OTC Pediatric Dosing Cups Often Marked to Give Inaccurate Doses

Nancy A. Melville

October 06, 2010

October 6, 2010 (Las Vegas, Nevada) — Cups to measure pediatric liquid medication dose, commonly sold with over-the-counter medications, often are marked inaccurately, potentially providing a larger dose than is intended or recommended, according to research presented here at the American College of Emergency Physicians 2010 Scientific Assembly.

Researchers independently measured 2.5 and 5.0 mL doses of water and medication according to markings on 7 over-the-counter medication dose cups, and then poured the contents into a standard 10 mL graduated cylinder and recorded the measurement.

Overall, the results on the accurate cylinder showed measurements that were an average of 0.33 mL greater than the measuring cup (95% confidence interval [CI], 0.15 - 0.52; P = .0012).

When water was tested against the cylinder for all 7 dosing cups, the cylinder measurement was 0.63 mL more than the dosing cup (95% CI, 0.42 - 0.86; P < .0001).

Lead author Allison M. Tadros, MD, assistant professor and assistant residency director of emergency medicine at West Virginia University School of Medicine in Morgantown, noted that the inaccuracies occurred in the careful context of a scientific study; in the hands of actual users, the measurements could be even more inaccurate.

"We were taking our time and being careful, but we all know that in the context of treating a screaming child at 3 in the morning, most are not taking the time to really measure accurately."

For the study, Dr. Tadros and a colleague were blinded to each other's measurements. The investigators did not significantly differ in their measurements (average bias, −0.1 mL; 95% limits of agreement, −0.6 - 0.8; P = .15).

When the researchers excluded the 2 most accurate dosing cups from the analysis, the average difference was 0.54 mL for medication (95% CI, 0.37 - 0.72; P < .0001) and 0.91 mL for water (95% CI, 0.73 - 1.10; P < .0001).

One cup studied measured an average of 1.15 mL more of the medication than the cylinder. With water, the difference averaged 1.05 mL more than the cylinder.

Dr. Tadros said that the type of dosing cup and the color of the medicine made a difference.

"We found that some of the cups were embossed with the measurements, instead of printed, and it was much harder to make the measurement on the embossed cup. If the medication was clear, measuring was also more difficult."

She noted that a study in 2008 asked volunteers to measure 5 mL of acetaminophen (Tylenol) in a dosing cup. When the researchers pulled the medicine into a syringe, and they found that, on average, they were getting 6.3 mL instead of 5 mL.

For a 1-time dose, the discrepancies might not have a clinical significance, but they could be problematic in longer-term use, Dr. Tadros noted.

"The numbers may seem low, but keep in mind that some of them are being dosed multiple times a day," she said. "So it could be more of a clinical consequence over the course of a day or several days, when you're giving more medication than you should with every dose."

The study sheds light on potentially important flaws in the dosing measurements on pediatric medication cups, but the clinical implications of the discrepancies remain to be seen, according to Jill M. Baren, MD, director of pediatric emergency medicine education in the Department of Emergency Medicine at the Hospital of the University of Pennsylvania in Philadelphia, and moderator of the session at which Dr. Tadros presented her findings.

"This is the first study to raise the point that inaccurate dosing of medication using over-the-counter medicine cups can occur. However, at this point, we can't really say with certainty that this translates to anything clinically meaningful. This study was not designed to demonstrate that," said Dr. Baren.

"The researchers suggest that prior studies have shown that parents already tend to err on the side of giving more liquid. Therefore, discrepancies in a small child could have potential clinical ramifications," she added.

Dr. Tadros and Dr. Baren have disclosed no relevant financial relationships.

American College of Emergency Physicians (ACEP) 2010 Scientific Assembly: Abstract 2. Presented September 28, 2010.

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