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

Prolonged neutropenia increases the risk for lethal invasive fungal infections (IFIs) such as those caused by Rhizopus species. Isavuconazonium sulfate is a new triazole that lacks pediatric dosing recommendations. Clinical courses of 4 pediatric patients with IFIs in the peri-allogeneic hematopoietic cell transplantation (alloHCT) period between 2015 and 2017 were reviewed. The reviews included previously unreported pharmacokinetic and safety data, and the IFIs included Rhizopus. Isavuconazonium sulfate was initiated with a loading dose followed by daily dosing, adjusted to a goal trough concentration of >3 mg/L 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, although attribution was confounded by other alloHCT complications. One patient survived infection-free to hospital discharge and 1 of 3 deceased patients had evidence of an unresolved IFI (case 2). Case 2 was subtherapeutic for 39% of the duration of treatment, compared with others at an average of 29%, suggesting this target trough to be clinically relevant because case 2 demonstrated positive sinus and nasal cultures for Rhizopus on autopsy. We recommend initiation of isavuconazonium 10 mg/kg with a maximum dose of 372 mg. A loading dose of 10 mg/kg is used 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.