A new PK/PD target for assessing efficacy of micafungin against Candida parapsilosis

BACKGROUND

Pharmacokinetic/pharmacodynamic (PK/PD) targets of echinocandins failed to support current clinical breakpoints of Candida parapsilosis as the PTA is low for susceptible isolates despite the good clinical efficacy of echinocandins against these infections. We therefore investigated the effect of micafungin against C. parapsilosis using an in vitro PK/PD in the presence of 10% human serum.

METHODS

Three susceptible (MIC = 0.5-2 mg/L) and one resistant (MIC > 8 mg/L) C. parapsilosis sensu stricto isolates were tested at two different inocula (104 and 103 cfu/mL) simulating micafungin human exposures in RPMI and in RPMI + 10% pooled human serum. The exposure-effect relationship tAUC0-24/MIC was described and different PK/PD targets were determined in order to calculate the PTA for the standard 100 mg IV q24h dose.

RESULTS

A maximal effect was found at fCmax ≥ 4 mg/L in RPMI and tCmax ≥ 64 mg/L (fCmax = 0.08 mg/L) in the presence of serum for which in vitro PK/PD targets were 50 times lower. Stasis in the presence of serum was found at 272-240 tAUC0-24/MIC, close to the clinical PK/PD target (285 tAUC/MIC), validating the in vitro model. However, the PTA was low for susceptible isolates with EUCAST/CLSI MICs ≤ 2 mg/L. Among the different PK/PD targets investigated, the PK/PD target 28 tAUC/MIC associated with 10% of maximal effect with the low inoculum resulted in PTAs ≥ 95% for susceptible isolates with EUCAST/CLSI MICs ≤ 2 mg/L.

CONCLUSIONS

A new PK/PD target was found for micafungin and C. parapsilosis that supports the current clinical breakpoint. This target could be used for assessing echinocandin efficacy against C. parapsilosis.

Absence of Clinically Meaningful Drug-Drug Interactions with Rezafungin: Outcome of Investigations

Rezafungin is a novel once-weekly echinocandin for intravenous injection currently in development for the treatment of Candida infections and the prevention of Candida, Aspergillus, and Pneumocystis infections in allogeneic blood and marrow transplant recipients. While in vitro data indicated that rezafungin exposure was unlikely to be affected by commonly prescribed medicines, interactions resulting in the altered systemic exposure of some drugs coadministered with rezafungin could not be excluded. Two phase 1 open label crossover studies, conducted in healthy subjects, examined drug interactions between rezafungin and multiple drug probe cytochrome P450 (CYP) substrates and/or transporter proteins, immunosuppressants, and cancer therapies. Statistical analysis compared the outcomes for drugs coadministered with rezafungin to those for the drugs administered alone. The geometric mean ratio was reported, and a default 90% confidence interval (CI) no-effect equivalence range of 80 to 125% was used for the maximal plasma concentration (Cmax), the area under the curve from time zero to the final sampling time point (AUC0-t), and the AUC from time zero to infinity (AUC0-∞). Most probes and concomitant drugs were within the equivalence range. For tacrolimus, ibrutinib, mycophenolic acid, and venetoclax, the AUC or Cmax was reduced (10 to 19%), with lower bounds of the 90% CI values falling outside the no-effect range. The rosuvastatin AUC and Cmax and the repaglinide AUC0-∞ were increased (12 to 16%), with the 90% CI being marginally above the upper bound. Overall, the in vitro and in vivo data demonstrated a low drug interaction potential with rezafungin via CYP substrate/transporter pathways and commonly prescribed comedications, suggesting that coadministration was unlikely to result in clinically significant effects. Treatment-emergent adverse events were typically mild, and rezafungin was generally well tolerated. IMPORTANCE Antifungal agents used to treat life-threatening infections are often associated with severe drug-drug interactions (DDIs) that may limit their usefulness. Rezafungin, a newly approved once-weekly echinocandin, has been shown to be free of DDIs based on extensive nonclinical and clinical testing described in this study.

A protocol for an international, multicentre pharmacokinetic study for Screening Antifungal Exposure in Intensive Care Units: The SAFE-ICU study

Objective

To describe whether contemporary dosing of antifungal drugs achieves therapeutic exposures in critically ill patients that are associated with optimal outcomes. Adequate antifungal therapy is a key determinant of survival of critically ill patients with fungal infections. Critical illness can alter an antifungal agents' pharmacokinetics, increasing the risk of inappropriate antifungal exposure that may lead to treatment failure and/or toxicity.

Design setting and participants

This international, multicentre, observational pharmacokinetic study will comprise adult critically ill patients prescribed antifungal agents including fluconazole, voriconazole, posaconazole, isavuconazole, caspofungin, micafungin, anidulafungin, and amphotericin B for the treatment or prophylaxis of invasive fungal disease. A minimum of 12 patients are targeted for enrolment for each antifungal agent, across 12 countries and 30 intensive care units to perform descriptive pharmacokinetics. Pharmacokinetic sampling will occur during two dosing intervals (occasions): firstly, between days 1 and 3, and secondly, between days 4 and 7 of the antifungal course, collecting three samples per occasion. Patients' demographic and clinical data will be collected.

Main outcome measures

The primary endpoint of the study is attainment of pharmacokinetic/pharmacodynamic target exposures that are associated with optimal efficacy. Thirty-day mortality will also be measured.

Results and conclusions

This study will describe whether contemporary antifungal drug dosing achieves drug exposures associated with optimal outcomes. Data will also be used for the development of antifungal dosing algorithms for critically ill patients. Optimised drug dosing should be considered a priority for improving clinical outcomes for critically ill patients with fungal infections.

Population Pharmacokinetic Model and Optimal Sampling Strategies for Micafungin in Critically Ill Patients Diagnosed with Invasive Candidiasis

Candida bloodstream infections are associated with high attributable mortality, where early initiation of adequate antifungal therapy is important to increase survival in critically ill patients. The exposure variability of micafungin, a first-line agent used for the treatment of invasive candidiasis, in critically ill patients is significant, potentially resulting in underexposure in a substantial portion of these patients. The objective of this study was to develop a population pharmacokinetic model including appropriate sampling strategies for assessing micafungin drug exposure in critically ill patients to support adequate area under the concentration-time curve (AUC) determination. A two-compartment pharmacokinetic model was developed using data from intensive care unit (ICU) patients (n = 19), with the following parameters: total body clearance (CL), volume of distribution of the central compartment (V1), inter-compartmental clearance (CL12), and volume of distribution of the peripheral compartment (V2). The final model was evaluated with bootstrap analysis and the goodness-of-fit plots for the population and individual predicted micafungin plasma concentrations. Optimal sampling strategies (with sampling every hour, 24 h per day) were developed with 1- and 2-point sampling schemes. Final model parameters (±SD) were: CL = 1.03 (0.37) (L/h/1.85 m²), V1 = 0.17 (0.07) (L/kg LBMc), CL12 = 1.80 (4.07) (L/h/1.85 m²), and V2 = 0.12 (0.06) (L/kg LBMc). Sampling strategies with acceptable accuracy and precision were developed to determine the micafungin AUC. The developed model with optimal sampling procedures provides the opportunity to achieve quick optimization of the micafungin exposure from a single blood sample using Bayesian software and may be helpful in guiding early dose decision-making.

Therapeutic Drug Monitoring of the Echinocandin Antifungal Agents: Is There a Role in Clinical Practice? A Position Statement of the Anti-Infective Drugs Committee of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology

PURPOSE

Reduced exposure to echinocandins has been reported in specific patient populations, such as critically ill patients; however, fixed dosing strategies are still used. The present review examines the accumulated evidence supporting echinocandin therapeutic drug monitoring (TDM) and summarizes available assays and sampling strategies.

METHODS

A literature search was conducted using PubMed in December 2020, with search terms such as echinocandins, anidulafungin, caspofungin, micafungin, or rezafungin with pharmacology, pharmacokinetics (PKs), pharmacodynamics (PDs), drug-drug interactions, TDM, resistance, drug susceptibility testing, toxicity, adverse drug reactions, bioanalysis, chromatography, and mass spectrometry. Data on PD/PD (PK/PD) outcome markers, drug resistance, PK variability, drug-drug interactions, assays, and TDM sampling strategies were summarized.

RESULTS

Echinocandins demonstrate drug exposure-efficacy relationships, and maximum concentration/minimal inhibitory concentration ratio (Cmax/MIC) and area under the concentration-time curve/MIC ratio (AUC/MIC) are proposed PK/PD markers for clinical response. The relationship between drug exposure and toxicity remains poorly clarified. TDM could be valuable in patients at risk of low drug exposure, such as those with critical illness and/or obesity. TDM of echinocandins may also be useful in patients with moderate liver impairment, drug-drug interactions, hypoalbuminemia, and those undergoing extracorporeal membrane oxygenation, as these conditions are associated with altered exposure to caspofungin and/or micafungin. Assays are available to measure anidulafungin, micafungin, and caspofungin concentrations. A limited-sampling strategy for anidulafungin has been reported.

CONCLUSIONS

Echinocandin TDM should be considered in patients at known risk of suboptimal drug exposure. However, for implementing TDM, clinical validation of PK/PD targets is needed.

Use and outcome of empiric echinocandins in critically ill patients

BACKGROUND

Echinocandins are recommended as a first-line empiric treatment for fungal infections of patients in an intensive care unit (ICU) with critical illness. The primary aim of the study was to compare outcomes among ICU patients treated with empiric anidulafungin (ANI), caspofungin (CASPO), or micafungin (MICA).

METHODS

A retrospective cohort study in a mixed adult ICU. Patient demographics, reason for ICU admission, ICU risk scores and organ support therapies were analyzed. Outcome parameters included ICU and hospital stay, 30-day mortality and 1-year mortality.

RESULTS

Empiric echinocandin therapy was given to 367 patients (ANI; 73 patients, CASPO; 84 patients, and MICA; 210 patients) with a median duration of 3 days in an ICU. Patient median age was 60.7 years. As a first-line therapy, 52% of patients received fluconazole. Positive Candida cultures were found in the following samples: blood, 16 (4.4%); central line, 27 (7.4%); deep site, 92 (25.1%). Median ICU stay (ANI 6.4 days, CASPO 5.3 days, MICA 8.1 days), hospital stay (ANI 33 days, CASPO 30 days, MICA 30 days), 30-day mortality (ANI 27%, CASPO 32%, MICA 32%), and 1-year mortality (ANI 33%, CASPO 44%, MICA 45%) did not differ between the groups . The cost of antifungal therapy during the ICU period was similar in the three echinocandin groups (ANI; €1 872, CASPO; €1 799, and MICA; €1783).

CONCLUSION

Our results show that ICU, hospital stay, and mortality (hospital, 30-day and 1-year) did not differ among patients with empiric anidulafungin, caspofungin, or micafungin treatment in a mixed adult ICU.

Penetration of echinocandins into wound secretion of critically ill patients

Purpose

Wound infections caused by Candida are life-threatening and difficult to treat. Echinocandins are highly effective against Candida species and recommended for treatment of invasive candidiasis. As penetration of echinocandins into wounds is largely unknown, we measured the concentrations of the echinocandins anidulafungin (AFG), micafungin (MFG), and caspofungin (CAS) in wound secretion (WS) and in plasma of critically ill patients.

Methods

We included critically ill adults with an indwelling wound drainage or undergoing vacuum-assisted closure therapy, who were treated with an echinocandin for suspected or proven invasive fungal infection. Concentrations were measured by liquid chromatography with UV (AFG and MFG) or tandem mass spectrometry detection (CAS).

Results

Twenty-one patients were enrolled. From eight patients, serial WS samples and simultaneous plasma samples were obtained within a dosage interval. AFG concentrations in WS amounted to < 0.025–2.25 mg/L, MFG concentrations were 0.025–2.53 mg/L, and CAS achieved concentrations of 0.18–4.04 mg/L. Concentrations in WS were significantly lower than the simultaneous plasma concentrations and below the MIC values of some relevant pathogens.

Conclusion

Echinocandin penetration into WS displays a high inter-individual variability. In WS of some of the patients, concentrations may be sub-therapeutic. However, the relevance of sub-therapeutic concentrations is unknown as no correlation has been established between concentration data and clinical outcome. Nevertheless, in the absence of clinical outcome studies, our data do not support the use of echinocandins at standard doses for the treatment of fungal wound infections, but underline the pivotal role of surgical debridement.

Supplementary Information

The online version contains supplementary material available at 10.1007/s15010-021-01604-x.