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

Developmental stage and infection status may affect drug distribution in the prostate of rats

Prostate inflammation is often treated with drugs which are ineffective. Antibacterial agents fail to reach the prostate epithelium, and the blood-prostate barrier (BPB) may affect the drug transport process. Factors affecting drug efficacy remain unclear.Rats were categorised into groups A and B, corresponding to adulthood and puberty, respectively. Group C included the model of chronic prostate infection. Dialysates of levofloxacin and cefradine were collected from the prostate gland and jugular vein and evaluated. Pharmacokinetic analysis was conducted.The free concentrations of antimicrobials in the prostate and plasma samples of all groups peaked at 20 min, then gradually decreased. The mean AUC0-tprostate/AUC0-tplasma ratio in the levofloxacin group were 0.86, 0.53, and 0.95, and the mean values of AUC0-∞prostate/AUC0-∞plasma ratio were 0.85, 0.63, and 0.97. The corresponding values in the cefradine group were 0.67, 0.30 and 0.84, and 0.66, 0.31, and 0.85, respectively. The mean values in group B were lower than those in group A, and those in group C were higher than those in group B.The maturity of the prostate may affect the ability of the drug to cross the BPB. Infection may disrupt the BPB, affecting drug permeability.

Multiple drug transporters contribute to the brain transfer of levofloxacin

AIMS

The aim of this study was to assess the influence of the major transporters at blood-brain barrier and blood-cerebrospinal fluid barrier on levofloxacin (LVFX) pharmacokinetics in rat. To explore the different effects of transporters on drug concentrations in cerebrospinal fluid (CSF) and brain extracellular fluid (ECF).

METHODS

High-performance liquid chromatography coupled with microdialysis was used to continuously and synchronously measure unbound concentrations of LVFX in rat blood, hippocampal ECF, and lateral ventricle CSF for comprehensive characterization of brain pharmacokinetics. The role of transporters in the brain efflux mechanism of LVFX was analyzed in the absence and presence of various transporter inhibitors.

RESULTS

Following LVFX (50 mg/kg) administration, the unbound partition coefficient of LVFX in brain ECF and CSF (K_p,uu,ECF and K_p,uu,CSF ) were 34.0 ± 1.7% and 41.2 ± 2.4%, respectively. When probenecid was coadministered with LVFX, the AUC and the mean residence time (MRT) in rat blood increased significantly (p < 0.05). After MK571 intervention, 1.35-fold and 1.16-fold increases in K_p,uu,ECF and K_p,uu,CSF were observed, respectively (p < 0.05). Treatment with Ko143 increased the levels of LVFX in brain ECF. The difference in LVFX concentration in brain ECF and CSF was <3-fold with or without treatment with transporter inhibitors.

CONCLUSION

Efflux of LVFX from the central nervous system (CNS) involves multidrug resistance-associated proteins (MRPs), breast cancer resistance protein (BCRP), and organic anion transporters (OATs). MRPs play an important role in mediating the brain/CSF-to-blood efflux of LVFX. LVFX concentrations in CSF can be used as a surrogate to predict the concentrations inside brain parenchyma.

Preparation and characterization of 2-hydroxyethyl starch microparticles for co-delivery of multiple bioactive agents

The present study reports the generation of 2-hydroxyethyl starch microparticles for co-delivery and controlled release of multiple agents. The obtained microparticles are characterized by using Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray diffraction analysis, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. By using ofloxacin and ketoprofen as drug models, the release sustainability of the microparticles is examined at pH 1.2, 5.4, and 6.8 at 37 °C, with Fickian diffusion being found to be the major mechanism controlling the kinetics of drug release. Upon being loaded with the drug models, the microparticles show high efficiency in acting against Escherichia coli and Bacillus cereus. The results suggest that our reported microparticles warrant further development for applications in which co-administration of multiple bioactive agents is required.

Determination of levofloxacin by HPLC with fluorescence detection in human breast milk

Aim: A new HPLC method with fluorescence detection has been developed and validated for the determination of levofloxacin, one of the fluoroquinolone class antibiotics, in breast milk. Materials & methods: Chromatographic separation was carried out on a reversed phase C18 column with acetonitrile and 10 mM o-phosphoric acid (25:75, v/v) mobile phase composition. Moxifloxacin was used as internal standard and the peaks were detected by fluorescence detection. Results & conclusion: Calibration graph was found linearly within the range of 2.5-500 ng/ml. Limit of detection and limit of quantification were found to be 0.63 and 2.11 ng/ml, respectively. Mean absolute recovery was 96.18%. The developed method has been successfully applied to the determination of levofloxacin in human breast milk taken from two healthy volunteers.

Levofloxacin in veterinary medicine: a literature review

A potent third-generation antimicrobial fluoroquinolone drug, levofloxacin was introduced into human clinical practice in 1993. Levofloxacin is also used in veterinary medicine, however its use is limited: it is completely banned for veterinary use in the EU, and used extralabel in only companion animals in the USA. Since its introduction to clinical practice, many studies have been published on levofloxacin in animal species, including pharmacokinetic studies, tissue drug depletion, efficacy, and animal microbial isolate susceptibility to levofloxacin. This literature overview highlights the most clinically relevant and scientifically important levofloxacin studies linked to the field of veterinary medicine.

Pharmacokinetic and tissue analyses of levofloxacin in sheep (Ovis aries Linnaeus) after multiple-dose administration

The aim of this study was to assess the pharmacokinetic profile of LFX in sheep after intravenous (IV) and oral (PO) administration of 2 mg/kg LFX once a day for 5 days and to evaluate its tissue depletion in the muscles, heart, liver, lungs, and kidneys. Twenty healthy female sheep were randomly divided into two equal groups. Each group was further randomly subdivided into two equal subgroups (n = 5). Group 1 was used for blood collection and underwent a crossover design (2 × 2 Latin square). Group 2 was randomly subdivided into two equal subgroups (n = 5) for IV and PO route respectively, and used for tissue collection. A single sheep was sacrificed at each time point and the organs were harvested. Samples were analyzed using a validated HPLC method with fluorescence detection. LFX administered orally was rapidly absorbed with a peak plasma concentration of 2866 ± 239 ng/mL and an absolute oral bioavailability of 114 ± 27.7%. The pharmacokinetic estimates were comparable between PO and IV administration. According to the pharmacokinetic/pharmacodynamic surrogate index (area under the curve / minimum inhibitory concentration) of 100-125, LFX has the potential to be an effective treatment for infections caused by bacteria with a MIC of 0.049-0.061 μg/mL. LFX was detected for up to 48 h in all the tissues samples. The kidney had the highest LFX concentration after IV and PO administration. The AUC_{tissue/plasma} ratio was lower than 1 in all tissues indicating absence of LFX tissue accumulation.

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.

Analytical Methods for Determining Third and Fourth Generation Fluoroquinolones: A Review

ABSTRACT

Fluoroquinolones of the third and fourth generation posses wide bactericidal activity. Monitoring concentrations of antibacterial agents provides effective therapy and prevents the increase of bacterial resistance to antibiotics. The pharmacodynamic parameters that best describe fluoroquinalone activity are AUC/MIC and Cmax/MIC. Determining the level of this type of drug is essential to reach the effective concentration that inhibits the growth of bacteria. Determining the pharmaceutical formulation confirms the purity of a substance. Many methods have been developed to determine the level of these substances. They involve mainly the following analytical techniques: chromatography, capillary electrophoresis, and spectroscopy. The separation techniques were combined with different measuring devices, such as ultraviolet (UV), fluorescence detector (FLD), diode array detector (DAD), and mass spectrometry (MS). The analytical procedures require proper sample pre-conditioning such as protein precipitation, extraction techniques, filtration, or dilution. This paper reviews the reported analytical methods for the determining representatives of the third and fourth generation of fluoroquinolones. Attention was paid to pre-conditioning of the samples and the applied mobile phase. This report might be helpful in the selection of the proper procedure in determining the abovementioned drugs in different matrices.

GRAPHICAL ABSTRACT

Prediction of the pharmacokinetics and tissue distribution of levofloxacin in humans based on an extrapolated PBPK model

This study developed a physiologically based pharmacokinetic (PBPK) model in intraabdominally infected rats and extrapolated it to humans to predict the levofloxacin pharmacokinetics and penetration into tissues. Twelve male rats with intraabdominal infections induced by Escherichia coli received a single dose of 50 mg/kg body weight of levofloxacin. Blood plasma was collected at 5, 10, 20, 30, 60, 120, 240, 480 and 1440 min after injection, respectively. A PBPK model was developed in rats and extrapolated to humans using GastroPlus software. The predictions were assessed by comparing predictions and observations. In the plasma concentration-versus-time profile of levofloxacin in rats, C max was 23.570 μg/ml at 5 min after intravenous injection, and t1/2 was 2.38 h. The plasma concentration and kinetics in humans were predicted and validated by the observed data. Levofloxacin penetrated and accumulated with high concentrations in the heart, liver, kidney, spleen, muscle and skin tissues in humans. The predicted tissue-to-plasma concentration ratios in abdominal viscera were between 1.9 and 2.3. When rat plasma concentrations were known, extrapolation of a PBPK model was a method to predict the drug pharmacokinetics and penetration in humans. Levofloxacin had good penetration into the liver, kidney and spleen as well as other tissues in humans. This pathological model extrapolation may provide a reference for the study of antiinfective PK/PD. In our study, levofloxacin penetrated well into abdominal organs. Also ADR monitoring should be implemented when using levofloxacin.

Quantitative determination of unbound levofloxacin by simultaneous microdialysis in rat pancreas after intravenous and oral doses

OBJECTIVE

We compared the pharmacokinetic profile of unbound levofloxacin in rat pancreas after an oral dose with that after an intravenous dose to determine if oral administration of levofloxacin could potentially be used.

METHOD

Levofloxacin was administered either intravenously or orally into male Sprague-Dawley rats at the concentration of 42 mg/kg per day, mimicking the human dose of 400 mg/day. The concentrations of levofloxacin in extracellular fluid (ECF) of rat pancreatic tissues were determined using microdialysis coupled with high-performance liquid chromatography (HPLC). Levofloxacin was equally distributed into ECF of rat pancreatic tissues with either intravenous route (AUCpancreas /AUCblood , 0.97 ± 0.02) or oral route (AUCpancreas /AUCblood , 0.96 ± 0.03).

KEY FINDINGS

The penetration rates (PR) of pancreas-to-blood on the same target site between the two routes were the same. The intravenous antibiotic AUC/MIC ratios of common Gram-positive pancreatic bacteria ranged from 83.43 to 667.44; meanwhile, the ratio of common Gram-negative pancreatic bacteria ranged from 41.71 to 2669.74. The oral antibiotic AUC/MIC ratios for common gram-positive and Gram-negative pancreatic bacteria were from 78.54 to 628.31, and 39.27 to 2513.22, respectively (P > 0.05).

CONCLUSIONS

Intravenous administration had similar penetration efficacy to oral administration at an equivalent dose. Furthermore, levofloxacin had a good penetration through the blood-pancreas barrier.

Disposition kinetics of levofloxacin in sheep after intravenous and intramuscular administration

The present study was planned to investigate the disposition kinetics of levofloxacin in plasma of female native Barky breed sheep after single intravenous (IV) and intramuscular (IM) administration of 4 mg/kg body weight. The concentrations of levofloxacin in the plasma were measured using high-performance liquid chromatography (HPLC) with a UV detector on samples collected at 0, 0.08, 0.16, 0.33, 0.5, 1, 2, 4, 6, 8, 10, 12, 18, 24, 32, and 48 h after treatment. Following intravenous injection, the decline in plasma drug concentration was biexponential with half-lives of (t_1/2α) 0.33 ± 0.12 h and (t_1/2β) 3.29 ± 0.23 h for distribution and elimination phases, respectively. The volume of distribution at steady state V_(d(ss)) was 0.86 ± 0.23 l/kg. After intramuscular administration of levofloxacin at the same dose, the peak plasma concentration (C_max) was 3.1 ± 0.35 μg/mL and was obtained at 1.64 ± 0.29 h (T_max), the elimination half-life (T_1/2el) was 3.58 ± 0.30 h, and AUC was 20.24 ± 1.31 μg.h/mL. The systemic bioavailability was 91.35 ± 6.81 %. In vitro plasma protein binding was 23.74%. When approved therapy fails, levofloxacin may be used in some countries for therapy of food animals, however, that is not true in the US.

Rapid and sensitive spectrofluorimetric determination of enrofloxacin, levofloxacin and ofloxacin with 2,3,5,6-tetrachloro-p-benzoquinone

A highly sensitive spectrofluorimetric method was developed for the first time, for the analysis of three fluoroquinolones (FQ) antibacterials, namely enrofloxacin (ENR), levofloxacin (LEV) and ofloxacin (OFL) in pharmaceutical preparations through charge transfer (CT) complex formation with 2,3,5,6-tetrachloro-p-benzoquinone (chloranil,CLA). At the optimum reaction conditions, the FQ-CLA complexes showed excitation maxima ranging from 359 to 363nm and emission maxima ranging from 442 to 488nm. Rectilinear calibration graphs were obtained in the concentration range of 50-1000, 50-1000 and 25-500ngmL(-1) for ENR, LEV and OFL, respectively. The detection limit was found to be 17ngmL(-1) for ENR, 17ngmL(-1) for LEV, 8ngmL(-1) for OFL, respectively. Excipients used as additive in commercial formulations did not interfere in the analysis. The method was validated according to the ICH guidelines with respect to specificity, linearity, accuracy, precision and robustness. The proposed method was successfully applied to the analysis of pharmaceutical preparations. The results obtained were in good agreement with those obtained using the official method; no significant difference in the accuracy and precision as revealed by the accepted values of t- and F-tests, respectively.

Methods for the analysis of fluoroquinolones in biological fluids

Methods for the analysis of ten selected fluoroquinolone antibiotics in biological fluids are reviewed. Approaches for sample preparation, detection methods, limits of detection and quantitation, and recovery information are provided for both single analyte and multi-analyte fluoroquinolone methods.

Rapid chiral separation and impurity determination of levofloxacin by ligand-exchange chromatography

A sensitive, simple, and accurate method for determination of levofloxacin and its (R)-enantiomer was developed to determine the chiral impurity of levofloxacin in Cravit Tablets material by ligand-exchange high performance liquid chromatography. The effects of different kinds of ligands, concentration of ligands in mobile phase, organic modifier, pH of mobile phase, and temperature on enantioseparation were investigated and evaluated. Chiral separation was performed on a conventional C(18) column, where the mobile phase consisted of a methanol-water solution (containing 10 mmol L(-1)l-leucine and 5 mmol L(-1) copper sulfate) (88:12, v/v) and its flow-rate was set at 1.0 mL min(-1). The conventional C(18) column offers baseline separation of two enantiomers with a resolution of 2.4 in less than 20 min. Thermodynamic data (DeltaDeltaH and DeltaDeltaS) obtained by Van't Hoff plots revealed the chiral separation is an enthalpy-controlled process. The standard curves showed excellent linearity over the concentration range from 0.5 to 400 mg L(-1) for levofloxacin and its (R)-enantiomer. The linear correlation equations are: y=1.33 x 10(5)x+6297 (r=0.9991) and y=1.34 x 10(5)x+3565 (r=0.9997), respectively. The relative standard deviation (RSD) of the method was below 2.3% (n=3).

Validation of a levofloxacin HPLC assay in plasma and dialysate for pharmacokinetic studies

An HPLC method with fluorescence detection suitable for routine determination of levofloxacin in plasma and dialysate has been validated. Sample preparation was assured by one-step protein precipitation for plasma or direct injection of the dialysate solution, respectively. Separation occurred on an YMC Pro C18 RP column (150 mm x 2 mm) with an acidic binary gradient mobile phase and detection at excitation and emission wavelengths of 296 and 504 nm. The assay was linear between 0.1 and 6 microg/ml for plasma and 0.1 and 5 microg/ml for dialysate with intra- and inter-day precision and accuracy lower than 10%. No degradation of levofloxacin was observed under the applied conditions for both matrices. The method was successfully applied to an in vitro pharmacokinetic study and patient samples as well.

Hydrophilic interaction liquid chromatography–tandem mass spectrometry for the determination of levofloxacin in human plasma

A rapid, sensitive and selective hydrophilic interaction liquid chromatography-tandem mass spectrometric (HILIC-MS/MS) method for the determination of levofloxacin in human plasma was developed. Levofloxacin and ciprofloxacin (internal standard) were extracted from human plasma with dichloromethane and analyzed on an Atlantis HILIC Silica column with the mobile phase of acetonitrile-ammonium formate (100 mM, pH 6.5) (82:18 v/v). The analytes were detected using an electrospray ionization tandem mass spectrometry in the multiple-reaction-monitoring mode. The standard curve was linear (r>0.999) over the concentration range of 10.0-5000 ng/ml. The lower limit of quantification for levofloxacin was 10.0 ng/ml using 20 microl plasma sample. The coefficient of variation and relative error for intra- and inter-assay at four QC levels were 2.9-7.8% and -7.3% to -2.2%, respectively. The recoveries of levofloxacin and ciprofloxacin were 55.2% and 77.3%, respectively. This method was successfully applied to the pharmacokinetic study of levofloxacin in humans.

Effect of ethanol on fluoroquinolone efficacy in a rat model of pneumococcal pneumonia

This investigation compared the effect of ethanol on fluoroquinolone antibiotic efficacy and pharmacodynamics in an ethanol-fed rat model of pneumococcal pneumonia. Male Sprague-Dawley rats received a liquid diet containing 36% of total calories as ethanol. Paired controls (pair-fed controls) were fed a liquid diet without ethanol or received rat chow. Diets began 7 days before and continued for 10 days after transtracheal infections with 10 times the 50% lethal dose of type 3 Streptococcus pneumoniae. Beginning 18 h after infection, the rats received once daily subcutaneous phosphate-buffered saline, levofloxacin, moxifloxacin, or trovafloxacin at 50 or 100 mg/kg of body weight. White blood cell counts were determined, blood samples were collected for culture, and mortality was recorded. Additional rats were killed on day 5 for pharmacodynamic studies and quantitative cultures of bronchoalveolar lavage fluid. Bacteremia occurred by day 3 in 20 of 22 untreated rats. All 22 untreated rats died by day 9. Moxifloxacin treatment was effective in all diet groups at both the 50- and 100-mg/kg doses. In contrast, 50-mg/kg doses of levofloxacin and trovafloxacin improved survival in ethanol-fed rats but were ineffective in chow-fed rats. High-dose trovafloxacin at 100 mg/kg was associated with increased mortality in pair-fed rats. The free-fraction area under the concentration-time curve/MIC ratio exceeded 50 with all antibiotics in the ethanol group but dropped below 30 with levofloxacin and trovafloxacin in the pair- and chow-fed rats, with higher mortality. Achievement of adequate antibiotic-free fraction area under the concentration-time curve/MIC ratios helps overcome ethanol-induced immune defects induced in experimental pneumococcal pneumonia.

Investigation of chromatographic conditions for the separation of ofloxacin and its degradation products

A sensitive, precise, and accurate reversed-phase high-performance liquid chromatography (RP-HPLC) method was developed and validated for simultaneous determination of fluoroquinolone antibacterial ofloxacin and its degradation products: decarboxy ofloxacin, 9-piperazino ofloxacin, des-methyl ofloxacin, and ofloxacin-N-oxide. The proposed RP-HPLC method allowed separation of all five compounds simultaneously with the total time of the analysis not more than 15 min. The relative standard deviation (RSD) values for quantification of DOF, POF, MOF, OF, and NOF were of 0.77, 0.58, 0.51, 0.10, and 0.70%, respectively, indicating a good precision of the method. The limits of detection for DOF, POF, MOF, OF, and NOF were 0.10, 0.13, 0.06, 0.03, and 0.03 microg mL(-1), respectively. The described method can be used for simultaneous identification and quantification of all analysed compounds in different pharmaceutical formulations.

Simple extractive colorimetric determination of levofloxacin by acid-dye complexation methods in pharmaceutical preparations

Two simple and sensitive extractive spectrophotometric methods have been described for the assay of levofloxacin (LVFX) either in pure form or in pharmaceutical formulations. The developed methods involve formation of colored chloroform extractable ion-pair complexes (1:1 and 1:2 drug/dye) of levofloxacin with bromophenol blue (BPB) and bromocresol green (BCG) in aqueous acidic medium. The extracted complexes showed absorbance maxima at 424 and 428 nm for LVFX-BPB and LVFX-BCG, respectively. Beer's law is obeyed in the concentration ranges 1.85-31.5 and 1.85-25 microg ml(-1) with BPB and BCG, respectively. The methods have been applied to the determination of drug in commercial tablets. Results of analysis were validated statistically. The excipients present in the formulations do not interfere with the assay procedure.

Quantitative determinations of levofloxacin and rifampicin in pharmaceutical and urine samples using nuclear magnetic resonance spectroscopy

Rapid, specific and simple methods for determining levofloxacin and rifampicin antibiotic drugs in pharmaceutical and human urine samples were developed. The methods are based on (1)H NMR spectroscopy using maleic acid as an internal standard and DMSO-d6 as NMR solvent. Integration of NMR signals at 8.9 and 8.2 ppm were, respectively, used for calculating the concentration of levofloxacin and rifampicin drugs per unit dose. Maleic acid signal at 6.2 ppm was used as the reference signal. Recoveries of (97.0-99.4)+/-0.5 and (98.3-99.7)+/-1.08% were obtained for pure levofloxacin and rifampicin, respectively. Corresponding recoveries of 98.5-100.3 and 96.8-100.0 were, respectively, obtained in pharmaceutical capsules and urine samples. Relative standard deviations (R.S.D.) values < or =2.7 were obtained for analyzed drugs in pure, pharmaceutical and urine samples. Statistical Student's t-test gave t-values < or =2.87 indicating insignificant difference between the real and the experimental values at the 95% confidence level. F-test revealed insignificant difference in precisions between the developed NMR methods and each of fluorimetric and HPLC methods for analyzing levofloxacin and rifampicin.

Pharmacokinetics of levofloxacin after single intravenous and repeat oral administration to cats

The pharmacokinetic properties of the fluoroquinolone levofloxacin, were investigated in five cats after single intravenous and repeat oral administration at a daily dose of 10 mg/kg. Levofloxacin serum concentration was analyzed by microbiological assay using Klebsiella pneumoniae ATCC 10031 as test microorganism. Serum levofloxacin disposition after intravenous and oral dosing was best fitted to a bicompartmental and a monocompartmental open models with first-order elimination, respectively. After intravenous administration, distribution was rapid (t(1/2(d)) 0.26 +/- 0.18 h) and wide as reflected by the steady-state volume of distribution of 1.75 +/- 0.42 L/kg. Drug elimination was slow with a total body clearance of 0.14 +/- 0.04 L/h.kg and a t(1/2) for this process of 9.31 +/- 1.63 h. The mean residence time was of 12.99 +/- 2.12 h. After repeat oral administration, absorption half-life was of 0.18 +/- 0.12 h and Tmax of 1.62 +/- 0.84 h. The bioavailability was high (86.27 +/- 43.73%) with a peak plasma concentration at the steady state of 4.70 +/- 0.91 microg/mL. Drug accumulation was not significant after four oral administrations. Estimated efficacy predictors for levofloxacin after either intravenous or oral administration indicate a good profile against bacteria with a MIC value below of 0.5 microg/mL. However, for microorganisms with MIC values of 1 microg/mL it would be efficacious only when administered intravenously.

Microdialysis—theoretical background and recent implementation in applied life-sciences

In the past decade microdialysis has become a method of choice in the study of unbound tissue concentrations of both endogenous and exogenous substances. Microdialysis has been shown to offer information about substances directly at the site of action while being well tolerable and safe. The large variety of its field of application has been demonstrated. However, a few challenges have to be met to make this method generally applicable in routine applications. This review will provide an overview over theoretical aspects that have to be considered during the implementation of microdialysis. Moreover, a comparison between microdialysis and other tissue sampling techniques will demonstrate advantages and limitations of the methods mentioned. Subsequently, it will present a critical synopsis of a variety of scientific/biomedical applications of this method with emphasis on the most recent literature, focussing on target tissues while giving examples of substances examined. It is concluded that microdialysis will be of great value in future investigations of pharmacokinetics, pharmacodynamics and in monitoring of disease status and progression.

Direct determination of five fluoroquinolones in chicken whole blood and in veterinary drugs by HPLC

A direct, accurate, and sensitive chromatographic analytical method for the quantitative determination of five fluoroquinolones (enoxacin, ofloxacin, norfloxacin, ciprofloxacin, and enrofloxacin) in chicken whole blood is proposed in the present study. For quantitative determination lamotrigine was used as internal standard at a concentration of 20 ng/microL. The developed method was successfully applied to the determination of enrofloxacin, as the main component of commercially available veterinary drugs. Fluoroquinolone antibiotics were separated on an Inertsil (250 x 4 mm) C8, 5 microm, analytical column, at ambient temperature. The mobile phase consisted of a mixture of citric acid (0.4 mol L(-1))-CH3OH-CH3CN (87:9:4% v/v) leading to retention times less than 14 min, at a flow rate 1.4 mL min(-1). UV detection at 275 nm provided limits of detection of 2 ng/mL per 20 microL injected volume for enoxacin, norfloxacin, and ciprofloxacin, 0.4 ng/mL for ofloxacin, and 4 ng/mL for enrofloxacin. Preparation of chicken blood samples is based on the deproteinization with acetonitrile while the pharmaceutical drug was simply diluted with water. Peaks of examined analytes in real samples were identified by means of a photodiode array detector. The method was validated in terms of within-day (n=6) precision and accuracy after chicken whole blood sample deproteinization by CH3CN. Using 50 microL of chicken blood sample, recovery rates at fortification levels of 40, 60, and 80 ng ranged from 86.7% to 103.7%. The applicability of the method was evaluated using real samples from chicken under fluoroquinolone treatment.

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.