Use of Penicillin Skin Testing as an Antimicrobial Stewardship Initiative: Clinical and Economic Evaluation at a Community Health System

Background. Isavuconazole (ISA) is a once-daily, extended-spectrum triazole approved for treatment of invasive aspergillosis and mucormycosis. The pharmacokinetic profile, daily dosing, lack of therapeutic drug monitoring (TDM) and reduced cost make ISA a promising option for use as prophylaxis for invasive fungal infections (IFIs). We report our experience with use of ISA for prophylaxis of IFI in high-risk hematologic malignancy patients. Methods. In August 2016, ISA replaced posaconazole (POS) for IFI prophylaxis at our 576-bed academic medical center in order to contain drug costs. ISA prophylaxis was restricted to patients with the following high-risk criteria: refractory or relapsed acute myeloid leukemia, myelodysplastic syndrome or graft-vs.-host disease receiving high-dose steroids. We electronically identified all drug orders for ISA prophylaxis between August 2016 and March 2017; patient and encounter identifiers and start and stop dates were electronically extracted. Additional clinical data was collected via chart review. ISA costs were calculated using ISA days of therapy (DOT) and current ISA acquisition costs; POS costs were extrapolated from ISA DOT and calculated using current POS acquisition costs. Data were summarized using descriptive statistics; drug costs were compared using paired t-test. Results. 113 patients received ISA for a total of 2610 patient-days of therapy. Mean age was 53 years; 22 (12.9%) patients were admitted to the intensive care unit during therapy. Intravenous ISA accounted for 731 DOT, and oral ISA for 1679 DOT. TDM was performed 10 times and the median ISA level was 5.3 μg/mL (IQR 2.9 – 7.2). The switch resulted in a mean cost savings of $119.11 per DOT compared with extrapolated POS costs (P < 0.01). Upon discharge, insurance denied coverage of ISA prophylaxis in 14% of patients, and 11% of patients received an alternative antifungal prophylaxis agent. Grade 2 liver injury possibly related to ISA occurred in 9% of patients. Conclusion. At our institution, utilizing ISA for IFI prophylaxis resulted in cost savings relative to POS. Lack of insurance coverage for ISA at discharge remains a major challenge. Further study should assess infectious outcomes with ISA prophylaxis. Disclosures. J. S. Lewis II, Merck & Co.: Consultant, Consulting fee.