Determination of plasma unbound fraction of voriconazole in patients treated with a prophylactic or a curative treatment

Postantifungal Effect of Antifungal Drugs against Candida: What Do We Know and How Can We Apply This Knowledge in the Clinical Setting?

The study of the pharmacological properties of an antifungal agent integrates the drug pharmacokinetics, the fungal growth inhibition, the fungicidal effect and the postantifungal activity, laying the basis to guide optimal dosing regimen selection. The current manuscript reviews concepts regarding the postantifungal effect (PAFE) of the main classes of drugs used to treat Candida infections or candidiasis. The existence of PAFE and its magnitude are highly dependent on both the fungal species and the class of the antifungal agent. Therefore, the aim of this article was to compile the information described in the literature concerning the PAFE of polyenes, azoles and echinocandins against the Candida species of medical interest. In addition, the mechanisms involved in these phenomena, methods of study, and finally, the clinical applicability of these studies relating to the design of dosing regimens were reviewed and discussed. Additionally, different factors that could determine the variability in the PAFE were described. Most PAFE studies were conducted in vitro, and a scarcity of PAFE studies in animal models was observed. It can be stated that the echinocandins cause the most prolonged PAFE, followed by polyenes and azoles. In the case of the triazoles, it is worth noting the inconsistency found between in vitro and in vivo studies.

The Impact of Plasma Protein Binding Characteristics and Unbound Concentration of Voriconazole on Its Adverse Drug Reactions

This study investigated voriconazole (VRC) unbound plasma concentration and its relationship with adverse drug reactions (ADRs) in patients with malignant hematologic disease. Plasma samples were collected from patients or spiked in vitro. A time-saving rapid equilibrium dialysis assay was used for the separation of unbound and bound VRC, following a high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) analysis method for drug concentration detection. Liver function and treatment details were collected from the electronic medical records of patients. Protein concentration was determined according to instructions. VRC plasma protein binding rate (PPB) in patient is significantly higher [69.5 ± 6.2%] than that in in-vitro samples, influenced by total drug concentration (C_t), plasma protein concentration, and protein type. The α1-acid glycogen (AAG) has the highest affinity with VRC. Relationship between total PPB of VRC with PPB of individual protein is not a simple addition, but a compressive combination. Unbound drug concentration (C_u) of VRC shows significant relationships with C_t, protein concentration, AST level, metabolism type of CYP2C19 and co-administration of high PPB medicines. Unbound plasma concentration of VRC shows a more sensitive relationship with ADRs than C_t.

A rapid ultra-performance LC-MS/MS assay for determination of serum unbound fraction of voriconazole in cancer patients

BACKGROUND

Voriconazole (VOR), an antifungal agent, is clinically monitored to guide therapeutic dosing and avoid toxicity. It is believed that measurement of serum unbound VOR provides more accurate information, especially in hypoalbuminemia patients. We developed and validated an accurate, simple and fast test with ultrafiltration and ultra-performance liquid chromatography (UPLC)-tandem mass spectrometry (MS/MS) to measure unbound VOR in human serum.

METHODS

The Agilent UPLC system coupled with a SCIEX QTRAP4000 MS with a positive ionization mode was developed and validated for VOR analysis.

RESULTS

A good linearity was demonstrated from 0.02 to 2.5 μg/ml for unbound VOR (r² = 0.9969). The within-run and between-run accuracy and precision was <5% and < 6%. The levels of total VOR were well correlated with reference laboratory results. Serum unbound VOR levels were correlated with the total VOR levels (r = 0.78, p < 0.0001). There was a reverse correlation between unbound VOR fractions and plasma albumin levels (p < 0.05). In hypoalbuminemia patients, the unbound VOR levels were increased to a higher degree than total VOR.

CONCLUSION

This assay is suitable for monitoring both unbound and bound VOR in cancer patients especially in those with hypoalbuminemia in clinical laboratories. Measurement of unbound VOR offers a better approach in prediction of VOR toxicity.

Is the unbound concentration of atazanavir of interest in therapeutic drug monitoring?

To date, therapeutic drug monitoring (TDM) is carried out with antiretrovirals and is usually based on total concentrations (C_t ). However, for some patients, TDM does not reflect efficacy or the avoidance of toxicity as is the case for atazanavir (ATV), a HIV protease inhibitor. As the unbound concentration (C_u ) is the pharmacological active form, the aim of the study was to evaluate the value of C_u and the unbound fraction (f_u , f_u = C_u /C_t ) for the TDM of ATV. The variability of C_u and the corresponding f_u of ATV was explored in 43 patients treated with ATV for an average of 13.5 months. C_u was determined by coupling ultrafiltration and liquid chromatography. As ATV is highly bound to alpha-1 acid glycoprotein (AAG), the correlation between f_u and AAG was also evaluated. The viral load was monitored to evaluate the patients' virologic response, while total plasma bilirubin and unconjugated plasma bilirubin were used as biomarkers of ATV toxicity. Median trough C_u and C_t were 37.9 μg/L (Interquartile range (IQR) 20.6-94.9 μg/L) and 628.6 μg/L (IQR 362.7-1078.1 μg/L), respectively. f_u , C_u and C_t showed high variability, but the f_u variability was not correlated with the AAG level. The unbound concentration and fraction were unrelated to the virologic response (P = 0.21 and P = 0.65 for C_u and f_u , respectively) nor to the unconjugated bilirubin (Pearson correlation coefficient (ρ), ρ = 0.22; P = 0.17 for C_u ). Neither total nor unbound concentrations of ATV fully explained hyperbilirubinaemia or virologic failure. From this study, we conclude that unbound ATV did not appear to be more relevant than C_t .

Impact of hypoalbuminemia on voriconazole pharmacokinetics in critically ill adult patients

Setting the adequate dose for voriconazole is challenging due to its variable pharmacokinetics. We investigated the impact of hypoalbuminemia (<35 g/liter) on voriconazole pharmacokinetics in adult intensive care unit (ICU) patients treated with voriconazole (20 samples in 13 patients) as well as in plasma samples from ICU patients that had been spiked with voriconazole at concentrations of 1.5 mg/liter, 2.9 mg/liter, and 9.0 mg/liter (66 samples from 22 patients). Plasma albumin concentrations ranged from 13.8 to 38.7 g/liter. Total voriconazole concentrations in adult ICU patients treated with voriconazole ranged from 0.5 to 8.7 mg/liter. Unbound and bound voriconazole concentrations were separated using high-throughput equilibrium dialysis followed by liquid chromatography-tandem mass spectrometry (LC-MSMS). Multivariate analysis revealed a positive relationship between voriconazole plasma protein binding and plasma albumin concentrations (P < 0.001), indicating higher unbound voriconazole concentrations with decreasing albumin concentrations. The correlation is more pronounced in the presence of elevated bilirubin concentrations (P = 0.05). We therefore propose to adjust the measured total voriconazole concentrations in patients with abnormal plasma albumin and total serum bilirubin plasma concentrations who show adverse events potentially related to voriconazole via a formula that we developed. Assuming 50% protein binding on average and an upper limit of 5.5 mg/liter for total voriconazole concentrations, the upper limit for unbound voriconazole concentrations is 2.75 mg/liter. Alterations in voriconazole unbound concentrations caused by hypoalbuminemia and/or elevated bilirubin plasma concentrations cannot be countered immediately, due to the adult saturated hepatic metabolism. Consequently, increased unbound voriconazole concentrations can possibly cause adverse events, even when total voriconazole concentrations are within the reference range.