Dose escalation studies with caspofungin against Candida glabrata

Echinocandins are recommended as first-line agents against invasive fungal infections caused by Candida glabrata, which still carry a high mortality rate. Dose escalation of echinocandins has been suggested to improve the clinical outcome against C. glabrata. To address this possibility, we performed in vitro and in vivo experiments with caspofungin against four WT C. glabrata clinical isolates, a drug-susceptible ATCC 90030 reference strain and two echinocandinresistant strains with known FKS mutations. MIC values for the clinical isolates in RPMI 1640 were ≤0.03 mg l^-1 but increased to 0.125–0.25 mg l^-1 in RPMI 1640+50% serum. In RPMI 1640+50% serum, the replication of C. glabrata was weaker than in RPMI 1640.Caspofungin in RPMI 1640 at 1 and 4 mg l^-1 showed a fungicidal effect within 7 h against three of the four clinical isolates but was only fungistatic at 16 and 32 mg l^-1 (paradoxically decreased killing activity). In RPMI 1640+50% serum, caspofungin at ≥1 mg l^-1 was rapidly fungicidal (within 3.31 h) against three of the four isolates. In a profoundly neutropenic murine model, all caspofungin doses (1, 2, 3, 5 and 20 mg kg^-1 daily) decreased the fungal tissue burdens significantly (P<0.05–0.001) without statistical differences between doses, but the mean fungal tissue burdens never fell below 10⁵ cells (g tissue)^-1.The echinocandin-resistant strains were highly virulent in animal models and all doses were ineffective. These results confirm the clinical experience that caspofungin dose escalation does not improve efficacy.