Hepatobiliary excretion of fluconazole and its interaction with cyclosporin A in rat blood and bile using microdialysis

Effect of Efflux Transporter Inhibition on the Distribution of Fluconazole in the Rat Brain

Multidrug resistance-associated proteins (MRPs) and organic anion transporters (OATs) are expressed on the blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCSFB), preventing the entry of or the pumping out of numerous molecules. Fluconazole is widely used to treat fungal meningoencephalitis. The effect of these transporters on the distribution of fluconazole in the brain is unclear. We used microdialysis to compare the distribution of fluconazole in the rat brain with and without co-administration of probenecid, a MRP and OAT inhibitor. Additionally, we also observed the difference in fluconazole distribution between the two barriers. The results showed that probenecid increased the penetration of fluconazole into the BBB but did not alter the penetration of fluconazole into the BCSFB of rats. The penetration of the BBB and BCSFB by fluconazole did not statistically differ according to physiological condition. These results demonstrate that transporters that can be inhibited by probenecid may be involved in fluconazole resistance at the BBB and provide a laboratory basis for predicting brain extracellular fluid (ECF) concentration using the cerebrospinal fluid (CSF) concentration of fluconazole.

Comparison of fluconazole renal penetration levels in healthy and Candida albicans-infected Wistar rats

The aims of this study were to evaluate free levels of fluconazole (FCZ) in the kidneys of healthy and Candida albicans-infected Wistar rats using microdialysis and to establish the relationship between free renal and total plasma levels under both conditions. Microdialysis recovery rates were determined in vitro by dialysis, and retrodialysis recovery rates were determined in vivo by retrodialysis. The recovery rate was around 50%, independent of the method, drug concentration, or condition (in vitro or in vivo) used. FCZ kidney penetration in healthy and infected rats was investigated after the administration of 10 mg/kg of body weight intravenously (i.v.) or 50 mg/kg orally (n = 6/group) and blood and microdialysate sample harvesting at predetermined time points up to 24 and 18 h, respectively. There were no statistical differences between the area under the free concentration-time curve (AUC(0-∞)) values in plasma and in tissue for either healthy or infected groups for the same dose regimen investigated. The antifungal tissue penetrations were similar for both doses and under all conditions investigated (ranging from 0.77 to 0.84). The unbound fraction of FCZ was concentration independent (86.0% ± 2.0%), allowing the prediction of free renal levels using pharmacokinetic parameters obtained from total plasma fitting. The results showed that free renal and free plasma levels are similar in healthy and systemically C. albicans-infected rats. Therefore, free plasma levels are a good surrogate to estimate free FCZ renal concentrations in systemic candidiasis and can be used to optimize dosing regimens for this drug.

The pharmacokinetics of fluconazole in healthy Chinese adult volunteers: influence of ethnicity and gender

OBJECTIVE

The purpose of the present study was to investigate and compare the influence of ethnicity (including Han, Mongolian, Korean, Hui and Uygur) and gender on the pharmacokinetics of fluconazole in healthy adult volunteers after administration of 200-mg fluconazole tablet.

METHODS

Ten healthy subjects (five males and five females) of each ethnicity were recruited and given a single 200-mg dose of fluconazole in tablet form. Blood samples were obtained before dosing and at various predetermined time points after administration up to 96 h. Drug levels were measured by high-performance liquid chromatography. The blood concentration-time profiles were analyzed using a non-compartmental approach to estimate the absorption parameters (AUC((0-96)), C(max) and t(max)), the distribution parameter (V(d)) and the disposition parameters (t(1/2) and CL).

RESULTS

Ethnicity did not affect the parameter estimates, but gender did. However, the gender differences in pharmacokinetic parameter could be accounted for by differences in weight. There was a high linear correlation between weight and ln C(max), ln AUC (ln means natural logarithmic transformation), V(d) and CL.

CONCLUSIONS

Ethnicity (Chinese Han, Mongolian, Korean, Hui and Uygur) influences the pharmacokinetics of fluconazole tablet. However, there were statistically significant gender differences in AUC, C(max), V(d) and CL. But these could be accounted for by weight differences. If fluconazole dose-adjustment is deemed necessary, this can be done on a weight basis rather than gender basis.

Human pharmacogenomic variations and their implications for antifungal efficacy

Pharmacogenomics is defined as the study of the impacts of heritable traits on pharmacology and toxicology. Candidate genes with potential pharmacogenomic importance include drug transporters involved in absorption and excretion, phase I enzymes (e.g., cytochrome P450-dependent mixed-function oxidases) and phase II enzymes (e.g., glucuronosyltransferases) contributing to metabolism, and those molecules (e.g., albumin, A1-acid glycoprotein, and lipoproteins) involved in the distribution of antifungal compounds. By using the tools of population genetics to define interindividual differences in drug absorption, distribution, metabolism, and excretion, pharmacogenomic models for genetic variations in antifungal pharmacokinetics can be derived. Pharmacogenomic factors may become especially important in the treatment of immunocompromised patients or those with persistent or refractory mycoses that cannot be explained by elevated MICs and where rational dosage optimization of the antifungal agent may be particularly critical. Pharmacogenomics has the potential to shift the paradigm of therapy and to improve the selection of antifungal compounds and adjustment of dosage based upon individual variations in drug absorption, metabolism, and excretion.

Biliary candida infections in primary sclerosing cholangitis

BACKGROUND/AIMS

Patients with Primary Sclerosing Cholangitis (PSC) frequently develop dominant stenoses of the bile ducts and bacterial infections represent a major problem in such patients. In the present study, the role of fungal infections of the bile ducts has been evaluated.

METHODS

In a prospective non-randomized trial, in 67 consecutive patients with PSC, 148 bile samples, each taken at one endoscopic examination, were microbiologically analysed.

RESULTS

Candida species were found in 8/67 patients whereas Aspergillus was not detected. Seven patients with biliary Candida had a dominant stenosis and one had a wide papillotomy with chronic ascending cholangitis. Altogether 7/49 of patients with dominant stenosis and 1/18 of patients without dominant stenosis had Candida in their bile. All patients with biliary Candida intermittently had received antibiotics and had advanced disease with cholestasis. Candida disappeared spontaneously in 2/7 patients, cleared after antifungal treatment in 2, and persisted in 3 patients. Patients with biliary Candida had more severe cholangitis with higher CRP and serum bilirubin compared to those without Candida infection.

CONCLUSIONS

This is the first report on the identification of Candida species in the bile of patients with PSC. Apart from bacterial also fungal infection of the bile ducts should be considered in the treatment of such patients.

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.