Variability and exposure-response relationships of isavuconazole plasma concentrations in the Phase 3 SECURE trial of patients with invasive mould diseases

Objectives This analysis evaluated the variability of isavuconazole plasma concentrations between subjects and between sampling times, and assessed their relationship to outcomes for subjects with invasive fungal disease (IFD) in the SECURE trial. Methods Isavuconazole-treated subjects received 372mg of isavuconazonium sulphate (corresponding to 200mg of isavuconazole) three times daily for 2days, then once daily. Plasma samples were collected after day 4 and analysis sets were constructed as follows: analysis set 1 included all samples from subjects with proven/probable/possible IFD who received 1 dose of isavuconazole; analysis set 2 included samples from subjects in analysis set 1 who had provided >1 sample; and analysis set 3 included samples from subjects in analysis set 1 with proven/probable invasive aspergillosis. Assessments included overall distributions of plasma concentrations and variability between samples (analysis sets 1 and 2) as well as relationships to outcomes [all-cause mortality (day 42), overall response (end of treatment) and treatment-emergent adverse events; analysis sets 1 and 3]. Results Analysis sets 1, 2 and 3 included samples from 160, 97 and 98 subjects, respectively. Trough concentrations for each were distributed similarly [mean (SD): 3406.6 (1511.5), 3495.6 (1503.3) and 3368.1 (1523.2)ng/mL, respectively]. The mean coefficient of variation between samples in analysis set 2 was 23.2%; differences between concentrations in first samples and subsequent samples were <2-fold for 85/97 subjects. In quartiles of subject data, no concentration-dependent relationships were observed for efficacy or safety. Conclusions Plasma concentrations of isavuconazole were reasonably consistent between subjects and sampling times, and were not associated with differences in outcomes.