: A Crossover Study in Freely-moving Rats Using In Vivo Microdialysis

Purpose. The purpose of this study was to determine if the microdialysis sampling technique is feasible to study the central nervous system distributional kinetics of a novel triazole antifungal agent, fluconazole, in an awake, freely-moving rat model, and to determine fluconazole distribution to the extracellular fluid (ECF) of the brain. Methods. The relative recovery of the microdialysis probes (CMA-12) was determined in vitro and in vivo by retrodialysis using UK-54,373, a fluorinated analog of fluconazole. Sprague-Dawley rats received 10 mg/kg and 20 mg/kg fluconazole IV bolus doses in a crossover design, and brain extracellular fluid fluconazole concentrations were monitored using microdialysis and on-line HPLC analysis. The plasma fluconazole concentration vs. time data were determined using sequential blood sampling and HPLC analysis. Results. There was no statistical difference between relative probe recoveries for both fluconazole and UK-54,373, either in vitro or in vivo, and probe recoveries did not change during the course of the in vivo crossover experiment. Fluconazole rapidly distributes into in the brain ECF and the average brain distribution coefficient (brain/plasma AUC ratio) was 0.60 ± 0.18 and was independent of dose. Plasma pharmacokinetic parameters were linear in the dose range studied. Conclusions. Fluconazole rapidly reaches a distributional equilibrium between brain extracellular fluid and plasma, and the distribution to the brain is substantial and not dependent on dose over a two-fold range. Furthermore, the results indicate that microdialysis utilizing UK-54,373 as the in vivo retrodialysis probe calibrator is a feasible method to study the transport of fluconazole into the central nervous system.     

The Design and Validation of a Novel Intravenous Microdialysis Probe: Application to Fluconazole Pharmacokinetics in the Freely-Moving Rat Model

Purpose. The purpose of this study was to design and validate a concentric, flexible intravenous microdialysis probe to determine drug concentrations in blood from the inferior vena cava of a freely-moving animal model. Methods. An intravenous microdialysis probe was constructed using fused-silica tubing and an acrylonitrile/sodium methallyl sulfonate copolymer hollow fiber. The probe was tested in vitro for the recovery of fluconazole and UK-54,373, a fluconazole analog used for probe calibration by retrodialysis. Subsequent in vivo validation was done in rats (n = 7) that had a microdialysis probe inserted into the inferior vena cava via the femoral vein, and the femoral artery was cannulated for simultaneous blood sampling. Comparisons of fluconazole pharmacokinetic parameters resulting from the two sampling methods were performed at 2 and 10 days after probe implantation. Results. There were no statistical differences between the microdialysis sampling and conventional blood sampling methods for the T_1/2, Cl, Vdss, and dose-normalized AUC by paired t-test (p > 0.05) for repeated dosing at day 2 and day 10 after probe placement. The probe recovery, as determined by retrodialysis, significantly decreased over the ten day period. This finding indicates the necessity for frequent recovery determinations during a long-term blood microdialysis experiment. Conclusions. These results show that microdialysis sampling in the inferior vena cava using this unique and robust probe design provides an accurate method of determining blood pharmacokinetics in the freely-moving rat for extended experimental periods. The probe design allows for a simple surgical placement into the inferior vena cava which results in a more stable animal preparation for long-term sampling and repeated-measures experimental designs.     

反相高效液相色谱法同时测定茶碱和3种抗癫痫药血药浓度

目的建立可同时测定茶碱和苯巴比妥、苯妥英钠、卡马西平血药浓度的反相高效液相色谱法。方法色谱柱为Promosil C18柱(150 mm×4.6 mm,5μm),流动相为甲醇-水(60∶40),检测波长205 nm,流速0.7 mL/min,柱温25℃。结果该色谱条件下,茶碱、苯巴比妥、苯妥英钠、卡马西平分离良好,血药浓度线性范围茶碱为0.30～180.00μg/mL(r=0.999 7),苯巴比妥为0.42～169.60μg/mL(r=0.999 9),苯妥英钠为0.40～170.00μg/mL(r=0.999 2),卡马西平为0.20～140.00μg/mL(r=0999 8),平均回收率分别是97.3%,98.0%,103.1%,99.3%,日内及日间精密度RSD均小于6%。结论该方法操作简便、快速、准确,4种药物互不干扰,可用于临床血药浓度监测。     

The Effect of Amiodarone on Theophylline Pharmacokinetics in the Rat

Amiodarone is an investigational antiarrhythmic agent which has been implicated in reducing the activity of the hepatic mixed-function oxidase system. To evaluate this effect further, two groups of six male Sprague–Dawley rats each received theophylline (6 mg/kg, iv) preceded by either normal saline or amiodarone HC1 (100 mg/kg, iv). Blood samples were obtained serially for a period of 6 hr and the sera were assayed for theophylline by high-pressure liquid chromatography (HPLC). In rats pretreated with amiodarone, a significant 45% reduction in the mean (± SD) systemic clearance [0.057 (0.010) vs 0.031 (0.004) liter/hr/kg, P < 0.001] and a greater than 100% increase in the mean elimination half-life [2.03 (0.46) vs 4.29 (0.71) hr, P < 0.001] of theophylline were observed. These data demonstrate an acute inhibitory effect of amiodarone on the hepatic microsomal enzyme system.     

Simultaneous Retrodialysis by Calibrator for Rapid In Vivo Recovery Determination in Target Site Microdialysis

Concentrations in the interstitial tissue space are of clinical interest for many antibiotics and can be directly measured by microdialysis. Quantitative microdialysis strongly depends on reliable recovery estimates obtained from a suitable calibrator. Cefazolin (CFZ) is frequently used as a prophylactic antibiotic to prevent surgical site infections. This study aimed to develop a reliable and rapid calibration technique for CFZ microdialysis using cefuroxime (CFR) as a calibrator, which is applied simultaneously in the opposite direction via retrodialysis. Liquid chromatography-tandem mass spectrometry method was used for the measurement of both CFZ and CFR in microdialysate. Results from in vitro microdialysis experiments confirmed that CFR does not interfere with physicochemical properties of CFZ, and the loss of CFR is proportional to the gain of CFZ in microdialysis studies. Therefore, the validated bioanalytical assay is suitable to be applied in clinical microdialysis study of CFZ where microdialysis probes are simultaneously calibrated by retrodialysis of CFR. This approach shortens the overall sampling time of in vivo microdialysis studies significantly since calibration and sampling can be performed simultaneously and not in sequence as usually done. It also eliminates the necessary washout period if probe calibration is carried out before the actual sampling time.     

双黄连对氨茶碱药动学的影响

目的 :研究双黄连对氨茶碱在人体内药动学的影响。方法 :采用高效液相色谱法测定8名健康志愿者多剂量服用双黄连口服液前、后氨茶碱的血药浓度 ,以3p97药动学软件按一室模型对数据进行处理 ,并对结果进行统计学分析。结果 :单用氨茶碱和合用双黄连后氨茶碱的Tmax 分别为 (1 66±0 56)、(1 59±0 78)h ,Cmax 分别为 (6 23±1 31)、(6 10±0 94) μg/ml ,T1/2 分别为(5 76±1 11)、(6 09±1 63)h ,CL分别为 (47 72±5 12)、(50 98±10 85)ml/(kg·h) ,Vd分别为 (369 18±40 15)、(430 37±48 33)ml/kg,AUC0→∞分别为 (84 56±14 43)、(89 27±26 35) μg/(h·ml)。结论 :双黄连明显增加氨茶碱的Vd ,对Tmax、Cmax、T1/2、CL和AUC0→∞没有影响     

甘氨酸茶碱钠缓释片与普通片药物动力学对比

采用一步液液提取反相高效液相色谱法对甘氨酸茶碱钠缓释片 (受试制剂 )与普通片 (参比制剂 )在人体内药物动力学行为进行了对比检测 ,绘制了 12名健康男性志愿受试者分别单剂量和多剂量随机交叉口服上述两种制剂后的茶碱血浆浓度 时间曲线并计算主要的药动学参数 .经统计检验 ,两种制剂的AUC无显著性差异 .单剂量和多剂量口服甘氨酸茶碱钠缓释片的相对生物利用度分别为 (91.7± 16 .8) %和 (10 7.5± 18.6 ) % .与普通片相比 ,甘氨酸茶碱钠缓释片的Cmax较低 ,而Cmin较高 ,Tmax明显滞后 ,MRT延长 ,血药浓度波动幅度显著减小 ,符合缓释制剂的特点 ,可较为安全地应用于临床 .     

人血浆中茶碱和多索茶碱的HPLC法测定

建立了HPLC法测定人血浆中的茶碱和多索茶碱.采用C_(18)色谱柱,以咖啡因为内标,甲醇-水(23:77)为流动相,检测波长273 nm.血浆经甲醇沉淀蛋白后直接进样.茶碱和多索茶碱在2.5～40μg/ml浓度范围内线性关系良好,日内、日间RSD均小于5.2%.     

Pharmacokinetics of Terbutaline and Theophylline in Guinea Pigs when Administered Simultaneously

Abstract: Simultaneous administration of terbutaline and theophylline to guinea pigs did not cause significant alterations of the pharmacokinetic properties of any of the drugs. Terbutaline sulphate 24 μg kg^?1 and aminophylline 52 mg kg^?1 (7.42.10^?8 and 2.37.10^?4 mol kg^?1 respectively) were given by a bolus intravenous injection, producing plasma concentrations in the range 0–15 ng terbutaline sulphate per ml (0–46 nanomol 1^?1) and 10–85μg theophylline per ml (50–429 μmol 1^?1). Pharmacokinetic analyses of time courses of plasma concentrations of intact drugs and investigations of tissue distribution 1 hour after the administration were performed. The results showed a weak, statistically insignificant trend of the peripheral compartment of the 2-compartment model to sequester a larger fraction of the drugs when these were administered simultaneously.     

Distribution of Tacrine Across the Blood–Brain Barrier in Awake,Freely Moving Rats Using in Vivo Microdialysis Sampling

Microdialysis was used to sample simultaneously the distribution of THA (9-amino-l,2,3,4-tetrahydroacridine; Tacrine), a potential anti-Alzheimer agent, both in blood and across the blood–brain barrier of anesthetized and awake, freely moving rats. Microdialysis probes were implanted in the jugular vein and dorsal hippocampus and dialysis samples were simultaneously collected from both sites. Dialysis samples were analyzed using a microbore column chromato-graphic assay with a detection limit of 0.3 ng/ml. Pharmacokinetic parameters were calculated after a 1 mg/kg intravenous dose of THA. Plasma pharmacokinetics followed a biexponential mode, with t _1/2(dis.) = 8.4 ± 2.7 min and t _1/2(elim.) = 76.7 ± 24.2 min for awake, freely moving rats. THA rapidly penetrated the blood–brain barrier, with maximum concentrations attained within 60 min post-dose. In the brain of awake, freely moving rats t _1/2(abs.) was 26.0 ± 5.2 min and t _1/2(elim.) was 99.1 ± 17.7 min. THA levels in hippocampus extracellular fluid were 10 times lower than those in plasma. For anesthetized rats, the t _l/2(elim.) in blood was 154.8 ± 46.8 min, while in the hippocampus t _1/2(elim.) was 159.5 ± 31.7 min. The binding of THA in rat plasma was 56.2 ± 5.0%, while the fraction bound to rat whole blood was 73.3 ± 4.1% as determined by microdialysis and ultrafiltration.     

Blood-Brain Barrier Equilibration of Codeine in Rats Studied with Microdialysis

Purpose. The purpose of the study was to investigate the distribution of codeine across the blood-brain barrier (BBB) in rats by micro-dialysis (MD). Methods. Rats were administered intravenous infusion of codeine in doses of (1) 10 mg/kg, (2) 20 mg/kg for 10 min, and (3) an exponential infusion for 2 h aiming at a plasma concentration of 2500 ng/ml, in a crossover design (n = 6). Microdialysis was used to determine codeine unbound concentrations in blood and brain extracellular fluid (ECF). Total brain tissue and plasma concentrations were also determined. Nalorphine was used as a calibrator for measurement of in vivo recovery. Results. Relative recovery and retrodialysis loss of codeine and nalorphine were similar both in vitro and in vivo. Codeine was rapidly transported into the brain ECF with identical influx and efflux clearance across the BBB. The AUC ratios of brain to blood were 0.99 ± 0.25 and 0.95 ± 0.16 for Dose 1 and 2, respectively. The C_ss ratio of brain to blood was 1.06 ± 0.12 for the exponential infusion. The half-lives were 25 ± 4 min, 22 ± 2 min in blood and 27 ± 5 min, 25 ± 5 min in brain for Dose 1 and Dose 2, respectively. Total brain tissue concentrations were 3.6 ± 1.2-fold higher than the unbound concentrations in brain. Codeine was demethylated to morphine with an unbound AUC_{bIood,morphine}/AUC_{blood,codeine} ratio of 7.7 ± 5.1% in blood. No morphine was detected in brain MD, but total concentrations were possible to measure. Conclusions. Codeine rapidly reached a distributional equilibrium with equal unbound concentrations in blood and brain. The brain transport of codeine did not show any dose-dependency.     

茶碱麻黄碱片的HPLC测定

建立了高效液相色谱法同时测定茶碱麻黄碱片中茶碱和盐酸麻黄碱的含量.采用C18柱,以0.06mol/L磷酸二氢钠溶液-甲醇(80:20)为流动相,检测波长210nm.两者分别在25～200、5.8～46.4μg/ml范围内线性关系良好,平均回收率分别为100.5%、100.6%.     

高效液相色谱法和化学发光酶免疫分析法测定茶碱的血药浓度

目的采用高效液相色谱法和化学发光酶免疫分析法对茶碱血药浓度进行测定,比较两种方法的差异。方法分别使用高效液相色谱法和化学发光酶免疫分析法对40例患者使用茶碱后的血药浓度进行检测,对两种方法的结果进行比较。结果高效液相色谱法的平均回收率为102.77%,日内RSD为0.8543%～7.5472%,日间RSD为1.4758%～4.6979%;化学发光酶免疫分析法的平均回收率为101.17%,日内RSD为2.2554%～7.4972%,日间RSD为0.789 8%～4.391 7%。结论两种方法的茶碱浓度测定值无显著性差异,测定结果无需互相校正。     

微透析法测定虎杖苷的体外血浆蛋白结合率及与超滤法的比较

目的 采用微透析技术研究虎杖苷的体外血浆蛋白结合率,并与超滤法比较。方法 微透析探针依次浸入含虎杖苷20,60,200μg·mL1的大鼠、人血浆中,灌注器以2.5μg·min1的流速依次灌注含虎杖苷0,10,30,100,300μg·mL1的生理盐水,每15min收集1次样品,HPLC分析虎杖苷浓度。以灌注液与透析液中虎杖苷的浓度差对灌注液浓度进行线性回归,计算血浆中游离虎杖苷的浓度,进而计算虎杖苷的血浆蛋白结合率,并与超滤法进行比较。结果 微透析测定虎杖苷与大鼠、人血浆蛋白结合率平均值分别为86.15%,89.08%,超滤法分别为85.60%和87.24%,两种方法结果比较接近。结论 虎杖苷与大鼠、人血浆蛋白有较高的结合率,微透析法和超滤法结果一致。     

茶碱在正常及肝纤维化大鼠体内的药物动力学

目的比较茶碱在正常及肝纤维化大鼠体内的药物动力学。方法 SD大鼠24只,分成4组:静脉给药正常组、静脉给药模型组、口服给药正常组和口服给药模型组,每组各6只,采用尾静脉注射或灌胃方式给予茶碱5mg/kg,用HPLC法测定茶碱血药浓度,运用DAS2.1.1拟合药动学参数,并采用SPSS13.0软件进行统计分析。结果在口服和静脉给药条件下,茶碱的药动学参数AUC0-24h、AUC0-∞、CLz(或CLz/F)、MRT0-24h、MRT0-∞和t1/2z在正常鼠和肝纤维化鼠之间差异有统计学意义(P<0.05),Cmax,tmax,Vz(或Vz/F)的差异则无统计学意义。结论茶碱在大鼠体内的药动学会受肝纤维化显著影响。     

Application of Microdialysis in Pharmacokinetic Studies

The objective of this review is to survey the recent literature regarding the various applications of microdialysis in pharmacokinetics. Microdialysis is a relatively new technique for sampling tissue extracellular fluid that is gaining popularity in pharmacokinetic and pharmacodynamic studies, both in experimental animals and humans. The first part of this review discusses various aspects of the technique with regard to its use in pharmacokinetic studies, such as: quantitation of the microdialysis probe relative recovery, interfacing the sampling technique with analytical instrumentation, and consideration of repeated procedures using the microdialysis probe. The remainder of the review is devoted to a survey of the recent literature concerning pharmacokinetic studies that apply the microdialysis sampling technique. While the majority of the pharmacokinetic studies that have utilized microdialysis have been done in the central nervous system, a growing number of applications are being found in a variety of peripheral tissue types, e.g. skin, muscle, adipose, eye, lung, liver, and blood, and these are considered as well. Given the rising interest in this technique, and the ongoing attempts to adapt it to pharmacokinetic studies, it is clear that microdialysis sampling will have an important place in studying drug disposition and metabolism.