Comparative Pharmacodynamics of Echinocandins against Aspergillus fumigatus Using an In Vitro Pharmacokinetic/Pharmacodynamic Model That Correlates with Clinical Response to Caspofungin Therapy: Is There a Place for Dose Optimization?

Echinocandins have been used as primary therapy of invasive aspergillosis (IA), with suboptimal results at standard dosing. Here, we explored the efficacy of dose escalation in a validated in vitro pharmacokinetic/pharmacodynamic (PK/PD) model. Six echinocandin wild-type (WT) and three non-WT A. fumigatus isolates were tested in an in vitro PK/PD model simulating anidulafungin, caspofungin, and micafungin exposures with a free drug maximum concentration (fCmax) of 0.01 to 16 mg/liter and a half-life (t1/2) of 8 to 22 h. The relationship between the area under the dosing interval time-free drug concentration curve (fAUC0-24)/minimum effective concentration (MEC) and % aberrant mycelium formation was analyzed. PK/PD indices associated with 50 to 99.99% maximal activity (EI50 to EI99.99) were correlated with the clinical outcome of a 50-mg/day standard dose of caspofungin. The probability of target attainment (PTA) was calculated for different dosing regimens of each echinocandin via Monte Carlo analysis. A sigmoidal PK/PD relationship was found for WT isolates with EI99 values of 766, 8.8, and 115 fAUC0-24/CLSI MEC for anidulafungin, caspofungin, and micafungin, respectively. No aberrant mycelia were observed for non-WT isolates, irrespective of their MEC and drug exposure. The EI99, EI99.9, and EI99.99 values corresponded to 2-, 3-, and 4-log10 formation of aberrant mycelia and correlated with survival, favorable, and complete response rates to caspofungin primary therapy in patients with IA. A very low PTA (<13%) was found for the standard doses of all echinocandins, whereas a PTA of ≥90% was found with 100 and 150 mg/day of caspofungin and 1,400 mg/day micafungin against WT isolates. For anidulafungin, the PTA for 1,500 mg/day was 10%. Among the three echinocandins, only caspofungin at 2 or 3 times the licensed dosing was associated with a high PTA. Caspofungin dose escalation might deserve clinical validation.

Pharmacokinetic/pharmacodynamics variability of echinocandins in critically ill patients: A systematic review and meta-analysis

WHAT IS KNOWN AND OBJECTIVE

Anidulafungin, caspofungin and micafungin are three widely used echinocandin drugs licensed for the treatment of invasive fungal infections, and their clinical use is widespread. To evaluate pharmacokinetic/pharmacodynamics variability of echinocandins in critically ill patients by comparing the differences in pharmacokinetic parameters between critically ill patients and healthy volunteers or general patients.

METHODS

MEDLINE, EMBASE, The Cochrane Library and Pubmed were searched from inception until 6 September 2018. Studies investigating the pharmacokinetic parameters of echinocandins in critically ill patients, healthy volunteers or general patients were included. Our primary outcomes included AUC0-24 h , Cmax and Cmin (24 hours). Two reviewers independently reviewed all titles, abstracts and text, and extracted data. We applied R software (R 2017) to conduct meta-analysis.

RESULTS AND DISCUSSION

Of 3235 articles screened, 17 studies were included in the data synthesis. Descriptive data from single-arm studies show that critically ill patients who received caspofungin had more stable AUC0-24 h than those who received anidulafungin and micafungin. The Cmax of critically ill patients who received caspofungin and micafungin was similar to healthy volunteers. However, the Cmax in critically ill patients who received anidulafungin was lower than in healthy volunteers. The Cmin and T1/2 of critically ill patients who received caspofungin were larger than in healthy volunteers. The Vd and CL of critically ill patients receiving anidulafungin and micafungin were larger than in healthy volunteers.

WHAT IS NEW AND CONCLUSION

This systematic review provides an analysis of the pharmacokinetic/pharmacodynamics variability of echinocandins in critically ill patients. Based on the limited data available, caspofungin has less pharmacokinetic/pharmacodynamics variability than anidulafungin and micafungin.

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.

Clinical Pharmacokinetics and Pharmacodynamics of Micafungin

Micafungin is a selective inhibitor of the synthesis of fungal 1,3-β-d-glucan, an essential component of the fungal cell wall. It is available as a powder for infusion only and is registered for the treatment of invasive and esophageal candidiasis in addition to prophylaxis of Candida infections in both adults and children. Average exposure after a single intravenous 100 mg dose in healthy adults is 133 mg h/L. Both exposure and maximum plasma concentration show linear dose proportional pharmacokinetics (PK) over a 0.15–8 mg/kg dose range. In healthy adults, the clearance (CL) is 10.4 mL/h/kg and volume of distribution is 0.2 L/kg; both are independent of the dose. Micafungin is metabolized by arylsulfatase, catechol-O-methyltransferase, and several cytochrome P450 (CYP) isoenzymes (3A4, 1A2, 2B6 and 2C), but no dose adjustments are necessary in patients with (severe) hepatic dysfunction. Exposure to micafungin is lower in hematology patients, and is even further lowered in critically ill patients (including burn patients) compared with healthy volunteers, which might have consequences for treatment efficacy. In children, an increased CL has been reported: 40–80 mL/h/kg in premature neonates and 20 mL/h/kg in children >4 months of age. Therefore, relatively higher doses of 4–10 mg/kg in premature neonates and 2–4 mg/kg in children with invasive candidiasis are used. However, these higher CLs may also be explained by the eightfold higher free fraction of unbound micafungin in premature neonates, meaning that an augmented dose might not be required.

Population Pharmacokinetic Model and Pharmacokinetic Target Attainment of Micafungin in Intensive Care Unit Patients

OBJECTIVE

To study the pharmacokinetics of micafungin in intensive care patients and assess pharmacokinetic (PK) target attainment for various dosing strategies.

METHODS

Micafungin PK data from 20 intensive care unit patients were available. A population-PK model was developed. Various dosing regimens were simulated: licensed regimens (I) 100 mg daily; (II) 100 mg daily with 200 mg from day 5; and adapted regimens 200 mg on day 1 followed by (III) 100 mg daily; (IV) 150 mg daily; and (V) 200 mg daily. Target attainment based on a clinical PK target for Candida as well as non-Candida parapsilosis infections was assessed for relevant minimum inhibitory concentrations [MICs] (Clinical and Laboratory Standards Institute). Parameter uncertainty was taken into account in simulations.

RESULTS

A two-compartment model best fitted the data. Clearance was 1.10 (root square error 8%) L/h and V 1 and V 2 were 17.6 (root square error 14%) and 3.63 (root square error 8%) L, respectively. Median area under the concentration-time curve over 24 h (interquartile range) on day 14 for regimens I-V were 91 (67-122), 183 (135-244), 91 (67-122), 137 (101-183) and 183 (135-244) mg h/L, respectively, for a typical patient of 70 kg. For the MIC/area under the concentration-time curve >3000 target (all Candida spp.), PK target attainment was >91% on day 14 (MIC 0.016 mg/L epidemiological cut-off) for all of the dosing regimens but decreased to (I) 44%, (II) 91%, (III) 44%, (IV) 78% and (V) 91% for MIC 0.032 mg/L. For the MIC/area under the concentration-time curve >5000 target (non-C. parapsilosis spp.), PK target attainment varied between 62 and 96% on day 14 for MIC 0.016.

CONCLUSIONS

The licensed micafungin maintenance dose results in adequate exposure based on our simulations with a clinical PK target for Candida infections but only 62% of patients reach the target for non-C. parapsilosis. In the case of pathogens with an attenuated micafungin MIC, patients may benefit from dose escalation to 200 mg daily. This encourages future study.

Altered Micafungin Pharmacokinetics in Intensive Care Unit Patients

Micafungin is considered an important agent for the treatment of invasive fungal infections in the intensive care unit (ICU). Little is known on the pharmacokinetics of micafungin. We investigated micafungin pharmacokinetics (PK) in ICU patients and set out to explore the parameters that influence micafungin plasma concentrations. ICU patients receiving 100 mg of intravenous micafungin once daily for suspected or proven fungal infection or as prophylaxis were eligible. Daily trough concentrations and PK curves (days 3 and 7) were collected. Pharmacokinetic analysis was performed using a standard two-stage approach. Twenty patients from the ICUs of four hospitals were evaluated. On day 3 (n = 20), the median (interquartile range [IQR]) area under the concentration-time curve from 0 to 24 h (AUC0-24) was 78.6 (65.3 to 94.1) mg · h/liter, the maximum concentration of drug in serum (Cmax) was 7.2 (5.4 to 9.2) mg/liter, the concentration 24 h after dosing (C24) was 1.55 (1.4 to 3.1) mg/liter, the volume of distribution (V) was 25.6 (21.3 to 29.1) liters, the clearance (CL) was 1.3 (1.1 to 1.5) liters/h, and the elimination half-life (t1/2) was 13.7 (12.2 to 15.5) h. The pharmacokinetic parameters on day 7 (n = 12) were not significantly different from those on day 3. Daily trough concentrations (day 3 to the end of therapy) showed moderate interindividual (57.9%) and limited intraindividual variability (12.9%). No covariates of the influence on micafungin exposure were identified. Micafungin was considered safe and well tolerated. We performed the first PK study with very intensive sampling on multiple occasions in ICU patients, which aided in resolving micafungin PK. Strikingly, micafungin exposure in our cohort of ICU patients was lower than that in healthy volunteers but not significantly different from that of other reference populations. The clinical consequence of these findings must be investigated in a pharmacokinetic-pharmacodynamic (PK-PD) study incorporating outcome in a larger cohort. (This study is registered at ClinicalTrials.gov under registration no. NCT01783379.).

Impact of special patient populations on the pharmacokinetics of echinocandins

Echinocandins belong to the class of antifungal agents. Currently, three echinocandin drugs are licensed for intravenous treatment of invasive fungal infections: anidulafungin, caspofungin and micafungin. While their antifungal activity overlaps, there are substantial differences in pharmacokinetics (PK). Numerous factors may account for variability in PK of echinocandins including age (pediatrics vs adults), body surface area and body composition (normal weight vs obesity), disease status (e.g., critically ill and burn patients) and organ dysfunction (kidney and liver impairment). Subsequent effects of altered exposure might impact efficacy and safety. Knowledge of PK behavior is crucial in optimal clinical utilization of echinocandin in a specific patient or patient population. This review provides up-to-date information on PK data of anidulafungin, caspofungin and micafungin in special patient populations. Patient populations addressed are neonates, children and adolescents, obese patients, patients with hepatic or renal impairment, critically ill patients (including burn patients) and patients with hematological diseases.

Pharmacokinetics of micafungin in subjects with severe hepatic dysfunction

Micafungin is an echinocandin with potent activity against a broad range of fungal species, including Candida species. The pharmacokinetic and safety profiles of micafungin have been evaluated in individuals with mild-to-moderate hepatic dysfunction, but not in individuals with severe hepatic dysfunction. Therefore, the present study assessed the pharmacokinetics and safety of a single 100 mg dose of micafungin in healthy subjects (n = 8) and subjects with severe hepatic dysfunction (n = 8). Mean maximum plasma concentration of micafungin and mean area under the plasma micafungin concentration-time curve extrapolated to infinity were lower in subjects with severe hepatic dysfunction (7.3 ± 2.4 µg/mL and 100.1 ± 34.5 h·μg/mL, respectively) than in subjects with normal hepatic function (10.3 ± 2.5 µg/mL and 142.4 ± 28.9 h·μg/mL, respectively). Mean clearance was higher in subjects with severe hepatic dysfunction (1,098 ± 347 mL/h) than in subjects with normal hepatic function (728 ± 149 mL/h). Concentrations of albumin in subjects with severe hepatic dysfunction were lower. Assessments of micafungin plasma protein binding suggested that the higher clearance in subjects with severe hepatic dysfunction may be due to higher unbound concentrations. However, the magnitude of the differences was not considered clinically meaningful and is comparable with exposures reported elsewhere for a 100-mg dose in patients treated for invasive candidiasis. Thus, dose adjustment in subjects with severe hepatic dysfunction is not warranted. Micafungin was well tolerated in all subjects throughout the study.