We can do better: a fresh look at echinocandin dosing

First-line antifungal therapies are limited to azoles, polyenes and echinocandins, the former two of which are associated with high occurrences of severe treatment-emergent adverse events or frequent drug interactions. Among antifungals, echinocandins present a unique value proposition given their lower rates of toxic events as compared with azoles and polyenes. However, with the emergence of echinocandin-resistant Candida species and the fact that a pharmacometric approach to the development of anti-infective agents was not a mainstream practice at the time these agents were developed, we question whether echinocandins are being dosed optimally. This review presents pharmacokinetic/pharmacodynamic (PK/PD) evaluations for approved echinocandins (anidulafungin, caspofungin and micafungin) and rezafungin (previously CD101), an investigational agent. PK/PD-optimized regimens were evaluated to extend the utility of approved echinocandins when treating patients with resistant isolates. Although the benefits of these regimens were apparent, it was also clear that anidulafungin and micafungin, regardless of dosing adjustments, are unlikely to provide therapeutic exposures sufficient to treat highly resistant isolates. Day 1 probabilities of PK/PD target attainment of 45.6% and 65.7%, respectively, were achieved at the C. glabrata MIC90 for these agents (0.12 and 0.03 mg/L, respectively). However, evaluations of rezafungin demonstrated high probabilities of target attainment over 4 weeks of therapy (100%) after administration of a single-dose regimen at the MIC90 of 0.06 mg/L. This signals that although existing therapies are not optimal to treat resistant organisms, more potent new echinocandins (relative to achievable drug exposures) may be on the horizon.