The physical compatibility of caspofungin acetate injection with selected other drugs during simulated Y-site coadministration was evaluated by visual observation and turbidity measurement. Five-milliliter samples of caspofungin acetate 0.7 mg/mL in 0.9% sodium chloride injection were combined with 5 mL of 67 other drugs including antineoplastics,analgesics, anti-infectives, and supportive care drugs, undiluted or diluted in 0.9% sodium chloride injection or 5% dextrose injection, and with a parenteral nutrition admixture. Visual examinations were performed with the unaided eye in normal laboratory fluorescent light and with a Tyndall beam (high-intensity monodirectional light beam) to enhance visualization of small particles and low-level turbidity. The turbidity of each sample was measured as well. The sample mixtures were evaluated immediately and at 1 and 4 hours after preparation. Nineteen of the drugs tested and the parenteral nutrition admixture were incompatible with caspofungin acetate 0.7 mg/mL during the 4-hour observation period. The remaining drugs were compatible for at least 4 hours. Gross precipitation or turbidity changes visible in normal diffuse room light with the unaided eye occurred with 18 drugs and with the parenteral nutrition admixture. Microprecipitation of particulates not visible with the unaided eye occurred with cytarabine. The measured turbidity of the caspofungin acetate control solutions and the compatible test samples remained essentially unchanged throughout the observation period. In combination with caspofungin acetate, 48 drugs and a parenteral nutrition admixture were considered to be physically compatible. In contrast, 19 drugs with the parenteral nutrition admixture exhibited frank precipitation or microparticulate formation within 4 hours and should not be simultaneously administered via Y-site with caspofungin acetate.