A New Dosing Regimen for Posaconazole Prophylaxis in Children Based on Body Surface Area

Hematological Malignancy

chemotherapy, stem cell transplantation

A new prophylactic posaconazole dosing regimen of 120mg/m² tid is evaluated pharmacologically in children 13 years and younger, suffering from a hematologic malignancy.

Invasive fungal infections (IFI), especially candidiasis and aspergillosis, are a serious threat to immunocompromised pediatric patients. Because diagnosis of IFI in pediatric patients is difficult, due to the lack of specific clinical and radiological signs and the low sensitivity of blood cultures, antifungal prophylaxis would largely optimize management of IFI in this setting. However, antifungal prophylaxis remains a matter of debate, as no clear consensus has yet been reached about the optimal drug. Very limited pediatric data are available, and current guidelines are mainly based on extrapolation of adult data. Fluconazole remains the drug of choice in many centers, despite its non-mould active spectrum. Itraconazole, liposomal amphotericin B and nebulized lipid-formulations of amphotericin B are often used off-label, although neither their pharmacokinetics (PK), nor their efficacy and safety have been documented in a proper way. Voriconazole is registered for children older than 2 years of age, mainly in the treatment setting. Moreover, its extremely variable PK profile, uncertainty about adequate exposure and risk for hepatotoxicity and neurotoxicity do not favor the use of voriconazole in this setting. Finally, micafungin only has low recommendation in the prophylactic setting, due to the possible risk of liver tumours. Posaconazole would be the ideal antifungal drug to be used prophylactically in children for many reasons. It has a broad spectrum of activity, including emerging moulds like Aspergillus spp. and Zygomycetes. It has shown to be superior over fluconazole and itraconazole in preventing IFI in adults and it has a favorable safety profile, with nausea and vomiting being the most frequently encountered adverse events. However, lack of pharmacokinetic (PK) data in children younger than 13 years of age, results in only a marginal recommendation in current guidelines \[8\]. Little information is available about the correct dosing regimen of the available oral suspension in young pediatric patients, and similar to what is observed in adults, often very low posaconazole plasma concentrations (PPCs) are being measured. Therefore, therapeutic drug monitoring (TDM) is recommended to reach adequate PPCs above 0.5mg/L or 0.7 mg/L followed by increasing the dose as needed. In this study, the pharmacokinetics of a newly introduced dosing regimen for posaconazole oral suspension is investigated, based on body surface area (BSA), used prophylactically in immunocompromised children under the age of 13. Pediatric patients, admitted to the hospital to receive chemotherapy or hematopoietic stem cell transplantation are treated prophylactically with posaconazole 120mg/m² tid. At steady state (after at least 7 days of posaconazole treatment), 9 plasma samples are collected in these patients to calculate the area under the curve and other relevant PK parameters as maximum and minimal plasma concentrations, volume of distribution, halflife and clearance rate. Finally, these results will be compared to adult data in literature to evaluate whether 120mg/m² tid an adequate dosing regimen in children.

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