BACKGROUND: Both overmedication and undermedication can be potentially life threatening. If the actual volume of a 100-mL intravenous bag used to mix dopamine solutions is greater than the labeled volume, overdilution of medication can occur, resulting in an ineffective hemodynamic response in patients and thus an unintended adverse drug event. OBJECTIVES: To determine the actual fluid volumes of 100-mL intravenous bags, compare the actual volumes of 100-mL bags from the 3 major manufacturers of intravenous bags, and determine if the excess volume is sufficient to cause a clinically significant overdilution of dopamine. METHODS: A comparative descriptive design was used. The volumes of 162 intravenous bags of 100 mL of 5% dextrose in water (32 lot numbers with various expiration dates) were measured. Visual volume was confirmed by using a 250-mL graduated cylinder. Volume by weight was determined with a calibrated laboratory-quality electronic scale. On the basis of a mathematical model, any overfill greater than 110 mL was considered clinically significant. RESULTS: The difference between actual and labeled volumes was statistically and clinically significant. Mean visual volume was 110.20 mL (range, 107-114 mL). Mean weighed volume was 109.26 mL (range, 106.15-112.09 mL). The fluid volumes among bags from the 3 major IV companies differed significantly (P < .001). CONCLUSIONS: The overfill in sufficient numbers of 100-mL intravenous bags was enough to cause clinically significant overdilution of dopamine. When dopamine or other vasoactive medications are mixed, either an in-line buret or premixed bags of the drugs should be used to prevent an unintended adverse drug event.