Development of an isavuconazole physiologically-based pharmacokinetic model for adult and pediatric populations.

Isavuconazonium sulfate is the water-soluble prodrug of the active triazole antifungal agent isavuconazole. Isavuconazonium sulfate is approved for the treatment of invasive aspergillosis and invasive mucormycosis in pediatric and adult populations. In the present analysis, an isavuconazole physiologically-based pharmacokinetic (PBPK) model was built and verified in adult and pediatric populations using the Simcyp® simulator. The verified pediatric model was then used to predict the magnitude of DDI risk in pediatric populations vs. adult populations. The simulations conducted were designed to match the observed clinical trials conducted in adults but with pediatric equivalent doses based on clinical guidelines. Based on the results of the analysis, isavuconazole DDI risk was similar between pediatric and adult populations. When the isavuconazole perpetrator DDI simulations were compared to adults, there was a trend of larger geometric mean (GM) AUCinf and Cmax ratios in patients 1 to < 3 years old receiving the 15 mg/kg dose. The GM AUCinf ratio in this study population ranged from 7 to 36% larger than predicted in the adult population. Based on the results of this analysis and literature reports, it is advisable to show greater caution when considering potential DDI in patients < 3-year-old, especially when receiving larger isavuconazonium sulfate doses. In addition, caution should be used in patients < 3 years-old when considering coadministration of isavuconazole with narrow therapeutic index medications such as digoxin and warfarin or medications with large variability in oral bioavailability such as midazolam.