2: Liquid Pediatric Medication Dosing Cups Are Inaccurate

Article Outline

• Study Objectives
• Methods
• Results
• Conclusions
• Copyright

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Study Objectives 

To compare the accuracy of over the counter pediatric liquid medication measuring cups with a standard graduated cylinder.

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Methods 

In this prospective, observational study, common over the counter pediatric liquid medications for the treatment of allergies, cold and flu symptoms, and general pain were purchased at a pharmacy. Two investigators independently measured both 2.5 and 5 mLs (one measuring cup only allowed 5 mL and 7.5 mL measurements) of each medication or colored water into the dosing cup provided with each medication. This liquid was then poured into a standard 10 mL graduated cylinder and the measurement recorded. Both investigators were blinded to the other's measurements. All cylinders and cups were thoroughly washed and allowed to dry between measurements. A Bland-Altman plot was constructed and the bias and 95% limits of agreement calculated to assess inter-rater agreement between the measurers. Matched pairs analysis was used to test whether or not observed differences in measurements between the dosing cup and the cylinder were statistically significant with an alpha of 0.05 selected as the threshold for statistical significance. The average differences observed between the cups and cylinders with 95% confidence intervals (CI) were calculated to assess the precision of the estimate.

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Results 

Seven dosing cups that came with seven over the counter medications were tested. Both investigators did not significantly differ (p = 0.15) in their measurements (average bias of −0.1 mL; 95% limits of agreement −0.6-0.8). Overall, when water was tested against the cylinder for all seven dosing cups, the cylinder provided a measurement 0.63 mL (95% CI 0.42-0.86) greater than the dosing cup (p < 0.0001). Results were similar when using the medication that came with each dosing cup, with the cylinder providing an average measurement 0.33 mL (95% CI 0.15-0.52) greater than the measuring cup (p = 0.0012). When excluding the two most accurate dosing cups from the analysis the average difference was 0.54 mL (95% CI 0.37-0.72) for medication (p < 0.0001) and 0.91 mL (95% CI 0.73-1.10) for water (p < 0.0001). For one medication, an average difference of 1.15 mL more of the medication in the cylinder versus the cup was observed. When using water, the difference for this cup still averaged 1.05 mL more of liquid in the cylinder.

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Conclusions 

Common over the counter pediatric liquid medication measuring dose cups may provide a larger dose of medication than intended. Given that one previous study demonstrated that subjects often measure a larger than intended dose using a dosing cup, these differences may be magnified in actual practice. The potential clinical impact of this finding should be investigated.