Human urinary excretion kinetics of the antimycotic climbazole: Biomonitoring of two new metabolites after oral and dermal dosage.

Climbazole is an antimycotic compound used in cosmetic products as a preservative or as an active ingredient in anti-dandruff (AD) formulations. In this study we provide human toxicokinetic data on climbazole. Using our previously published analytical method, we investigated the urinary excretion of two climbazole metabolites, (OH)2-climbazole and cx-OH-climbazole, for 48 h after oral ingestion (n = 5, 49-77 µg/kg bw) and for 72 h after dermal application of either a climbazole-containing rinse-off AD shampoo or a leave-on hair tonic (n = 2×3). In total, 23.9 % (18.0-33.4 %) of the oral dose were excreted as the two abovementioned metabolites over 48 h. In one volunteer, who used an over-the-counter phytopharmaceutical, metabolite excretion was about three times lower and we found influences on diastereoselectivity of (OH)2-climbazole formation using a modified analytical method. After dermal application, urinary concentration maxima occurred considerably later than after oral intake. The two different dermal exposure scenarios also revealed a relevance of exposure duration and product formulation on the systemic availability of climbazole. Back-calculated oral-dose-equivalent intakes from the dermal exposures showed a maximum climbazole intake of 18.5 µg/kg bw/d after hair tonic use, or 6.6 µg/kg bw/d after AD shampoo application.

A comparison of chiral resolution of antifungal agents on different polysaccharide chiral columns under various mobile phase modes: Application in the biological samples.

The current article describes the chiral separation of tioconazole, miconazole, isoconazole, sertaconazole and terconazole, with Lux i-Cellulose 5 and Lux i-Amylose-1 chiral columns under organic polar, normal and reversed mobile phases modes. The mobile phase flow rate was 1 mL/min with 230 nm detection at 25 ± 1 °C temperature. The polar organic mobile phases offered certain advantages for separation such as short analysis time, order of elution, high plate numbers and favorable signal to noise ratio. The values of k, α and Rs were ranged from 0.6 to 7.87, 1.10 to 1.62 and 0.37 to 5.72 in polar organic, 0.15 to 43.86, 1.02 to 2.01 and 0.36 to 8.03 in normal, and 0.34 to 15.99, 1.03 to 1.40 and 0.59 to 4.18 in reversed phases modes, respectively. The reported methods were applied in urine samples and the results were satisfactory. The reported methods were applied to the analysis of urine samples.

Electrocatalytic evaluation of graphene oxide warped tetragonal t-lanthanum vanadate (GO@LaVO4) nanocomposites for the voltammetric detection of antifungal and antiprotozoal drug (clioquinol).

Metastable and rarely reported GO warped tetragonal phase t-lanthanum vanadate nanocomposites (GO@LaVO4-NCs) are reported for the sensitive electrochemical determination of antifungal drug Clioquinol (CQ). The hydrothermal method was adopted for synthesis of GO@LaVO4-NCs. The electrochemical performance of CQ was examined using cyclic voltammetry (CV) and differential plus voltammetry (DPV) at GO@LaVO4-NCs modified glassy carbon electrode (GCE). The electrocatalytic oxidation of CQ at the GO@LaVO4-NCs/GCE shows the highest anodic peak current at a potential of +0.51 V vs. Ag/AgCl. The proposed sensor provides excellent sensitivity of 4.1894 µA µM-1 cm-2, a very low detection limit (LOD) of 2.44 nM, and a wide range of 25 nM to 438.52 µM towards CQ detection. Finally, the detection of CQ in biological media was successfully done using the GO@LaVO4-NCs/GCE and possesses recoveries of 94.67-98.0%.

Caspofungin PK in critically ill patients after the first and fourth doses: suggestions for therapeutic drug monitoring?

We describe caspofungin pharmacokinetics (PK) after the first and fourth doses in 20 critically ill septic patients. Monte Carlo simulation was used to analyze the probability of target attainment (PTA) (AUC/MIC > 865) for Candida spp. Caspofungin concentrations were analyzed by HPLC in plasma and urine. A great variability in PK parameters was observed after both doses. Patients were divided in two groups according to their AUC values (AUC ≤ 75 mg h/L cut-off). In the low-AUC group Cmax, Cmin and AUC were lower, while Vd and Cl were higher than in the high-AUC group (p < 0.05, both at day 1 and 4). The mean 24-h urinary recovery of the drug was 8 ± 6.3% (day1) and 9.8 ± 6.3 (day4). Monte Carlo simulation analysis (0.03-1 mg/L MIC-range) showed that PTA was guaranteed only for MICs ≤ 0.03 mg/L in the low-AUC group, and for MICs ≤ 0.06 mg/L in the high-AUC group. No group had a PTA ≥ 90% for 0.125 mg/L MIC (the epidemiological cut-off). Mortality was higher in low-AUC group (p < 0.01). In our 'real-world' population, no clinical data can predict which patient will have lower, suboptimal caspofungin exposure, therefore we suggest TDM to optimize caspofungin therapy and reduce the risk of selecting resistances (CEAVC, 32366/2015; OSS.15.114, NCT03798600).

Drug-drug interaction and doping: Effect of non-prohibited drugs on the urinary excretion profile of methandienone.

The potential consequences of drug-drug interactions on the excretion profile of the anabolic androgenic steroid methandienone (17ß-hydroxy-17α-methylandrosta-1,4-dien-3-one) are discussed. More specifically, we have evaluated by in vitro and in vivo experiments the effects of 7 non-prohibited drugs (fluconazole, ketoconazole, itraconazole, miconazole, fluoxetine, paroxetine, and nefazodone) on the main metabolic pathways of methandienone. These are selected among those most commonly used by the athletes. The in vitro assays were based on the use of human liver microsomes, specific recombinant enzyme isoforms of cytochrome P450 and uridine 5'-diphospho-glucuronosyl-transferase. The in vivo study was performed by analyzing urines collected after the oral administration of methandienone with and without the co-administration of ketoconazole. Methandienone and its metabolites were determined by liquid chromatography-mass spectrometry-based techniques after sample pretreatment including an enzymatic hydrolysis step (performed only for the investigation on phase II metabolism) and liquid/liquid extraction with t-butyl methyl-ether. The results from the in vitro experiments showed that the formation of the hydroxylated and dehydrogenated metabolites was significantly reduced in the presence of itraconazole, ketoconazole, miconazole and nefazodone, whereas the production of the 18-nor-hydroxylated metabolites and glucuronidation reactions was reduced significantly only in the presence of ketoconazole and miconazole. The analysis of the post-administration samples confirmed the in vitro observations, validating the hypothesis that drug-drug interaction may cause significant alterations in the metabolic profile of banned drugs, making their detection during doping control tests more challenging.

A rapid MCM-41 dispersive micro-solid phase extraction coupled with LC/MS/MS for quantification of ketoconazole and voriconazole in biological fluids.

A rapid dispersive micro-solid phase extraction (D-µ-SPE) combined with LC/MS/MS method was developed and validated for the determination of ketoconazole and voriconazole in human urine and plasma samples. Synthesized mesoporous silica MCM-41 was used as sorbent in d-µ-SPE of the azole compounds from biological fluids. Important D-µ-SPE parameters, namely type desorption solvent, extraction time, sample pH, salt addition, desorption time, amount of sorbent and sample volume were optimized. Liquid chromatographic separations were carried out on a Zorbax SB-C18 column (2.1 × 100 mm, 3.5 µm), using a mobile phase of acetonitrile-0.05% formic acid in 5 mm ammonium acetate buffer (70:30, v/v). A triple quadrupole mass spectrometer with positive ionization mode was used for the determination of target analytes. Under the optimized conditions, the calibration curves showed good linearity in the range of 0.1-10,000 µg/L with satisfactory limit of detection (≤0.06 µg/L) and limit of quantitation (≤0.3 µg/L). The proposed method also showed acceptable intra- and inter-day precisions for ketoconazole and voriconazole from urine and human plasma with RSD ≤16.5% and good relative recoveries in the range 84.3-114.8%. The MCM-41-D-µ-SPE method proved to be rapid and simple and requires a small volume of organic solvent (200 µL); thus it is advantageous for routine drug analysis.

Monitoring of antifungal drugs in biological samples using ultrasonic-assisted supramolecular dispersive liquid-liquid microextraction based on solidification of a floating organic droplet.

A new method for the simultaneous determination of the three antifungal drugs using ultrasonic-assisted supramolecular dispersive liquid-liquid microextraction based on solidification of a floating organic droplet (UASMDLLME-SFO) was proposed. The supramolecular solvents produced from reversed micelles of 1-dodecanol (extraction solvent) in tetrahydrofuran (THF) were injected into the aqueous sample solution. Reverse micelle coacervates were produced in situ through self-assembly processes. The antifungal drugs were extracted from the aqueous sample into a supramolecular solvent. Sonication accelerated the mass transfer of the target analytes into the supramolecular solvent phase and enhanced the dispersion process. Some parameters affecting the extraction efficiency such as type and volume of the extraction solvent, pH, volume of the disperser solvent and ultrasound extraction time were investigated. Under optimum conditions, the limits of detections for ketoconazole, clotrimazole and miconazole ranged from 0.08 to 1.3µgL(-1) and the relative standard deviations (RSDs, n=5)<6% were obtained. The method was successfully applied for preconcentration of the three drugs in biological and water samples.

Does the Anesthetic Urethane Influence the Pharmacokinetics of Antifungal Drugs? A Population Pharmacokinetic Investigation in Rats.

The aim of this paper was to analyze the impact of anesthesia induced by urethane on pharmacokinetics (PK) parameters of fluconazole (FCZ), mostly eliminated via renal excretion and voriconazole (VRC), eliminated mainly by hepatic metabolism. FCZ and VRC PK were investigated after administration of 10 mg/kg i.v. and 5 mg/kg i.v. doses to awake and urethane anesthetized Wistar rats (n = 6 per group), respectively. After dosing, blood samples were collected up to 18 h (FCZ) or 12 h (VRC) and the plasma data analysis was performed using the software MONOLIX v. 4.2.2. The population PK parameters and microconstants were determined by fitting plasma concentration-time profiles to two-compartment model for FCZ and three-compartment model for VRC. Fitting of FCZ plasma profiles after dosing to awake and anaesthetized animals resulted in a volume of distribution (V) of 9.3 and 8.1 L/kg, and k10 values of 0.12 and 0.14 h(-1) , respectively. VRC plasma profiles in awake and anaesthetized showed V 8.7 of and 7.6 L/kg, and k10 of 0.15 and 0.16 h(-1) , respectively. No statistical differences between plasma PK parameters and microconstants for the same drug in both animal conditions studied were observed (α = 0.05).

Candidúria em adultos e crianças: prevalência e suscetibilidade a antifúngicos em pacientes ambulatoriais de Jataí-GO / Candiduria in adults and children: prevalence and antifungal susceptibility in outpatient of Jataí-GO

Introduction: The term candiduria refers to the presence of yeast in urine and Candida albicans is the most common agent. In general, routine laboratories do not perform identification and cultivation of yeast. Objectives: To determine the prevalence of Candida species and to evaluate the antifungal susceptibility of the species isolated in urine of outpatients Jataí-GO, between January-October 2013. Material and method: Urine samples containing fungal structures were plated out on Sabouraud agar with chloramphenicol. Differentiation was taken with the urease test, nitrogen and carbon sources assimilation, germ tube test, morphology on cornmeal agar and chromogenic agar cultivation. Susceptibility was evaluated at antifungal itraconazole, fluconazole, amphotericin B and ketoconazole. Results: 1,215 urine tests were performed, and 64 had fungal structures (5.3%). Two samples were lost, thus here we considered 62 isolates. From this total, 43 were identified as C. albicans (67.2 %), eight C. glabrata (12.5 %), five C. krusei (7.8%), three C. tropicalis (4.7%), and three could not determine the species (4.7%). Amphotericin B and ketoconazole inhibited 94.9% of the isolates. On the other hand, 55.9% and 54.2 % were resistant to itraconazole and fluconazole, respectively. The resistance rates of both fluconazole and itraconazole for C. glabrata and C. albicans, as fluconazole for C. albicans and C. krusei, showed significant differences (p < 0.05). Conclusion: These data demonstrate the importance of conducting a full identification and susceptibility to antifungal agents in samples with yeast infection...

Introdução: O termo candidúria designa a presença de leveduras na urina e Candida albicans é o agente mais comum. Em geral, os laboratórios de rotina não realizam o cultivo e a identificação da levedura. Objetivos: Determinar a prevalência de espécies de Candida e avaliar o perfil de sensibilidade aos antifúngicos das espécies isoladas em urina de pacientes ambulatoriais do município de Jataí-GO, entre janeiro e outubro de 2013. Material e método: Amostras de urina que continham estruturas fúngicas foram semeadas em ágar Sabouraud com cloranfenicol. A diferenciação foi feita com provas da urease, assimilação de fontes de nitrogênio e carbono, tubo germinativo, morfologia em ágar fubá e cultivo em ágar cromogênico. Foi avaliada a sensibilidade aos antifúngicos itraconazol, fluconazol, anfotericina B e cetoconazol. Resultados: Foram realizados 1.215 exames de urina, sendo que 64 apresentaram estruturas fúngicas (5,3%). Houve perda de duas amostras, assim, considerou-se 62 isolados. Desse total, 43 foram identificadas como C. albicans (67,2%); oito, C. glabrata (12,5%); cinco, C. krusei (7,8%); três, C. tropicalis (4,7%); e em três não foi possível determinar a espécie (4,7%). Anfotericina B e cetoconazol inibiram 94,9% dos isolados. Por outro lado, 55,9% e 54,2%, respectivamente, apresentaram resistência a itraconazol e fluconazol. As taxas de resistência a itraconazol e fluconazol de C. glabrata e C. albicans e também do fluconazol entre C. albicans e C. krusei apresentaram diferenças significativas (p < 0,05). Conclusão: Os dados demonstram a importância de se realizar a identificação completa e também o antifungigrama para amostras que apresentam infecção por leveduras...

Stereospecific metabolism of itraconazole by CYP3A4: dioxolane ring scission of azole antifungals.

Itraconazole (ITZ) is a mixture of four cis-stereoisomers that inhibit CYP3A4 potently and coordinate CYP3A4 heme via the triazole nitrogen. However, (2R,4S,2'R)-ITZ and (2R,4S,2'S)-ITZ also undergo stereoselective sequential metabolism by CYP3A4 at a site distant from the triazole ring to 3'-OH-ITZ, keto-ITZ, and N-desalkyl-ITZ. This stereoselective metabolism demonstrates specific interactions of ITZ within the CYP3A4 active site. To further investigate this process, the binding and metabolism of the four trans-ITZ stereoisomers by CYP3A4 were characterized. All four trans-ITZ stereoisomers were tight binding inhibitors of CYP3A4-mediated midazolam hydroxylation (IC(50) 16-26 nM), and each gave a type II spectrum upon binding to CYP3A4. However, instead of formation of 3'-OH-ITZ, they were oxidized at the dioxolane ring, leading to ring scission and formation of two new metabolites of ITZ. These two metabolites were also formed from the four cis-ITZ stereoisomers, although not as efficiently. The catalytic rates of dioxolane ring scission were similar to the dissociation rates of ITZ stereoisomers from CYP3A4, suggesting that the heme iron is reduced while the triazole moiety coordinates to it and no dissociation of ITZ is necessary before catalysis. The triazole containing metabolite [1-(2,4-dichlorophenyl)-2-(1H-1,2,4-triazol-1-yl)ethanone] also inhibited CYP3A4 (IC(50) >15 µM) and showed type II binding with CYP3A4. The dioxolane ring scission appears to be clinically relevant because this metabolite was detected in urine samples from subjects that had been administered the mixture of cis-ITZ isomers. These data suggest that the dioxolane ring scission is a metabolic pathway for drugs that contain this moiety.

Risk of azole-enhanced vincristine neurotoxicity in pediatric patients with hematological malignancies: old problem - new dilemma.

One of the most well-known drug interactions in pediatric oncology concerns the co-administration of itraconazole, an antifungal triazole, and vincristine, an antileukemic agent, which seems to enhance the risk of neurotoxicity of the latter, mediated through the cytochrome CYP450 enzyme system. The aim of this article is to review the metabolism of these two drugs, to analyze the published cases with severe triazole-enhanced vincristine neurotoxicity, to discuss the pathophysiological mechanisms of this adverse effect, and to contribute in understanding the differences in triazole-vincristine interaction severity.

Pharmacokinetic interaction of ketoconazole and itraconazole with ciprofloxacin.

The effect of the concomitant administration of the antifungal drugs ketoconazole (KTC) and itraconazole (ITC) on the pharmacokinetics of ciprofloxacin (CIP) following short- and long-term administration in mice was investigated. Animals received either a dose of CIP (20 mg/kg, i.p.), CIP (20 mg/kg, i.p.) together with KTC (50 mg/kg, p.o.) or CIP (20 mg/kg, i.p.) and ITC (30 mg/kg, p.o.). The same treatments were repeated for 7 days. Blood samples were collected up to 4 h following drug administration and two urine samples were collected at 2 h and 4 h after drug administration. CIP plasma concentrations were significantly higher in KTC- and ITC-treated groups compared with the corresponding control groups. The concomitant administration of KTC or ITC with CIP also significantly (p<0.05) increased C(max), t(1/2), MRT and AUC(0-infinity) with no change in T(max). CIP clearance was significantly reduced by both agents. KTC and ITC reduced CIP urinary excretion. This study suggests that an important pharmacokinetic interaction between CIP and KTC or ITC is likely to occur when either of the two antifungal drugs is administered concomitantly with CIP. The results may suggest possible reductions in total clearance of CIP, owing to inhibition of its renal tubular excretion by KTC and ITC.

Metabolic profiling of a potential antifungal drug, 3-(4-bromophenyl)-5-acetoxymethyl-2,5-dihydrofuran-2-one, in mouse urine using high-performance liquid chromatography with UV photodiode-array and mass spectrometric detection.

3-(4-bromophenyl)-5-acetyloxymethyl-2,5-dihydrofuran-2-one (LNO-18-22) is a representative member of a novel group of potential antifungal drugs, derived from a natural 3,5-disubstituted butenolide, (-)incrustoporine, as a lead structure. This lipophilic compound is characterized by high in vitro antifungal activity and low acute toxicity. For the purpose of in vivo studies, a new bioanalytical high-performance liquid chromatographic method with UV photodiode-array and mass spectrometric detection (HPLC-PDA-MS), involving a direct injection of diluted mouse urine was developed and used in the evaluation of the metabolic profiling of this drug candidate. The separation of LNO-18-22 and its phase I metabolites was performed in 37 min on a 125 mmx4 mm chromatographic column with Purospher RP-18e using an acetonitrile-water gradient elution. Scan mode of UV detection (195-380 nm) was employed for the identification of the parent compound and its biotransformation products in the biomatrix. Finally, the identity of LNO-18-22 and its metabolites was confirmed using HPLC-MS analyses of the eluate. These experiments demonstrated the power of a comprehensive analytical approach based on the combination of xenobiochemical methods and the results from tandem HPLC-PDA-MS (chromatographic behaviour, UV and MS spectra of native metabolites versus synthetic standards). The chemical structures of five phase I LNO-18-22 metabolites and one phase II metabolite were elucidated in the mouse urine, with two of these metabolites having very unexpected structures.

Candida urinary tract infections: treatment options.

Candiduria is a nonspecific finding that occurs with contamination of a urine sample, colonization of an indwelling catheter and/or the bladder, symptomatic cystitis and invasive upper tract infection. Most patients are colonized and do not require antifungal therapy. Removing predisposing factors, such as indwelling catheters and antibiotics, will clear candiduria in almost 50% of asymptomatic patients. For patients with symptomatic Candida urinary tract infections, a variety of treatment options are available. Fluconazole is the antifungal agent of choice, achieving high urine concentrations with the oral formulation. Rarely, amphotericin B or flucytosine are used. Newer azole agents and echinocandins are not recommended for the treatment of urinary tract infections since they fail to achieve adequate urine concentrations.

Disposition of caspofungin: role of distribution in determining pharmacokinetics in plasma.

The disposition of caspofungin, a parenteral antifungal drug, was investigated. Following a single, 1-h, intravenous infusion of 70 mg (200 microCi) of [(3)H]caspofungin to healthy men, plasma, urine, and feces were collected over 27 days in study A (n = 6) and plasma was collected over 26 weeks in study B (n = 7). Supportive data were obtained from a single-dose [(3)H]caspofungin tissue distribution study in rats (n = 3 animals/time point). Over 27 days in humans, 75.4% of radioactivity was recovered in urine (40.7%) and feces (34.4%). A long terminal phase (t(1/2) = 14.6 days) characterized much of the plasma drug profile of radioactivity, which remained quantifiable to 22.3 weeks. Mass balance calculations indicated that radioactivity in tissues peaked at 1.5 to 2 days at approximately 92% of the dose, and the rate of radioactivity excretion peaked at 6 to 7 days. Metabolism and excretion of caspofungin were very slow processes, and very little excretion or biotransformation occurred in the first 24 to 30 h postdose. Most of the area under the concentration-time curve of caspofungin was accounted for during this period, consistent with distribution-controlled clearance. The apparent distribution volume during this period indicated that this distribution process is uptake into tissue cells. Radioactivity was widely distributed in rats, with the highest concentrations in liver, kidney, lung, and spleen. Liver exhibited an extended uptake phase, peaking at 24 h with 35% of total dose in liver. The plasma profile of caspofungin is determined primarily by the rate of distribution of caspofungin from plasma into tissues.

Stripping voltammetric and polarographic techniques for the determination of anti-fungal ketoconazole on the mercury electrode.

The electroanalytical behaviour of ketoconazole in Britton-Robinson buffer is described. The reduction process on the hanging mercury drop electrode (HMDE) gives rise to one peak over -1.6 V (vs. Ag/AgCl/sat.KCl), within the pH range studied (4.7-9.6). The results showed that the reduction of ketoconazole is irreversible and the limiting current is adsorption controlled. The dependence of the peak current on the concentration was studied by means of different polarographic and voltammetric techniques. Using adsorptive stripping differential pulse voltammetry (AdS-DPV), the detection limit (DL) reached was 5.3 x 10(-11) mol l(-1). Two procedures, based on differential pulse polarography (DPP) and AdS-DPV in aqueous medium were developed for the determination of ketoconazole in a gel formulation and spiked urine samples, respectively.

Efficacy of a single intravenous dose of amphotericin B for Candida urinary tract infections: further favorable experience.

Studies in experimental animals and humans have shown that Amphotericin B (AmB) persists in urine for days to weeks after a single IV dose in levels that should inhibit candidal organisms and thereby obviate the need for frequent dosing. Including data from four previously described patients, we have now treated a total of 11 patients (12 episodes) with Candida urinary tract infections with single-dose AmB (six, Candida albicans; two, C. tropicalis; four, other nonalbicans Candida). The duration of candiduria prior to entry ranged from 18 to 180 days. Predisposing conditions included renal transplantation (1), diabetes mellitus (8), genitourinary stones (1) or anomalies (4), catheterization (2), and antibacterial therapy (11). A single patient was intolerant of AmB. Out of 11 evaluable candiduric episodes, eight resolved. Failure occurred in one patient with a chronic indwelling bladder catheter and in the allograft recipient. The data suggest that the sustained urinary excretion of AmB may permit successful single- or paucidose therapy of Candida urinary tract infections in some patients with a minimum of toxicity.

Pharmacokinetics and tissue distribution of a new partricin A derivative (N-dimethylaminoacetyl-partricin A 2-dimethylaminoethylamide diaspartate) in mice.

A single-dose trial in mice (1.25 mg/kg SPA-S-753 or 1 mg/kg amphotericin B [AmB] by intravenous route) was performed to study the pharmacokinetics, tissue distribution, and urinary excretion of a new polyene, SPA-S-753 (N-dimethylaminoacetyl-partricin A 2-dimethylaminoethylamide diaspartate), in comparison with AmB. Antibiotic concentrations were determined by microbiological assay (agar diffusion method). The elimination half-lives in serum were 15.1 and 19.8 h, respectively, for SPA-S-753 and AmB; the area under the curve from 0 to infinity values were 49.3 for SPA-S-753 and 23.6 microg. h/mL for AmB, because of the higher serum levels of SPA-S-753 found just after administration. The tissue concentrations of SPA-S-753 were lower than those of AmB in liver and lungs but higher in the kidneys. The urine concentrations of SPA-S-753 and the percent of the administered dose recovered from the urine were quite low in mice, whereas those of AmB were higher.

Adsorptive behavior and electrochemical determination of the anti-fungal agent ketoconazole.

The adsorptive properties and electrochemical behavior of ketoconazole, an oral anti-fungal agent, are demonstrated at a glassy carbon electrode. The adsorption of the compound obeys the Frumkin isotherm with an interaction factor (alpha) of 0.985 and adsorptive coefficient (beta) of 1.98 x 10(6) L mol(-1). The Gibbs energy of adsorption (deltaG) is -3.59 x 10(4) J mol(-1) at 25 degrees C. A very sensitive electroanalytical method has been developed for determination of the drug with a detection limit of 4.0 x 10(-11) mol L(-1). Relationships between stripping current and concentration of ketoconazole were linear in the range 10(-6)-10(-10) mol L(-1) with different preconcentration periods. The method has been used to measure the ketoconazole content of tablets.