Role of therapeutic drug monitoring of voriconazole in the treatment of invasive fungal infections

[Clinical Analysis of Voriconazole Concentrations in Cerebrospinal Fluid and Blood in Patients with Ryptococcal Meningitis]

Objective

To investigate the concentrations of voriconazole (VCZ) in the central nervous system (CNS) of patients with cryptococcal meningitis and the relationship thereof.

Methods

We retrospectively analyzed the trough concentration of VCZ in the cerebrospinal fluid (CSF) and the blood of 25 adult patients who had cryptococcal meningitis, and who were not infected with HIV. We also examined patient-level characteristics that could contribute to the differences in CSF/plasma VCZ concentration ratio.

Results

The trough concentration of VCZ in plasma ranged from 0.38 to 8.56 mg/L, and the median (P 25, P 75) was 1.81 (1.40, 3.84) mg/L. The trough concentration of VCZ in CSF ranged from 0.17 to 3.92 mg/L, and the median (P 25, P 75) was 1.02 (0.54, 1.84) mg/L. The CSF VCZ trough concentration showed a slight negative correlation with the nucleated cell counts in CSF, but the correlation was not statistically significant ( r=-0.377, P=0.063). There was a positive correlation between VCZ concentrations in CSF and that in the plasma ( r=0.736, P<0.001), and the median (P 25, P 75) CSF/plasma ratio was 0.43 (0.34, 0.68). The CSF/plasma ratio did not statistically correlate with age, body surface area (BSA), radiology changes (hydrocephalus), or intracranial pressure.

Conclusion

There is a positive correlation between VCZ concentration in CSF and VCZ concentration in the plasma, and no influencing factors of CSF/plasma ratio were found.

Evaluation of Voriconazole CYP2C19 Phenotype-Guided Dose Adjustments by Physiologically Based Pharmacokinetic Modeling

BACKGROUND AND OBJECTIVES

Controversy exists regarding dose adjustment in patients treated with voriconazole due to the severity of the infections for which it is prescribed. The Dutch Pharmacogenetics Working Group (DPWG) recommends a 50% dose increase or decrease for cytochrome P450 (CYP) 2C19 ultrarapid (UM) or poor (PM) metabolizers, respectively. In contrast, for the previous phenotypes, the Clinical Pharmacogenetics Implementation Consortium (CPIC) voriconazole guideline only recommends a change of treatment. Based on observed data from single-dose bioequivalence studies and steady-state observed concentrations, we aimed to investigate voriconazole dose adjustments by means of physiologically based pharmacokinetic (PBPK) modeling.

METHODS

PBPK modeling was used to optimize voriconazole single-dose models for each CYP2C19 phenotype, which were extrapolated to steady state and evaluated for concordance with the therapeutic range of voriconazole. Based on optimized models, dose adjustments were evaluated for better adjustment to the therapeutic range.

RESULTS

Our models suggest that the standard dose may only be appropriate for normal metabolizers (NM), although they would benefit from a 50-100% loading dose increase. Intermediate metabolizers (IMs) and PMs required a daily dose reduction of 50 and 75%, respectively. Rapid metabolizers (RMs) and UMs required a daily dose increase of 100% and 300%, respectively.

CONCLUSION

The prescription of voriconazole in clinical practice should be personalized according to the CYP2C19 phenotype, followed by therapeutic drug monitoring of plasma concentrations to guide dose adjustment.

Clinical Pharmacokinetics of Second-Generation Triazoles for the Treatment of Invasive Aspergillosis and Candidiasis

Second-generation triazoles were developed in response to the quest for more efficacious and safer therapeutic options for the treatment of severe systemic aspergillosis and candidiasis. These agents include voriconazole, posaconazole, isavuconazole, and ravuconazole. The aim of this review was to present and compare the pharmacokinetic characteristics of second-generation triazoles for the treatment of invasive aspergillosis and candidiasis, emphasizing their clinical implications. The MEDLINE, Scopus, EBSCO, Google Scholar, and SCIndeks databases were searched using advanced search options, including the names of second-generation triazoles and pharmacokinetic terms as keywords. The intravenous administration of voriconazole, posaconazole, and isavuconazole results in stable pharmacokinetics of these drugs, with mostly predictable variations influenced by common and usually known factors in routine clinical settings. The high oral bioavailability of isavuconazole and, to some extent, voriconazole makes them suitable for intravenous-to-oral switch strategies. Except for intravenous voriconazole (due to the accumulation of the toxic vehicle hydroxypropyl betadex), dose reduction of second-generation triazoles is not needed in patients with renal failure; patients with hepatic insufficiency require dose reduction only in advanced disease stages. The introduction of therapeutic drug monitoring could aid attempts to optimize the blood concentrations of triazoles and other drugs that are known to or that possibly interact, thus increasing treatment efficacy and safety. There is a need for new studies that are designed to provide useful data on second-generation triazole pharmacokinetics, particularly in special circumstances such as central nervous system and ocular infections, infections in newborns and infants, and in subjects with genetic polymorphisms of metabolizing enzymes.

Interpersonal Factors in the Pharmacokinetics and Pharmacodynamics of Voriconazole: Are CYP2C19 Genotypes Enough for Us to Make a Clinical Decision?

Background:

Invasive mycoses are serious infections with high mortality and increasing inci-dence. Voriconazole, an important drug to treat invasive mycosis, is metabolized mainly by the cytochrome P450 family 2 subfamily C member 19 enzyme (CYP2C19) and is affected by the genotypes of CYP2C19.

Objective:

We reviewed studies on how genotypes affect the pharmacokinetics and pharmacodynamics of voriconazole, and attempted to determine a method to decide on dosage adjustments based on genotypes, after which, the main characteristic of voriconazole was clarified in details. The pharmacokinetics of voriconazole are influenced by various inter and intrapersonal factors, and for certain populations, such as geriatric patients and pediatric patients, these influences must be considered. CYP2C19 genotype represents the main part of the interpersonal variability related to voriconazole blood concentrations. Thus monitoring the concentration of voriconazole is needed in clinical scenarios to minimize the negative influences of inter and intrapersonal factors. Several studies provided evidence on the stable trough concentration range from 1-2 to 4-6 mg/L, which was combined to consider the efficacy and toxicity. However, the therapeutic drug concentration needs to be narrowed down and evaluated by large-scale clinical trials.

Conclusion:

Though there is insufficient evidence on the relationship between CYP2C19 genotypes and clinical outcomes, there is a great potential for the initial voriconazole dose selection to be guided by the CYP2C19 genotype. Finally, voriconazole therapeutic drug monitoring is essential to provide patient-specific dosing recommendations, leading to more effective anti-fungal regimens to increase clinical effica-cy and reduce adverse drug reactions.

Revolutionizing Therapeutic Drug Monitoring with the Use of Interstitial Fluid and Microneedles Technology

While therapeutic drug monitoring (TDM) that uses blood as the biological matrix is the traditional gold standard, this practice may be impossible, impractical, or unethical for some patient populations (e.g., elderly, pediatric, anemic) and those with fragile veins. In the context of finding an alternative biological matrix for TDM, this manuscript will provide a qualitative review on: (1) the principles of TDM; (2) alternative matrices for TDM; (3) current evidence supporting the use of interstitial fluid (ISF) for TDM in clinical models; (4) the use of microneedle technologies, which is potentially minimally invasive and pain-free, for the collection of ISF; and (5) future directions. The current state of knowledge on the use of ISF for TDM in humans is still limited. A thorough literature review indicates that only a few drug classes have been investigated (i.e., anti-infectives, anticonvulsants, and miscellaneous other agents). Studies have successfully demonstrated techniques for ISF extraction from the skin but have failed to demonstrate commercial feasibility of ISF extraction followed by analysis of its content outside the ISF-collecting microneedle device. In contrast, microneedle-integrated biosensors built to extract ISF and perform the biomolecule analysis on-device, with a key feature of not needing to transfer ISF to a separate instrument, have yielded promising results that need to be validated in pre-clinical and clinical studies. The most promising applications for microneedle-integrated biosensors is continuous monitoring of biomolecules from the skin's ISF. Conducting TDM using ISF is at the stage where its clinical utility should be investigated. Based on the advancements described in the current review, the immediate future direction for this area of research is to establish the suitability of using ISF for TDM in human models for drugs that have been found suitable in pre-clinical experiments.

Comparison of clinical pharmacology of voriconazole and posaconazole

Despite greater knowledge and possibilities in pharmacotherapy, fungal infections remain a challenge for clinicians. As the population of immunocompromised patients and those treated for their hematologic ailments increases, the number of fungal infections grows too. This is why there is still a quest for new antifungal drugs as well as for optimization of pharmacotherapy with already registered pharmaceutics.

Voriconazole and posaconazole are broad-spectrum, new generation, triazole antifungal agents. The drugs are used in the pharmacotherapy of invasive aspergillosis, Candida and Fusarium infections. Voriconazole is also used in infections caused by Scedosporium. Posaconazole is used in the treatment of coccidioidomycosis and chromoblastomycosis. Besides some similarities, the two mentioned drugs also show differences in therapeutic indications, pharmacokinetics (mainly absorption and metabolism), frequency and severity of adverse drug reactions, drug–drug interactions and dosage. As both of the drugs are used in the treatment of invasive fungal infections in adults and children, detailed knowledge of the clinical pharmacology of antifungal agents is the main factor in pharmacotherapy optimization in treatment of fungal infections.

The goal of the article is to present and compare the clinical pharmacology of voriconazole and posaconazole as well as to point out the indications and contraindications of using the drugs, determine factors influencing their pharmacotherapy, and provide information that might be helpful in the treatment of fungal infections.