In vitro synergy of caspofungin with licensed and novel antifungal drugs against clinical isolates of Fusarium spp.

Combinations of caspofungin (CAS) with amphotericin-B (AMB), voriconazole (VRC), terbinafine (TRB) and tacrolimus (FK-506) were tested in vitro with 10 Fusarium isolates. MIC and minimal effective concentrations (MEC) were investigated in accord with the CLSI methodology. Drug interactions were assessed by the fractional inhibitory concentration index (FICI). Synergy occurred in 10/10, 9/10, 7/10 and 4/10 isolates with CAS/FK-506, CAS/TRB, CAS/AMB and CAS/VRC, respectively. Caspofungin MECs reached clinically attainable concentrations with FK-506 and TRB. Hyphal length and DiBAC staining demonstrated enhanced inhibition and killing with CAS/FK-506 and CAS/TRB. The combination of CAS/TRB and CAS/FK-506 is strongly synergistic in vitro against Fusarium spp. Our finding should be further studied in animal models of invasive infections caused by this fungus.