A guideline for the preparation of peripherally administered antibiotics in fluid-restricted patients was developed. A maximum osmolality of 560 mOsmol/kg was selected since this corresponds to the theoretical osmolality of dextrose 5% in NaCl 0.9%, a solution commonly administered peripherally without significant incidence of phlebitis. Percentage concentrations corresponding to 560 mOsmol/kg of 26 intravenous antibiotics were calculated using sodium chloride equivalents. The antibiotics were reconstituted using sterile water, dextrose 5%, and NaCl 0.9% to provide an osmolality of 560 mOsmol/kg. The resulting solutions were measured for osmolality using a freezing-point depression osmometer. A total of 78 solutions were prepared and measured in triplicate. Of the 78 measured osmolalities, 67 (86 percent) were within 20 percent of the desired 560 mOsmol/kg. Only two osmolalities were more than 10 percent above the projected value. The percentage concentrations of 26 antibiotics in three solutions corresponding to 560 mOsmol/kg are presented. A method is also provided for tailoring concentrations to achieve desired osmolalities other than 560 mOsmol/kg.