Under the Japanese health insurance system, medicines undergoing therapeutic drug monitoring (TDM) can be billed for medical fees if they meet the specified requirements. In Japan, TDM of vancomycin, teicoplanin, aminoglycosides, and voriconazole, which are used for the treatment of infectious diseases, is common practice. This means the levels of antimicrobial agents are measured in-house using chromatography. This review describes personalized medicine based on the use of chromatography as a result of the current situation in Japan.