The objective of this study was to evaluate the physical compatibility of micafungin injection with selected other drugs during simulated Y-site co-administration. Physical stability was assessed by both visual observation and turbidity measurement. Micafungin in 0.9% sodium chloride injection was combined with each of 48 other drugs, including antineoplastics, analgesics, anti-infectives, and supportive care drugs undiluted or diluted in 0.9% sodium chloride injection, and with a parenteral nutrition admixture. Visual examinations were performed with the unaided eye in fluorescent light and by using a Tyndall beam, and the turbidity of each sample was measured. The samples were evaluated immediately after mixing and again 1 and 4 hours after preparation. Twenty-nine of the drugs tested were found to be compatible for at least 4 hours. The measured turbidity of the micafungin control solutions and the compatible test samples remained essentially unchanged throughout the study. The other 19 drugs exhibited frank precipitation, microparticulate formation or unacceptable increases in turbidity within 4 hours of mixture with micafungin and thus should not be administered simultaneously via Y-site with micafungin.