Population Pharmacokinetics of Anidulafungin in Critically Ill Patients

Echinocandins Pharmacokinetics: A Comprehensive Review of Micafungin, Caspofungin, Anidulafungin, and Rezafungin Population Pharmacokinetic Models and Dose Optimization in Special Populations

In recent years, many population pharmacokinetic (popPK) models have been developed for echinocandins to better understand the pharmacokinetics (PK) of these antifungals. This comprehensive review aimed to summarize popPK models of echinocandins (micafungin, caspofungin, anidulafungin, and rezafungin), by focusing on dosage optimization to maximize the probability of attaining the PK/PD target proposed in special populations. A search in PubMed, Embase, Web of Science, and Scopus, supplemented by the bibliography of relevant articles, was conducted from inception to March 2024, including both observational and prospective trials. A total of 1126 articles were identified, 47 of them were included in the review (22 for micafungin, 13 for caspofungin, 9 for anidulafungin, and 3 for rezafungin). A two-compartment model was more frequently used to describe the PK parameters of echinocandin (78.7% of developed models), although more complex structural models with three and four compartments have also been developed. The covariates to estimate the PK parameters such as clearance (CL) and volume of distribution (Vd) differed between models. Weight total (WT) was the most frequently reported to be a significant predictor for both parameters, especially for estimating the CL in pediatrics. The PD parameter most widely reported assessing the drug exposure-efficacy relationship was the area under the concentration-time curve to minimum inhibitory concentration (MIC) ratio (AUC0-24/MIC) with different targets proposed for each echinocandin. In certain populations such as patients that are critically ill, obese, receiving extracorporeal membrane oxygenation (ECMO) and/or continuous renal replacement therapy (CRRT), or pediatric patients and/or patients with cancer or that are immunocompromised, the fixed dosing strategies recommended in the drug prescribing information may not reach the PK/PD target. For these populations, different strategies have been proposed, such as a dosing regimen based on body weight or increasing the loading and/or maintenance dose. Despite echinocandins' favorable safety profile and predictable PK, certain groups at risk of suboptimal drug exposure can benefit from therapeutic drug monitoring (TDM) to prevent clinical failures. Numerous popPK models of echinocandins have been developed. However, an external validation of the suggested dosing regimens in conjunction with an analysis of population subgroups should be conducted before implementing a popPK model in clinical practice.

Anidulafungin exposure and population pharmacokinetics in critically ill patients with invasive candidiasis

PURPOSE

Anidulafungin is recommended as a first-line treatment for invasive Candida infections in critically ill patients. Pharmacokinetic (PK) variability is large in critically ill patients, potentially compromising pharmacokinetic-pharmacodynamic (PKPD) target attainment under standard dosing. We aimed to assess anidulafungin exposure, PKPD target attainment, and population (pop)PK in critically ill patients.

METHODS

Adult ICU patients receiving standard anidulafungin dosing [200 mg on day 1, then 100 mg daily] were included (NCT04045366). We performed rich blood sampling on an early (day 2 ± 1) and/or late (day 5 ± 1) treatment day. Using total anidulafungin plasma concentrations, we developed a popPK model (NONMEM7.5) and conducted Monte Carlo simulations (n = 1,000 per virtual patient) to evaluate the impact of patient factors on PKPD target attainment (AUC24h target 83.5 mg×h/L).

RESULTS

Twenty patients contributed 188 anidulafungin concentrations. PKPD target attainment was 45% and 65% on early and late sampling days, respectively. A two-compartment popPK model with first-order elimination described the data. Anidulafungin clearance increased with bodyweight and central volume of distribution increased as serum albumin decreased. Both bodyweight and serum albumin had a clinically relevant impact on PKPD target attainment at day 1 (area under the ROC curve; AUROC 0.82 and 0.62, respectively), and bodyweight on PKPD target attainment at day 14 (AUROC 0.94). Standard anidulafungin dosing regimen fails to achieve adequate target attainment throughout the treatment period.

CONCLUSION

Standard anidulafungin dosing is insufficient for achieving adequate exposure in critically ill patients. An interactive simulation tool is provided to aid dose-finding research and explore different dosing strategies and targets.

Updated antimicrobial dosing recommendations for obese patients

The prevalence of obesity has increased considerably in the last few decades. Pathophysiological changes in obese patients lead to pharmacokinetic (PK) and pharmacodynamic (PD) alterations that can condition the correct exposure to antimicrobials if standard dosages are used. Inadequate dosing in obese patients can lead to toxicity or therapeutic failure. In recent years, additional antimicrobial PK/PD data, extended infusion strategies, and studies in critically ill patients have made it possible to obtain data to provide a better dosage in obese patients. Despite this, it is usually difficult to find information on drug dosing in this population, which is sometimes contradictory. This is a comprehensive review of the dosing of different types of antimicrobials (antibiotics, antifungals, antivirals, and antituberculosis drugs) in obese patients, where the literature on PK and possible dosing strategies in obese adults was critically assessed.

Candidemia in Adult Patients in the ICU: A Reappraisal of Susceptibility Testing and Antifungal Therapy

OBJECTIVE

To provide updates on the epidemiology and recommendations for management of candidemia in patients with critical illness.

DATA SOURCES

A literature search using the PubMed database (inception to March 2023) was conducted using the search terms "invasive candidiasis," "candidemia," "critically ill," "azoles," "echinocandin," "antifungal agents," "rapid diagnostics," "antifungal susceptibility testing," "therapeutic drug monitoring," "antifungal dosing," "persistent candidemia," and "Candida biofilm."

STUDY SELECTION/DATA EXTRACTION

Clinical data were limited to those published in the English language. Ongoing trials were identified through ClinicalTrials.gov.

DATA SYNTHESIS

A total of 109 articles were reviewed including 25 pharmacokinetic/pharmacodynamic studies and 30 studies including patient data, 13 of which were randomized controlled clinical trials. The remaining 54 articles included fungal surveillance data, in vitro studies, review articles, and survey data. The current 2016 Infectious Diseases Society of America (IDSA) Clinical Practice Guideline for the Management of Candidiasis provides recommendations for selecting empiric and definitive antifungal therapies for candidemia, but data are limited regarding optimized dosing strategies in critically ill patients with dynamic pharmacokinetic changes or persistent candidemia complicated.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Outcomes due to candidemia remain poor despite improved diagnostic platforms, antifungal susceptibility testing, and antifungal therapy selection for candidemia in critically ill patients. Earlier detection and identification of the species causing candidemia combined with recognition of patient-specific factors leading to dosing discrepancies are crucial to improving outcomes in critically ill patients with candidemia.

CONCLUSIONS

Treatment of candidemia in critically ill patients must account for the incidence of non-albicans Candida species and trends in antifungal resistance as well as overcome the complex pathophysiologic changes to avoid suboptimal antifungal exposure.

Optimizing anidulafungin exposure across a wide adult body size range

Echinocandins like anidulafungin are first-line therapies for candidemia and invasive candidiasis, but their dosing may be suboptimal in obese patients. Our objective was to quantify anidulafungin exposure in a cohort of adults across a wide body size range to test if body size affects anidulafungin pharmacokinetics (PK). We enrolled 20 adults between the ages of 18 and 80 years, with an equal distribution of patients above and below a body mass index of 30 kg/m2. A single 100-mg dose of anidulafungin was administered, followed by intensive sampling over 72 h. Population PK analysis was used to identify and compare covariates of anidulafungin PK parameters. Monte Carlo simulations were performed to compute the probability of target attainment (PTA) based on alternative dosing regimens. Participants (45% males) had a median (range) age of 45 (21-78) years and a median (range) weight of 82.7 (42.4-208.3) kg. The observed median (range) of AUC0-∞ was 106.4 (51.9, 138.4) mg∙h/L. Lean body weight (LBW) and adjusted body weight (AdjBW) were more influential than weight as covariates of anidulafungin PK parameters. The conventional 100 mg daily maintenance is predicted to have a PTA below 90% in adults with an LBW > 55 kg or an AdjBW > 75 kg. A daily maintenance dose of 150-200 mg is predicted in these heavier adults. Anidulafungin AUC0-∞ declines with increasing body size. A higher maintenance dose will increase the PTA compared to the current approach in obese patients.

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.

Echinocandin exposures in obese patients: A scoping review and clinical perspectives

PURPOSE

Echinocandins are favored drugs for the treatment of fungal infections. There is growing evidence that obese patients treated with echinocandins have lower exposures due to pharmacokinetic (PK) alterations. We conducted a scoping review to characterize, evaluate, and summarize the available evidence on echinocandins exposures in obese patients.

SUMMARY

A comprehensive search of PubMed, Embase, and Cochrane Library for studies on echinocandins published from database inception to October 28, 2022, was conducted using PRISMA-ScR methodology. A total of 25 studies comprising more than 3,174 subjects (8 micafungin studies, 7 caspofungin studies, 9 anidulafungin studies, and 1 rezafungin study) were included in this review. Seventeen studies reported lower echinocandins exposures in overweight and obese individuals compared with normal-weight individuals; the authors of these studies recommended dose adjustments. Conversely, 8 studies did not find significant differences in echinocandin exposure among subjects in varying body weight categories. Clinicians may consider dose adjustments of echinocandins in obese patients; however, there is limited evidence on the ideal dose adjustment strategy to overcome the low echinocandins exposures in obese patients.

CONCLUSION

This scoping review shed light on a growing body of evidence indicating that obese patients have lower echinocandin exposures relative to targeted PK indices, which may lead to negative therapeutic implications. Currently, a lack of high-quality evidence impedes reaching consensus on recommendations for echinocandin dosing adjustment in obese patients. Future research evaluating the optimal echinocandin dosing strategy for obese patients is needed.

Therapeutic Drug Monitoring of Antifungal Agents in Critically Ill Patients: Is There a Need for Dose Optimisation?

Invasive fungal infections are an important cause of morbidity and mortality, especially in critically ill patients. Increasing resistance rates and inadequate antifungal exposure have been documented in these patients, due to clinically relevant pharmacokinetic (PK) and pharmacodynamic (PD) alterations, leading to treatment failure. Physiological changes such as third spacing (movement of fluid from the intravascular compartment to the interstitial space), hypoalbuminemia, renal failure and hepatic failure, as well as common interventions in the intensive care unit, such as renal replacement therapy and extracorporeal membrane oxygenation, can lead to these PK and PD alterations. Consequently, a therapeutic target concentration that may be useful for one patient may not be appropriate for another. Regular doses do not take into account the important PK variations in the critically ill, and the need to select an effective dose while minimising toxicity advocates for the use of therapeutic drug monitoring (TDM). This review aims to describe the current evidence regarding optimal PK/PD indices associated with the clinical efficacy of the most commonly used antifungal agents in critically ill patients (azoles, echinocandins, lipid complexes of amphotericin B, and flucytosine), provide a comprehensive understanding of the factors affecting the PK of each agent, document the PK parameters of critically ill patients compared to healthy volunteers, and, finally, make recommendations for therapeutic drug monitoring (TDM) of antifungals in critically ill patients.

Recent advances in fungal serine protease inhibitors

Four types of antifungal drugs are available that include inhibitors of ergosterol synthesis, of fungal RNA biosynthesis, and of cell wall biosynthesis as well as physiochemical regulators of fungal membrane sterols. Increasing resistance to antifungal drugs can severely limit treatment options of fungal nail infections, vaginal candidiasis, ringworm, blastomycosis, histoplasmosis, and Candida infections of the mouth, throat, and esophagus, among other infections. Development of strategies focused on new fungicides can effectively help tackle troublesome fungal diseases. The virulence and optimal growth of fungi depend on various extracellular secreted factors, among which proteases, such as serine proteases, are of particular interest. A specific extracellular proteolytic system enables fungi to survive and penetrate the tissues. Given the role of fungal proteases in infection, any molecule capable of selectively and specifically inhibiting their activity can lead to the development of potential drugs. Owing to their specific mode of action, fungal protease inhibitors can avoid fungal resistance observed with currently available treatments. Although fungal secreted proteases have been extensively studied as potential virulence factors, our understanding of the substrate specificity of such proteases remains poor. In this review, we summarize the recent advances in the design and development of specific serine protease inhibitors and provide a brief history of the compounds that inhibit fungal serine protease activity.

Breakthrough invasive fungal infections in liver transplant recipients exposed to prophylaxis with echinocandins vs other antifungal agents: A systematic review and meta-analysis

INTRODUCTION

Although echinocandins are recommended as first-line prophylaxis for high-risk orthotopic liver transplant (OLT) recipients, occurrence of breakthrough-invasive fungal infections (IFIs) remains a serious concern. We aim to assess the risk of breakthrough IFIs among OLT recipients exposed to prophylaxis with echinocandins compared to other antifungals.

MATERIALS AND METHODS

Two authors independently searched PubMed-MEDLINE, Embase, study registries and reference lists from inception to March 2021, to retrieve randomised controlled trials (RCTs) or observational studies comparing efficacy and safety of echinocandins vs other antifungals for prophylaxis in OLT recipients. Data were independently extracted from two authors, and the quality of included studies was independently assessed according to ROB 2.0 tool for RCTs and ROBINS-I tool for observational studies. The primary outcome was occurrence of breakthrough IFI at the end of prophylaxis (EOP).

RESULTS

698 articles were screened, and ten studies (3 RCTs and 7 observational) were included. No difference between echinocandins and other antifungals in terms of breakthrough IFIs at the EOP emerged both from RCTs (odds ratio [OR] 0.85, 95% CI 0.24-2.99) and observational studies (OR 1.43, 95% CI 0.28-7.40). No difference emerged also for secondary outcomes. In the subgroup comparison between echinocandins and polyenes, a trend for higher risk of breakthrough IFI at the EOP (OR 4.82, 95% CI 0.97-24.03) was noted.

CONCLUSIONS

Echinocandins do not seem to be associated with increased risk of breakthrough IFIs in OLT recipients. However, the large diversity in the comparator group hinders a definitive interpretation. Further studies exploring the relationship between echinocandin use and breakthrough IFIs according to specific comparators are warranted.

Pharmacokinetics of echinocandins in suspected candida peritonitis: A potential risk for resistance

INTRODUCTION

A possible increase in Candida resistance, especially in Candida glabrata, has been speculated according to poor diffusion of echinocandins to peritoneal fluid.

MATERIALS/METHODS

Peritoneal and serum concentrations of caspofungin, micafungin and anidulafungin were analysed in surgical patients with suspected candida peritonitis. After 4 days of starting therapy, serum and peritoneal samples (through peritoneal drainage) were obtained at baseline, 1, 6, 12 and 24 h of drug administration. Micafungin and anidulafungin concentrations were determined using high-performance liquid chromatography (HPLC/F), whereas caspofungin concentrations were established by bioassay.

RESULTS

Twenty-three critically ill patients with suspected abdominal fungal infection who were receiving an echinocandin were prospectively recruited. No specific criteria were applied to prescribe one specific echinocandin. No special clinical differences were observed among the three groups of patients. All were receiving antibiotic therapy, 80% required inotropic drugs, and fungal peritonitis was confirmed in 74% of them. The AUC_{0_24h} (mg × h/L) obtained in serum and peritoneal fluid were: 126.84 and 34.38, 98.52 and 18.83, and 66.9 and 8.78 for anidulafungin, micafungin and caspofungin, respectively. The median concentration in peritoneal fluid ranged from 0.66 to 1.82 μg/mL for anidulafungin, 0.68-0.88 μg/mL for micafungin and 0.21-0.46 μg/mL for caspofungin.

CONCLUSION

The results showed moderate penetration of echinocandins into the peritoneal fluid of these patients. These levels are below the threshold of resistance mutant selection published by other authors. This could justify a potential risk of resistance in patients with prolonged treatment with echinocandins and suboptimal control of abdominal infection.

Population pharmacokinetics of anidulafungin in ICU patients assessing inter- and intrasubject variability

AIMS

The population pharmacokinetics (PK) of anidulafungin in critically ill patients hospitalized in intensive care units (ICUs) was explored with the intention of evaluating and optimizing dosing regimens.

METHODS

A PK study was conducted in a cohort of 13 patients treated with anidulafungin using intensive sampling during multiple periods per patient and the high-performance liquid chromatography method for drug quantification. A population PK model was developed to describe the concentration-time course of anidulafungin and the inter-individual (IIV) and interoccasion variability (IOV) of the PK parameters. Model-based PK simulations have been performed to estimate the probability of target attainment (PTA), given the pharmacokinetic/pharmacodynamic target of free 24-hour area under the free drug concentration-time curve over minimum inhibitory concentration for several dosing regimens.

RESULTS

A two-compartment PK model, with first-order elimination, best described the data with population clearance (CL) and central/peripheral volume of distribution (V1/V2) of 0.778 L/h and 10.2/21.1 L, respectively, and a mean ± s.d. AUC_0-24 of 119.97 ± 46.23 mg·h/L. Pronounced IIV and IOV variability was found for CL (38% and 31%) and V1 (47% and 30%), respectively. Sequential Organ Failure Assessment (SOFA) and Body Mass Index (BMI) were found to be covariates on CL and V1, respectively. Low PTA values were calculated for borderline Clinical & Laboratory Standards Institute (CLSI)-susceptible Candida strains.

CONCLUSIONS

Although anidulafungin exposure was found comparable to that in healthy volunteers, elevated interindividual and significant interoccasion variability was found in critically ill ICU patients, which resulted in reduced PTA values in these patients.

Comparative pharmacokinetics of the three echinocandins in ICU patients

Background

We conducted a prospective study in ICU patients of two tertiary hospitals in order to determine basic pharmacokinetic (PK) parameters, associated variation and target attainment rates for anidulafungin, micafungin and caspofungin.

Methods

Serum samples from patients treated for 7 days with the standard doses of anidulafungin (N = 13), micafungin (N = 14) or caspofungin (N = 7) were analysed by validated chromatographic methods. PK parameters determined with non-compartmental analysis were correlated with demographic, laboratory and disease severity characteristics. The percentages of patients attaining drug exposures described in the summary of product characteristics (SmPC) documents and preclinical PK/PD targets for stasis were estimated.

Results

The median (range) AUC24 was 101.46 (54.95–274.15) mg·h/L for anidulafungin, 79.35 (28.00–149.30) mg·h/L for micafungin and 48.46 (19.44–103.69) mg·h/L for caspofungin. The interindividual variability of anidulafungin, micafungin and caspofungin AUC24 was 46%–58%, attributed mainly to variability in volume of distribution (V), clearance (CL) and in both V and CL, respectively. Significant correlations were found between anidulafungin AUC24 and BMI (rs = −0.670, P = 0.012) and liver enzymes (rs = 0.572–0.665, P = 0.013–0.041) and between caspofungin Cmin and transaminase levels (rs = −0.775 to −0.786, P = 0.036–0.041). Less than 50% of our patients attained the corresponding SmPC median AUC24s and none of the patients attained the PK/PD targets for Candida albicans and Candida parapsilosis.

Conclusions

Anidulafungin exposure in ICU patients was comparable with that reported in non-ICU patients and in healthy volunteers. Micafungin exposure was comparable to that of other patients but ∼30% lower than that in healthy volunteers, whereas caspofungin exposure was rather low (∼50% lower than in healthy volunteers). Larger interindividual variability (50%–60%) was recorded in ICU patients compared with other groups for all three echinocandins.