Hematological disorders patients are susceptible to fungal infections. Posaconazole (PCZ) is a new-generation triazole with broad-spectrum antifungal activity against a variety of fungal pathogens. Because it is generally well tolerated and the majority of its adverse side effects are similar to those of other triazoles (Huang et al., 2012; Shen et al., 2013), PCZ is potentially an important agent in the treatment and prevention of invasive fungal infections (IFIs) in hematological disorders patients (Cornely et al., 2007; Ullmann et al., 2007).

PCZ shows significantly variable bioavailability due to erratic absorption, especially with the oral suspension formulation, which is influenced by food, some medications and gastric absorption disorders. Up to 4-fold increase in the exposure of the oral PCZ suspension was reported when administered with food (Krishna et al., 2009). Conversely, medications that increase gastric pH, such as proton pump inhibitors (PPIs) and histamine H₂-blockers, have been shown to decrease PCZ exposure to a considerable extent (Dolton et al., 2012). However, conclusive clinical studies investigating the effects of gender and inflammation on PCZ metabolism are lacking, although a few differences have been reported in terms of clinical outcome and physiological and pharmacological effects between men and women undergoing PCZ (Allegra et al., 2017; Jeong et al., 2018). Besides, clinically significant effect of C-reactive protein (CRP) on PCZ concentration was not observed in a prospective study by Märtson et al. (2019a).

Moreover, a significant correlation between clinical response and PCZ concentrations has been demonstrated, and findings from these studies have shown that monitoring PCZ concentration is necessary to improve antifungal effect (Dolton et al., 2012; Moore et al., 2015). However, real-world data in this field is limited, especially in Asian populations. One Chinese study suggested that the concentration of PCZ affects the probability of response to prophylaxis of fungal infections, but factors, other than PPIs, affecting PCZ concentrations were not investigated so far (Li et al., 2020). One South Korea study suggested that hypoalbuminemia influences PCZ concentrations, but the concentration-to- response relationship was not explored (Oh et al., 2020). The aim of present study was to examine the impact of PCZ concentration on the clinical response and hepatotoxicity in Chinese patients with hematological disorders, and to investigate potential factors that may affect PCZ concentration.

PCZ was initially approved as an oral suspension formulation in 2006, then delayed-release solid tablets and an intravenous formulation were approved in 2013 and 2014, respectively. Although these formulations have proved to be more effective in fungal prophylaxis without increasing side effects. PCZ oral suspension is still an important alternative to patients with swallowing difficulties in circumstances where the intravenous formulation is not available. However, the bioavailability of PCZ oral suspension is affected by various conditions, including erratic absorption, which is influenced by food, the concomitant use of medications, gut motilityand gastric absorption disorders. The present study provided real-world PCZ oral suspension concentration data and showed that significant variability in PCZ oral suspension C_min exists among different patients (Figure 3). The concentration may be affected by diarrhoea, body weight, male gender, and co-administration of PPIs (Miceli et al., 2015; Cojutti et al., 2018). All these factors make it difficult to attain optimal target concentrations. But factors that could potentially contribute to such variability remain to be fully elucidated. Additionally, Jeong et al. reported that escalating the PCZ suspension dose beyond 800 mg daily did not appear to result in consistent increases in C_min (Jeong et al., 2018). From this viewpoint, it seemed not be appropriate to predict the blood drug concentration completely based on the drug dose in order to achieve the therapeutic window.

In this study, 46 patients treated with PCZ suspension for prophylaxis of IFI were monitored. Logistic regression analysis revealed that the PCZ C_min value of 0.76 µg/mL was associated with >80% probability of successful therapy (Wang et al., 2014). Similar to a prospective study of PCZ prophylaxis of IFIs in patients with hematological diseases [the success rate was (64/74) 86.5%] (Li et al., 2020), and a randomized clinical trial for prophylaxis against IFIs [the success rate was (85/91) 93.5%] (Jang et al., 2010), the current study found that 83.3% of patients (30/36) successfully responded to PCZ prophylaxis. In agreement with the previous study (Chau et al., 2014), a PCZ C_min of 1.0 µg/mL was chosen as the lower limit to treatment of a proven, probable, or possible IFI, and the logistic regression model showed that this C_min was associated with a probability of successful response of 80.5% (Figure 3B). Our lower limit, however, is different from that previously published by Walsh et al. (2007). In that report, for patients with average plasma concentrations >1.25 µg/mL, clinical effectiveness was increased to 75%. In this analysis, a cut-off C_min was identified for patients as the concentration where successful clinical response increased >80% probability (Wang et al., 2014).

Similar to findings of Dolton et al. (2012) and Jeong et al. (2018), the present study found no relationship between PCZ C_min and hepatotoxicity, although the PCZ plasma concentrations were numerically higher among patients who undergone PCZ-related hepatotoxicity. The treatment for one patient who received PCZ suspension for prophylaxis fungal infection was seitched to carpofungin when alanine transaminase levels and aspartate transaminase levels increased more than five times the upper limit of normal. The PCZ concentrations in this patient ranged between 0.65–1.02 µg/mL. Cessation of PCZ led to gradual improvement of the liver functions. It is worth noting that Tverdek reported episodes of hyperbilirubinaemia when PCZ C_min is over 1.83 µg/mL, although not attributed to PCZ (Tverdek et al., 2017). In contrast, our study indicates that there is no a clear increase in hepatic damage when PCZ C_min is over 1.83 µg/mL. It is possible that concentration-toxicity relationship shows different profile among different races. Given that the relationship between PCZ C_min and adverse events has yet to be established, further surveillance is warranted. The relationship between PCZ concentrations and mortality rates could not be established since the cause of death could not be identified as fungal infections.

Additionally, we also investigated factors contributing to dose-normalized PCZ concentration variability. Dose-normalized PCZ concentrations were reported instead of actual concentrations to take into account the large variations in PCZ daily doses used when the samples were obtained (Allegra et al., 2017; Jeong et al., 2018; Märtson et al., 2019b). By using this measure, the estimated values could be compared within and between patients without taking variations in the dosage into consideration. No statistically significant differences were detected in age, BMI, digestive disorders, level of serum creatinine, level of γ-Glutamyl transpeptidase, level of alkaline phosphatase, as well as level of total bilirubin or co-administration of metoclopramide in our population. These factors have been analyzed in various studies, obtaining different results depending on the population analyzed (Desplanques et al., 2014; Jeong et al., 2018; Sime et al., 2019). Jeong et al., in agreement with our results, did not observe any association between plasma levels of PCZ and age, BMI, diarrhoea or nausea (Jeong et al., 2018). Conversely, Sime et al., analyzing adult critically ill patients from Australia, described statistically significant differences in concentrations depending on BMI (Sime et al., 2019). Dolton et al. reported coadministration with metoclopramide, underlying diarrhea or mucositis were predictors for lower C_min in haematological malignancies patients (Dolton et al., 2012). However, no such association was observed in our hematological disorders patient. Although PCZ treatment is associated with liver function abnormalities (Boglione-Kerrien et al., 2018), the effect of liver function on PCZ concentrations was not confirmed in our study, which is consistent with the results previously published by Märtson et al. (2019b). Collectively, these results indicate that it is difficult to predict PCZ concentration that we have to monitor trough concentration and adjust PCZ dosage according to the results.

Compared to patients administered PCZ alone, a 25.9% lower PCZ concentrations (P = 0.001) was noted in the patients receiving PCZ co-medicated with PPIs. In a cohort of 43 patients presenting with acute myeloid leukemia, Walsh and colleagues found co-administration with PPI significantly impact PCZ C_min (Walsh et al., 2007). A similar result was identified by Cojutti (Cojutti et al., 2018). After correcting the effects of other factors by multiple linear regression, co-administration of PPI was still a vital factor contributing positively to the variability of PCZ concentration. It is attributed to altered gastric pH caused by H₂ receptor antagonist reducing PCZ absorption, which was confirmed through monitoring of intraluminal PCZ concentrations (Walravens et al., 2011).

Notably, out of the five most frequently recorded concomitant PPIs, lansoprazole and pantoprazole reduced dose normalized plasma PCZ C_min significantly in the univariate analysis. In contrast, omeprazole, the most frequently recorded proton pump inhibitor, showed only minor effects on PCZ concentration. Several controlled studies in healthy volunteers have documented 32% - 37% decrease in the area under the concentration-time curve (AUC) of PCZ with esomeprazole (Sansone-Parsons et al., 2007; Kraft et al., 2014). Nevertheless, an association between low PCZ concentrations and co-administration with esomeprazole (P = 0.179) was not observed in our study, which may be due to the paucity of concentration data of omeprazole combination.

Conflicting results exist regarding the effects of H₂ receptor antagonist on PCZ. The product information states that no PCZ dosage adjustment is needed when co-administered with H₂ antagonists other than cimetidine (Vehreschild et al., 2012). However, Dolton et al. found significantly lower PCZ concentrations in patients receiving H₂ receptor antagonist ranitidine (P < 0.01) (Dolton et al., 2012). Unfortunately, due to the relatively small number of patients concomitant with H₂ receptor antagonist, it is impossible for us to evaluate the impact of H₂ receptor antagonist on PCZ C_min in the present study.

The univariate and multiple linear regression analysis both showed that lower PCZ concentrations were observed with decreasing albumin concentrations, which is in line with previous analysis (Märtson et al., 2019b; Sime et al., 2019). Although CRP level in the current study was negatively correlated with PCZ C_min in the univariate analysis, multiple linear regression analysis did not reveal any statistically significant association, which is consistent with the findings of Märtson et al. (2019a). Furthermore, in this study, CRP and albumin level were identified to be the risk factors for sub-therapeutic C_min (P = 0.049 and P = 0.011, respectively). Therefore, it is necessary to monitor PCZ therapy more frequently during inflammation.

Finally, another unexpected finding in our study is the association between PCZ concentrations and gender. Female patients were more likely to achieve higher PCZ levels in our study. This finding seems contradictory to some studies, of which greater PCZ concentrations in males than females were noted (Allegra et al., 2017; Jeong et al., 2018). On the contrary, no significant association was observed in other studies (Dolton et al., 2012; Märtson et al., 2019a; Oh et al., 2020). This could be due to gender-based differences in CYP-mediated metabolism, sexual hormone influence on drug absorption and differences in fat percent-age in body composition (Beierle et al., 1999). If confirmed in later studies, these findings may help to explain inconsistent results, but more researches incorporating the potential mechanisms should be on the way.

There are several limitations in our study. A limitation of this study is the only limited number of cases, especially in the sub-population analyses, making the results less representative. Confounding factors known to influence PCZ concentrations, e.g., food effects, co-administration of phenytoin and rifampicin or genetic polymorphism of P-gp or UGT (Jeong et al., 2017; Suh et al., 2018), were not further explored in our study attributed to the relatively small sample size. More studies are warranted to further clarify the role of these factors in PCZ variability.

The present study determines the high inter- or intra-patient variability in PCZ C_min in patients with hematological disorders who receive PCZ oral suspension. Gender, albumin concentration and co-administration of PPI were independent factors affecting PCZ Cmin. CRP and co-administration of PPI significantly decreased C_min and probability of the therapeutic window providing treatment benefits. It is necessary to adjust the dosing regimens based on PCZ C_min to obtain an optimal therapeutic response.

The original contributions presented in the study are included in the article/supplementary material; further inquiries can be directed to the corresponding authors.

The study was reviewed by the Human Research Ethics Committee of The First Affiliated Hospital of Zhengzhou University and Ethics approval was obtained (No. 2020-KY-171). Informed consent was waived due to the retrospective nature of this study.

X-JZ and JY designed the clinical trial. M-MJ, Q-WZ, and Z-FQ performed the drug concentration analyses. R-QL and X-KT performed the clinical data collection. M-MJ performed the statistical analyses. All authors contributed to the article and approved the submitted version.

This work was supported by National Natural Science Foundation of China (81803638, 81903704) and Henan Provincial Department of Science and Technology Research Project (182102310330).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.