Development of Guidelines for Accurate Measurement of Small Volume Parenteral Products Using Syringes

Background: Syringes are commonly used in pharmacy compounding for the measurement of small volumes, especially in the preparation of sterile products for injection and infusion. However, there are no current official guidelines for the proper use of syringes in measuring small volumes. Objective: The purpose of this project was to determine the accuracy and precision of commercially available syringes in measuring small volumes during sterile product preparation to make recommendations for syringe size selection. Methods: To assess precision and accuracy of syringes, 3 separate investigators measured 5%, 10%, or 20% (n = 30 each) of the volume of a 1-, 3-, 5-, 10-, or 20-mL syringe with an attached 18G, 1½" needle by drawing sterile water for injection from a vial. Delivered volumes were measured gravimetrically using an electronic balance and converted to volume using the specific gravity of water (1.0). Accuracy is represented as the mean and standard deviation, while precision is represented as percent relative standard deviation. Differences were assessed using a 1-way analysis of variance with Bonferroni adjustments and significance set at P < .05. Results: Precision and accuracy were highly variable and often significantly (P < .05) different compared to the theoretical volume delivered both within and between investigators. An increased likelihood of unacceptable error (>5%) was observed when less than 20% of the labeled capacity of a syringe was measured. Mean percent error ranged from 1.4% to 18.6%, despite manufacturer specification of ±5% accuracy, suggesting proper technique as a major factor in small-volume measurements. Conclusion: In addition to proper, validated training of syringe users, we recommend that users measure no less than 20% of the indicated volume of the syringe while choosing syringes as close as possible to the desired measurement. When possible, very small volumes should be diluted to meet the minimum volume of the smallest syringe available. Implementation of these recommendations will improve accurate dosing and, ultimately, patient safety.