Influence of Viscosity and Consumer Use on Accuracy of Oral Medication Dosing Devices

Background: In response to numerous reports of overdoses with over-the-counter (OTC) liquid medications, the Food and Drug Administration has recommended that all OTC liquid drug products contain a measuring device but provided no recommendation on the type of device to be included. Objective: To evaluate the accuracy of liquid medication dosing devices (cup, dropper, syringe) in dispensing medications of varying viscosity in the laboratory and clinical settings. Methods: This experimental study evaluated dosing device accuracy. A pharmaceutics laboratory was used to evaluate accuracy under ideal conditions and subjects ≥18 years of age were recruited from community pharmacies to evaluate accuracy when used by consumers. Results: In the laboratory setting, the syringe was the most accurate for the more viscous formulations (cherry and grape suspension; 1% error, 1.2% error, respectively), and the dropper was the most accurate for the less viscous formulation (solution; 0.8% error). A volunteer sample of 320 participants was enrolled from the clinical setting. In the clinical setting, the syringe was most accurate, followed by the cup and then the dropper for all formulations (mean error, 2%, 14%, 33%, respectively). The cup was the most likely to overdose (mean, 5.7 mL), while the dropper was most likely to underdose (mean, 3.3 mL). Conclusions: The results of this study suggest that medication viscosity, consumer use, and dosing device contribute to dosing accuracy. The syringe appears to be the most accurate dosing device, accounting for differences in medication viscosity and the impact of consumer use.