Abstract
Serum protein binding of micafungin (MCFG), which has anti-fungal effects also on non-candida fungi such as Aspergillus fumigatus, is 99.8%. In this study, we defined the mechanism by which MCFG exerts its action despite high protein binding properties. Lowest concentration of MCFG needed for suppression in the growth of Candida albicans was determined by two methods: the minimum inhibitory concentration (MIC) and disk methods. In each method, the agent was diluted either by RPMI1640/3-(N-morpholino) propanesulfonic acid (MOPS) (RPMI) or inactivated serum, which simulated clinical situation. Unexpected low MIC (1μg·ml−1) was found in serum-diluted samples: if consider serum protein binding, 30 folds higher concentration than those obtained would be required. The disk method, determining concentration plus exploring diffusion factors of the agent, revealed the results supporting those in MIC method. These results indicate that despite high protein binding in vitro, MCFG exerts anti-fungal effects through possible mechanisms, such as its weak protein binding, which needs to be clarified in the future.
