Isavuconazonium Sulfate Use in Multi-Modal Management of Invasive Zygomycosis in Four Pediatric Allogeneic Hematopoietic Cell Transplant Patients

Prolonged neutropenia increases risk for lethal invasive fungal infection (IFI) such as Rhizopus. Isavuconazonium sulfate is a new triazole that lacks pediatric dosing recommendations. Clinical courses of 4 pediatric patients with IFI in the peri-allogeneic hematopoietic cell transplantation (alloHCT) period between 2015 and 2017 were reviewed, including previously unreported pharmacokinetic and safety data. IFI included Rhizopus and presumed fungal meningitis. Isavuconazonium sulfate was initiated with a loading dose followed by daily dosing, adjusted to a goal trough >3 ug/mL based on adult literature. This target was achieved at a median of 7 days, demonstrating varying rates of metabolism. Renal insufficiency, electrolyte disturbances, and transaminitis were noted, though attribution was confounded by other alloHCT complications. 1 patient survived infection-free to hospital discharge and 1 of 3 deceased patients had evidence of unresolved IFI (Case 2). Case 2 was subtherapeutic for 39% of the duration of treatment, compared to others at an average of 29%, suggesting this target trough to be clinically relevant. We recommend initiation of isavuconazonium sulfate at 10 mg/kg with a max dose of 372 mg. A loading dose of 10 mg/kg is utilized every 8 hours for 6 doses followed by 10 mg/kg dosing every 24 hours. Monitoring must continue beyond steady state. If early monitoring is not possible, we recommend a first drug level at week 3. If dose increases are required, a partial reload has been more successful instead of increasing daily doses. Further larger studies are needed to demonstrate optimum dosing in pediatric patients.