Evaluation of Posaconazole Serum Concentrations from Delayed-Release Tablets in Patients at High Risk for Fungal Infections.

The purpose of our study was to determine the frequency of patients who achieved a therapeutic drug level after receiving posaconazole (PCZ) delayed-release tablets (DRT) for prophylaxis or treatment of invasive fungal infections (IFIs) and to examine the effect of demographic traits and treatment characteristics on PCZ serum levels. A retrospective single-center study was conducted on high-risk inpatients at the University of Washington Medical Center (UWMC) that had received PCZ and obtained PCZ serum levels for either treatment or prophylaxis between 1 August 2014 and 31 August 2015. High-risk patients were defined as those undergoing chemotherapy for a primary hematologic malignancy and those undergoing hematopoietic cell transplantation (HCT) or solid organ transplantation. Serum trough concentrations of ≥700 μg/liter and ≥1,000 μg/liter were considered appropriate for prophylaxis and treatment, respectively. The most frequent underlying medical condition was a hematological malignancy (43/53, 81%). Twenty-six of 53 patients (49%) received PCZ for prophylaxis; the rest received PCZ for treatment. A total of 37/53 (70%) patients had PCZ serum levels of ≥700 μg/liter regardless of indication, including 22/26 (85%) that received PCZ for prophylaxis. Of the patients that received PCZ for treatment, only 12/27 (44%) had PCZ serum levels of ≥1,000 μg/liter. The odds of having therapeutic PCZ serum levels were not statistically different in patients with a weight of ≥90 kg, a diarrhea grade of ≥2, a mucositis grade of ≥2, or poor dietary intake. However, the odds of having therapeutic PCZ serum levels was 5.85 times higher in patients without graft-versus-host disease (GVHD) treatment than in those with GVHD treatment. Four patients on prophylaxis (15%) developed breakthrough IFIs, one of which had a subtherapeutic level. We concluded that the use of PCZ DRT provided adequate concentrations in only 70% of our patients and that recommended dosing may lead to insufficient levels in patients treated for IFIs. Lower concentrations noted among high-risk patients with GVHD suggest a need for prospective studies evaluating therapeutic drug monitoring and/or dose adjustments among these patients.