抗生素活性时程的评估指标:靶组织游离药物的浓度

评价抗生素临床疗效的常用参数包括:最低抑菌浓度(MIC)、抗生素后效应(PAE)以及一些基于MIC的药动学/药效学参数,如t>MIC,cmax/MIC,AUC/MIC等。但由于抗生素的蛋白质结合率不同、组织分布不均匀和各种屏障等因素的影响,上述参数都存在一定的局限性。靶组织游离药物浓度是一个重要的药动学/药效学模型参数,能够更好地说明抗生素的临床疗效。近年来,国内外报道的研究靶点药物分布的方法有很多,其常用方法是利用皮肤水疱研究、成像技术和透析技术测定抗生素在靶组织的分布浓度。总之,新技术的介入提供了更多的靶点药物分布的信息。     

Determination of norfloxacin free interstitial levels in skeletal muscle by microdialysis

Tissue penetration and distribution of antibiotics are important issues when establishing antibiotic therapies. Free concentrations of antibiotics at the infection site are responsible for bacteria killing effect. The knowledge of the correlation between blood levels and tissue concentrations can be helpful for adequate dosing of these drugs. It was the aim of this study to investigate norfloxacin pharmacokinetics in rats to predict free interstitial levels of the drug, determined by microdialysis, using pharmacokinetic parameters derived from total plasma data. Norfloxacin free tissue and total plasma levels were determined in Wistar rats after administering 5 and 10 mg/kg i.v. bolus doses. Plasma and microdialysis samples were analyzed by high-performance liquid chromatography. Norfloxacin plasma pharmacokinetics was consistent with a two compartments model. A simultaneous fitting of plasma and tissue concentrations was performed using a proportionality factor because norfloxacin free tissue levels determined by microdialysis were lower than those predicted using plasma data. A similar proportionality (f(T)) factor was calculated by the computer program Scientist((R)) for both doses (0.25 +/- 0.08). It can be concluded that it is possible to predict concentration time profiles of norfloxacin in the peripheral compartment based on plasma data using the adequate tissue penetration factor.     

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.     

Tissue penetration of cefpodoxime and cefixime in healthy subjects

Microdialysis is a technique that allows the measurement of free antibiotic concentrations in different tissues, which are responsible for the antibacterial activity at the infection site. In an open, randomized, 2-way crossover study in healthy volunteers, the muscle penetration of orally administered cefpodoxime (400 mg) and cefixime (400 mg) was compared using microdialysis. The results show that the total plasma concentration-time profiles of each antibiotic were similar; the area under the curve for cefpodoxime was 22.4 +/- 8.7 versus 25.6 +/- 8.5 mg/L*h for cefixime. However, tissue penetration was twice as high for cefpodoxime (area under the curve 15.4 +/- 5.1 mg/L*h) as for cefixime (area under the curve 7.3 mg/L*h). This degree of tissue distribution is consistent with their protein binding of 21% for cefpodoxime and 65% for cefixime. After equilibration, the unbound tissue concentrations of both antibiotics were similar to their unbound plasma concentrations. Pharmacokinetic modeling was applied to describe the pharmacokinetic profiles in plasma and muscle. The study demonstrates that cefpodoxime shows greater tissue penetration than cefixime.     

A novel way to investigate the effects of plasma exchange on antibiotic levels: use of microdialysis

Plasma exchange (PE) is a treatment modality frequently used for many autoimmune diseases and may cause extracorporeal elimination of antibiotics. No data currently exist on antibiotic concentrations in extracellular fluid during PE. The aim of this study is to describe the effect of PE on the serum and subcutaneous tissue pharmacokinetics of piperacillin administered as a continuous infusion in a critically ill 17-year-old patient with Guillain-Barré syndrome and ventilator-associated pneumonia on Days 1 and 4 of antibiotic therapy. The effect of PE on piperacillin concentrations appears to be small. On Day 1, an estimated 7% of total piperacillin eliminated during PE was attributable to PE. On Day 4 this was estimated to be 11%. Using the in vivo sampling technique microdialysis, we have been able to show that a small redistribution of piperacillin from tissue to serum occurs in response to the reducing serum concentrations caused by PE. In critically ill patients, we believe that administration of a beta-lactam antibiotic by continuous infusion should be considered to maintain serum and tissue concentrations of these time-dependent antibiotics.     

Interpretation of pharmacologic data in respiratory tract infections

Few serum pharmacokinetic parameters of antibiotics are predictors of tissue distribution and, for instance, more useful are studies of tissue concentrations in the respiratory tree. Significant antibiotic concentrations can be obtained at various sites of potential infection: lung parenchyma; alveolar macrophages; and bronchial mucosa and secretions. New models using broncho-alveolar lavage allow studies of antibiotic concentrations in epithelial lining fluid that are good predictors of antibiotic activity in lung infections. In studies in human respiratory tissues for superinfected bronchitis, concentrations of macrolides, quinolones or beta-lactans in bronchial secretions, or mucosa, correlated with satisfactory clinical response, and eradication of pathogens. Pulmonary kinetics of aminoglycosides or beta-lactams have been studied using a canine model. Also in murine models of pneumonia, pharmacokinetic parameters have been determined for quinolones and newer macrolides.     

Penetration of piperacillin and tazobactam into pneumonic human lung tissue measured by in vivo microdialysis

OBJECTIVES: The pharmacokinetic profile of antibiotics at the site of anti-infective action is one of the most important determinants of drug response, since it correlates with antimicrobial effect. Up to now, only limited information on the lung tissue pharmacokinetics of antibiotic agents has been available. The aim of this study was to measure, using a new microdialysis-based approach, antibiotic penetration into the extracellular space fluid of pneumonic human lung parenchyma. PATIENTS AND METHODS: The lung penetration of a combination of piperacillin and tazobactam, substances with low protein binding, was determined in five patients suffering from pneumonia and metapneumonic pleural empyema. The condition was treated by decortication after lateral thoracotomy. Intra-, or post-operatively, respectively, two microdialysis probes were inserted into pneumonic lung tissue, and into healthy skeletal muscle to obtain reference values. Serum and microdialysis samples were collected at 20-min intervals for at last 8 h following i.v. administration of a single dose of 4 g piperacillin and 500 mg tazobactam. RESULTS: The mean free interstitial concentration profiles of piperacillin in infected lung tissue and serum showed a maximal tissue concentration (Cmax) of 176.0 +/- 105.0 mg l-1 and 326.0 +/- 60.6 mg l-1, respectively. The mean AUC (area under the curve) for infected lung tissue was 288.0 +/- 167.0 mg.h l-1 and for serum 470.0 +/- 142.0 mg.h l-1. There was a statistically significant difference between AUC (lung) and AUC (serum) (P = 0.018) as well as between AUC (lung) and AUC (muscle) (P = 0.043). The intrapulmonary concentrations of piperacillin and tazobactam exceeded the minimum inhibitory concentrations (MIC) for most relevant bacteria for 4-6 h. The procedure was well tolerated by all patients and no adverse events or microdialysis-associated side-effects were observed. CONCLUSION: This microdialysis technique enabled continuous tissue pharmacokinetic measurement of free, unbound anti-infective agents in the lung tissue of patients with pneumonia. The present data corroborate the use of piperacillin and tazobactam in the treatment of lung infections caused by extracellular bacteria and demonstrate the distribution of piperacillin and tazobactam in the interstitial space of pneumonic lung tissue.     

Microdialysis as an Important Technique in Systems Pharmacology—a Historical and Methodological Review

Microdialysis has contributed with very important knowledge to the understanding of target-specific concentrations and their relationship to pharmacodynamic effects from a systems pharmacology perspective, aiding in the global understanding of drug effects. This review focuses on the historical development of microdialysis as a method to quantify the pharmacologically very important unbound tissue concentrations and of recent findings relating to modeling microdialysis data to extrapolate from rodents to humans, understanding distribution of drugs in different tissues and disease conditions. Quantitative microdialysis developed very rapidly during the early 1990s. Method development was in focus in the early years including development of quantitative microdialysis, to be able to estimate true extracellular concentrations. Microdialysis has significantly contributed to the understanding of active transport at the blood-brain barrier and in other organs. Examples are presented where microdialysis together with modeling has increased the knowledge on tissue distribution between species, in overweight patients and in tumors, and in metabolite contribution to drug effects. More integrated metabolomic studies are still sparse within the microdialysis field, although a great potential for tissue and disease-specific measurements is evident.     

Lung microdialysis—A powerful tool for the determination of exogenous and endogenous compounds in the lower respiratory tract (mini-review)

In vivo measurement of concentrations of drugs and endogenous substances at the site of action has become a primary focus of research. In this context the minimal invasive microdialysis (MD) technique has been increasingly employed for the determination of pharmacokinetics in lung. Although lung MD is frequently employed to investigate various drugs and endogenous substances, the majority of lung MD studies were performed to determine the pharmacokinetic profile of antimicrobials that can be related to the importance of respiratory tract infections. For the lower respiratory tract various methods, such as surgical collection of whole lung tissue and bonchoalveolar lavage (BAL), are currently available for the determination of pharmacokinetics of antimicrobials. Head-to-head comparison of pharmacokinetics of antibiotics in lung revealed high differences between MD and conventional methods. MD might be regarded as a more advantageous approach because of its higher anatomical resolution and the ability to obtain dynamic time-vs-concentration profiles within one subject. However, due to ethical objections lung MD is limited to animals or patients undergoing elective thoracic surgery. From these studies it was speculated that the concentrations in healthy lung tissue may be predicted reasonably by the measurement of concentrations in skeletal muscle tissue. However, until now this was only demonstrated for beta-lactam antibiotics and needs to be confirmed for other classes of antimicrobials. In conclusion, the present review shows that MD is a promising method for the determination of antimicrobials in the lung, but might also be applicable for measuring a wide range of other drugs and for the investigation of metabolism in the lower respiratory tract.     

Muscle distribution of the neuromuscular blocker gallamine using microdialysis

Measurement of drug concentrations in target tissue has the potential to provide insight into the pharmacokinetics and pharmacodynamics of a drug. In this study, the distribution of the neuromuscular blocker, gallamine, into muscle tissue was investigated in urethane-anesthetized rats after an intravenous bolus dose (6 mg/kg). Microdialysis sampling was used to continuously determine gallamine concentrations in muscle interstitial fluid (MIF). In vivo microdialysis recovery of gallamine was determined as the relative loss of gallamine from the perfusate into muscle tissue after perfusion with gallamine (2 microg/mL). Recovery was determined in each rat before the pharmacokinetic studies. Terminal muscle sampling followed by homogenization was also performed to examine gallamine distribution within muscle tissue. All samples were assayed for gallamine using a validated high-performance liquid chromatography assay. Gallamine was rapidly distributed into MIF with a MIF-plasma partition coefficient of 0.9 +/- 0.1 (n = 6). By contrast, the estimated gallamine concentration in muscle tissue homogenate was only 23 +/- 5% (n = 5) of the concentration in MIF as estimated by microdialysis sampling at the terminal sampling time. These findings suggest that gallamine is not distributed uniformly within muscle but selectively distributes into MIF. Simulations using a hybrid physiologically based pharmacokinetic model which describes uptake of drug only into the interstitial space showed good agreement between predicted and observed concentration data obtained from microdialysis sampling, supporting the findings that gallamine selectively distributes into MIF. These studies demonstrate microdialysis combined with conventional terminal tissue sampling provides valuable information on intra-tissue drug distribution.     

Probenecid: an unexplained effect on cephalosporin pharmacology.

1 The influence of probenecid on serum levels and urinary excretion of orally administered cephradine and cefaclor has been investigated. 2 Probenecid caused serum levels of both antibiotics to be increased and also prolonged. Urinary excretion of antibiotic activity was slightly but not significantly decreased by probenecid during the initial 6 h postdosing. It was significantly increased in 6-12 h urine, but only a small percentage of the doses were excreted during that period. 3 The increased serum levels of antibiotic were greater than could be accounted for by reduced elimination rate alone. Possible mechanisms to account for increased circulating levels of antibiotic in the presence of probenecid are discussed in the light of previous observations on probenecid induced changes in tissue distribution of beta-lactam antibiotics.     

The chinchilla microdialysis model for the study of antibiotic distribution to middle ear fluid

In cases of slow or limited penetration of an antibiotic to the site of infection such as in acute otitis media (the middle ear), plasma levels of the agent may not reflect the concentrations that are relevant in determining clinical outcome. There is a need for a model that allows prediction of the time-course of unbound, pharmacologically active drug levels in middle ear fluid (MEF). This article introduces microdialysis as a sampling tool to measure unbound antibiotic concentrations in the MEF of the chinchilla, and briefly summarizes the results of studies of MEF penetration of a cephalosporin, a macrolide, and a ketolide antibiotic using this technique. The general concurrence of preliminary results of the chinchilla studies with clinical findings suggests that the chinchilla microdialysis model may be useful in predicting efficacy in patients.     

Intrabronchial Microdialysis: Effects of Probe Localization on Tissue Trauma and Drug Penetration into the Pulmonary Epithelial Lining Fluid

Recent intrabronchial microdialysis data indicate that the respiratory epithelium is highly permeable to drugs. Of concern is whether intrabronchial microdialysis disrupts the integrity of the respiratory epithelium and thereby alters drug penetration into the pulmonary epithelial lining fluid (PELF). The objective of this study was to investigate the effect of intrabronchial microdialysis on the integrity of the bronchial epithelium. Microdialysis sampling in PELF in proximal (n = 4) and distal bronchi (n = 4) was performed after intravenous inulin and florfenicol administration in anaesthetized pigs. Inulin was used as a marker molecule of permeability of the epithelium, and florfenicol was used as test drug. Bronchial tissue was examined by histopathology (distal and proximal bronchi) and gene expression analysis (RT‐qPCR, proximal bronchi) at the termination of the experiment (6.5 hr). The microdialysis probe caused overt tissue trauma in distal bronchi, whereas no histopathological lesions were observed in proximal bronchi. A moderate up‐regulation of the pro‐inflammatory cytokines IL1B, IL6 and acute‐phase reactant serum amyloid A was seen in proximal bronchi surrounding the microdialysis probes suggesting initiation of an inflammatory response. The observed up‐regulation is considered to have limited impact on drug penetration during short‐term studies. Inulin penetrated the respiratory epithelium in both proximal and distal bronchi without any correlation to histopathological lesions. Likewise, florfenicol penetration into PELF was unaffected by bronchial histopathology. However, this independency of pathology on drug penetration may not be valid for other antibiotics. We conclude that short‐term microdialysis drug quantification can be performed in proximal bronchi without disruption of tissue integrity.     

Microdialysis in peripheral tissues

The objective of this review is to survey the recent literature regarding the applications of microdialysis in pharmacokinetic studies and facilitating many other studies in peripheral tissues such as muscle, subcutaneous adipose tissue, heart, lung, etc. It has been reported extensively that microdialysis is a useful technique for monitoring free concentrations of compounds in extracellular fluid (ECF), and it is gaining popularity in pharmacokinetic and pharmacodynamic studies, both in experimental animals and humans. The first part of this review discusses the use of microdialysis technique for ECF sampling in peripheral tissues in animal studies. The second part of the review describes the use of microdialysis for ECF sampling in peripheral tissues in human studies. Microdialysis has been applied extensively to measure both endogenous and exogenous compounds in ECF. Of particular benefit is the fact that microdialysis measures the unbound concentrations in the peripheral tissue fluid which have been shown to be responsible for the pharmacological effects. With the increasing number of applications of microdialysis, it is obvious that this method will have an important place in studying drug pharmacokinetics and pharmacodynamics.     

Microdialysis in mice for drug delivery research

Intracerebral microdialysis was first performed in the mouse at the end of the 1980s. Most microdialysis studies on mice were confined to neuropharmacology and changes in neurotransmitter concentrations up to 1995, although pharmacological studies were done on other tissues like the skin, kidney and implanted tumors. The use of microdialysis in mice for pharmacokinetic and drug delivery studies owes much to the recent availability of genetically engineered mice, such as mice in which the genes encoding multiple drug resistance have been knocked out. The quantitative microdialysis of blood and various tissue fluids of the mouse is now feasible and the recent development of specific microdialysis devices for use in mice should facilitate its use in these small animals. This review covers the technical aspects of microdialysis in the mouse and includes references to many of the published studies on pharmacokinetics and drug delivery.     

Non-linear tissue binding of amikacin in rats: the effect of renal impairment

Amikacin levels in serum and tissues were determined in 115 Wistar rats, 70 with normal renal function (NRF) and the remaining 45 with terminal renal impairment (TRI). The results obtained in the animals with NRF show an accumulation of the antibiotic in all the tissues studied as compared with plasma levels, specially in the renal cortex and medulla. In the rats with TRI important alterations in the plasma and tissue kinetics of the antibiotics were observed. The plasma kinetics of amikacin in rats with TRI are characterised by significant alterations in the pharmacokinetic parameters, specially those defining the distribution processes of the antibiotic. In the tissues of the latter, a significant increase in the antibiotic concentration takes place, particularly in the renal cortex. The average half-lives of the antibiotic in the tissues of rats with TRI increase compared with the group of rats with NRF, though the difference are not so significant as in the case of the plasma half-life. The use of a specific kinetic distribution model, with linear and non-linear tissue binding, showed that significant variations occur in the partition coefficient and in the Michaelis-Menten parameters, which characterize the saturable binding of Amikacin to tissue in rats with NRF and TRI.     

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.     

Applicability of reverse microdialysis in pharmacological and toxicological studies

A recent application of microdialysis is the introduction of a substance into the extracellular space via the microdialysis probe. The inclusion of a higher amount of a drug in the perfusate allows the drug to diffuse through the microdialysis membrane to the tissue. This technique, actually called as reverse microdialysis, not only allows the local administration of a substance but also permits the simultaneous sampling of the extracellular levels of endogenous compounds. Local effects of exogenous compounds have been studied in the central nervous system, hepatic tissue, dermis, heart and corpora luteae of experimental animals by means of reverse microdialysis. In central nervous studies, reverse microdialysis has been extensively used for the study of the effects on neurotransmission at different central nuclei of diverse pharmacological and toxicological agents, such as antidepressants, antipsychotics, antiparkinsonians, hallucinogens, drugs of abuse and experimental drugs. In the clinical setting, reverse microdialysis has been used for the study of local effects of drugs in the adipose tissue, skeletal muscle and dermis. The aim of this review is to describe the principles of the reverse microdialysis, to compare the technique with other available methods and finally to describe the applicability of reverse microdialysis in the study of drugs properties both in basic and clinical research.