Analysis of Parameters and Dosage Regimen of Posaconazole against Candida spp. and Aspergillus spp. Using Monte Carlo Simulation

Invasive fungal infections (IFI) have recently become increasingly more pre-valent, resulting in an increased risk of morbidity and mortality. Both Candida spp. and Aspergillus spp. are major causes of IFI. In this study, we aimed to evaluate the cumulative fraction of response of various dosage regimens of posaconazole against nine Candida spp. and six Aspergillus spp. in both children and adults. Monte Carlo simulation (MCS) was performed to op-timize selection of posaconazole dosage regimens. For children, a dosage regimen of 120 mg/m 2 posaconazole tid was sufficient to treat fungal infections caused by all six Aspergillus spp. and six of the nine Candida spp. (but was not effective against C. glabrata, C. guilliermondii and C. krusei). In contrast, a 400 mg dosage regimen of posaconazole bid achieved the target pharmaco-kinetic/pharmacodynamics (PK/PD) parameters against all six Aspergillus spp. and eight of the nine Candida spp. (but was not effective against C. glabrata) in the adults. Dosage regimens of 50 mg bid, 100 mg bid, or 200 mg bid were not effective. Posaconazole dosage regimens are likely to achieve their desired PK/PD targets against Candida spp. and Aspergillus spp. in both children and adults.


Introduction
Invasive fungal infections (IFI) have recently become increasingly more preva-How to cite this paper: Wang, Y., Zhao, J.Y., Hu, J.H., Zhao, X.H. and Yao, Y.H. (2020) Analysis of Pharmacokinetic/Pharmacodynamic Parameters and Dosage Re-with potent in vitro and in vivo activities against a large number of clinically important yeasts and models [4] [5]. Posaconazole dissolves readily in lipids, is orally absorbed, and distributes significantly throughout the tissues. However, the dosage regimen can significantly influence the relative bioavailability of posaconazole, which can also be significantly increased by the administration of high-fat containing food [6] [7] [8]. The pharmacokinetics of posaconazole administered by oral suspension is characterized by low bioavailability, unpredictable plasma concentrations, and large inter-individual patient variability [9]. Assessing various dosage regimens is necessary to better understand differences in clinical response.
To maximize the likelihood of favorable clinical outcomes and minimize the probability of antimicrobial resistance, Monte Carlo simulation (MCS) is a very useful tool for determining the appropriate dose in most therapeutic areas [10] [11] [12] [13] [14]. MCS can be implemented to evaluate antifungal agent dosage regimens to integrate variables including pharmacokinetic (PK) parameters, minimum inhibitory concentration (MIC) distribution, and pharmacodynamic (PD) information. MCS is not only applied to many kinds of antimicrobial agents, but also applied to MIC breakpoints [15] [16] [17]. For example, Mouton JW et al. reveal the provisional breakpoint of BAL9141 is S (susceptible) < 4 mg/liter using MCS [16]. Doan TN et al. investigate the probability of target attainment (PTA) of various anidulafungin dosing regimens against Candida spp.
in patients with acute leukaemia using MCS [15]. Therefore, we aimed to optimize selection of posaconazole dosage regimens by evaluating the probability of attaining target PD exposure against a wide range of clinical isolates of Candida spp. and Aspergillus spp. using MCS.

Pharmacokinetics
Information regarding the pharmacokinetic parameters of posaconazole was  [19]. Phase 1 studies were randomized and double-blind, and consisted of a placebo-controlled group and a parallel-group.
Male and female volunteers ranging in age from 19 to 43 were randomly assigned to either receive treatment with posaconazole oral tablets (50 to 400 mg) or placebo tablets to be taken twice daily for 14 days [18]. Pharmacokinetic data of children aged 13 years or younger suffering from a hematologic malignancy were treated prophylactically with posaconazole oral suspension at a dose of 120 mg/m 2 three times daily, as reported by Vanstraelen K [19]. Information from studies that evaluated clinically relevant dosage regimens and provided the mean results for the pharmacokinetic parameters of interest with corresponding measures of variability of areas under the concentration-time curve at steady-state (AUCs) were included ( Table 1).

Monte Carlo Simulation
A pharmacodynamic study of posaconazole in a murine model of disseminated Candidiasis demonstrated that the free-drug ratio of AUC/MIC at 24 h ≥ 16.9 was the critical predictor of response to posaconazole therapy [20]. Furthermore, the free-drug posaconazole AUC/MIC ratio PD target at 24 hours was 1.09 for the wild-type and mutant isolates of Aspergillus in an in vivo model of invasive pulmonary Aspergillosis [21]. The free-drug AUC/MIC ratios of posaconazole at 24 hours for other pharmacodynamic targets of Candidiasis (6 -30) and  were also displayed for each MCS.
The pharmacokinetic parameters were determined to as the lognormal distribution obtained with a mean and a percentage coefficient of variance (CV%). In the case of MIC, the data obtained from Candida spp. and Aspergillus spp. were assumed to follow a discrete distribution. Posaconazole protein binding was set at a constant value of 98% [6]. CrystalBall software (Fusion Edition, version 11.1.2.4.600, Oracle) was used for the Monte Carlo simulation consisting of 1000 subjects. The percentage of subjects who achieved the requisite pharmacodynamic exposure (fAUC 0-24 /MIC) for each antibiotic dosage regimen/bacterial population combination is termed the probability of target attainment (PTA) [22]. The cumulative fraction of response (CFR) refers to the expected population PTA for a specific drug dose and a specific population of microorganisms [22].
The corresponding PTA of Candida spp. was determined at a fixed MIC value in the range of 0.008 -32 μg/ml. For the calculation of PTA (Aspergillus spp.), MIC values were fixed from 0.01 to 32 μg/ml. Calculation of CFR was achieved using data based on the corresponding MIC distribution, whereby CFR values > 90% were considered optimal for a dosage regimen against a population of organisms.   Figure 1(a)). The chosen targets for Aspergillus spp. were fAUC 0-24 /MIC ≥ 1.09.

CFR Analysis
To increase the clinical relevance of this study, several PK/PD targets for Candida spp. (from 6 to 30) and Aspergillus spp. (from 0.4 to 2) were analyzed by Monte Carlo simulation to simulate species-specific CFR expectation values ( Figure 2 and Figure 3). Increased PK/PD target values led to reduced CFR expectation values.

Discussion
In this study, we used MCS analysis to investigate the ability of posaconazole dosage regimens to achieve their requisite PK/PD target against nine Candida spp. and six Aspergillus spp. in both children and adults. Previous studies have demonstrated the efficacy of posaconazole against a variety of Candida spp. and Aspergillus spp.   A. niger and A. nidulans). However, none of the simulated dosage regimens were effective against C. guilliermondii or C. krusei in children. Similarly, use of posaconazole doses of 50 mg bid or 100 mg bid was also ineffective against C. guilliermondii and C. krusei in adults. Increased doses (e.g. 200 mg bid) against C. krusei in adults resulted in CFR values ranging from 83.15% to 94.80%, demonstrating improved efficacy. This effect was not observed in C. guilliermondii. In addition, none of the posaconazole dosage regimens investigated achieved CFRs > 90% against C. glabrata. These results were consistent with MIC distributions that resulted in a CFR of 88.77% in C. glabrata (MIC range, 0.125 to 32 μg/ml).
Posaconazole is currently available as an oral formulation due to its poor aqueous solubility. Posaconazole oral suspension absorption is unpredictable and is often affected by concomitant medications and mucositis [27]. nazole than adults. The need for a relatively higher dose in pediatric patients is due to a higher clearance rate of the drug per kilogram of body weight compared to adults [27]. Currently, the recommended dosage regimen of posaconazole is 400 mg twice daily with food for refractory oropharyngeal candidiasis or refractory invasive aspergillosis. In patients who cannot tolerate solid food, 200 mg posaconazole should be administered four times daily with a nutritional supplement [27]. These clinical dosage regimens are consistent with the results that found CFR > 90% (400 mg bid) against eight Candida spp. and six Aspergillus spp. in adults, and suggest that clinical use of this regimen is appropriate [28].
Dose adjustments are not necessary for patients with renal or hepatic dysfunction. This is the first study to analyze the differences in CFR of posaconazole against Candida spp. and Aspergillus spp. in children and adults. However, there are some potential limitations to this study. First, the PK parameters of posaconazole were collected from a relatively small sample size of children and adults.
In addition, an important weakness of the use of posaconazole oral solution is that there is not any data available regarding the PK parameters of intravenous or delayed-release oral formulations. Furthermore, this MCS analysis only considered serum pharmacokinetics, which could be useful for evaluation of bloodstream infections but not for other sites of infection such as tissue. Finally, antimicrobial use and local susceptibility should be considered when PK/PD modeling is applied to the predicted clinical outcome.

Conclusion
In conclusion, the results of PK/PD modeling and Monte Carlo simulations suggest that the currently approved high-dose regimen of posaconazole (400 mg bid) is sufficient to treat adults for fungal infections by Aspergillus spp. and Candida spp., with the exception of C. glabrata. In addition, we were able to determine that the dosage regimen of posaconazole (120 mg/m 2 tid) in children was most likely to attain the requisite PK/PD targets against Aspergillus spp. This was effective against Candida infections in children except C. glabrata, C. guilliermondii, and C. krusei. As such, further studies should focus on optimization of posaconazole dosage regimens to improve the probability of treatment success for specific fungal infections. Simulation by PK/PD modelling is a crucial tool with the potential to guide antibiotic therapy.

Funding
This work was funded by the Chengde Science and Technology Planning Project (No. 201701A086).

Data Availability Statement
All data generated or analyzed during this study are included in this published article.

Conflicts of Interest
The authors declare no conflict of interest.