Metric Measurements Could Prevent Parents' Dosing Errors

Beth Skwarecki

July 17, 2014

Parents who measured liquid medications for their children using teaspoon or tablespoon units were twice as likely to give the wrong dose compared with parents who used milliliter measures, according to a new study published online July 14 in Pediatrics. The investigators argue that errors could be reduced by consistently giving dosing instructions in metric units.

Because labels are often inconsistent in the units of measurement they use, Shonna Yin, MD, from the Department of Pediatrics at New York University School of Medicine in New York City, told Medscape Medical News that providers can help reduce errors by always speaking in terms of milliliters and by providing families with dosing instruments such as marked syringes, droppers, and cups. Parents may encounter different units of measurement on medication labels, in verbal and written instructions, and on prescriptions, Dr. Yin and colleagues write.

In the study, 287 parents whose children (younger than 9 years) had just finished a course of daily oral liquid medication were asked to demonstrate how they had measured the dose at home. The parents included both English (53.3%) and Spanish speakers, and 90% were mothers. The average age of the children was 3.5 years.

Nearly a third (31.7%) of parents, when asked, were incorrect about their child's prescribed dose (defined as giving an answer that deviated from the prescription by 20% or more), although in some cases it had been as long as 8 weeks since the course of medication had ended. Therefore, when assessing the amount parents actually measured, investigators compared this amount with the dose the parents intended to measure, not the amount prescribed.

Parents who used teaspoon or tablespoon units to describe the dose were twice as likely (OR, 2.3; 95% confidence interval [CI], 1.2 - 4.4) to measure out a dose that was more than 20% different from what they intended. They were also 30 times more likely (30.7% vs 1.0%; P < .001) to use a kitchen spoon rather than a marked dosing instrument.

It is a myth that, for example, a kitchen teaspoon always holds a teaspoonful of liquid, Dr. Yin told Medscape Medical News, and she and colleagues note that using terms such as teaspoon and tablespoon "are an inadvertent endorsement for kitchen spoon use." Some measurement errors appeared to be 3-fold errors, suggesting parents are sometimes confusing tablespoons (15 mL) with teaspoons (5 mL).

The investigators compared the units used by parents with those given in the prescription and on the bottle label; the label disagreed with the prescription 36.7% of the time, but only the unit reported by the parent was associated with measurement errors.

Health literacy and language are considered to be risk factors for medication errors. In this study, teaspoon and tablespoon errors were associated with lower degrees of health literacy, as measured by the Short Test of Functional Health Literacy in Adults (P = .002). Adjusted odds of making an error were similar between English and Spanish speakers, although it was only significant for the Spanish speakers (Spanish speakers, P = .045; English speakers, P = .08). All prescriptions were in English.

Health literacy reflects the parent's or patient's ability to read and use health information. "It's an intersection of what the individual brings to the table and what the health care system brings to the table," Dr. Yin said. Parents and patients with lower health literacy or who are less familiar with English may be more prone to confusion, especially when providers and labels use units inconsistently.

To remedy the problem, Dr. Yin and colleagues argue that their results support standardization of milliliter units for all liquid medication labels and prescriptions, despite previous concerns that milliliter measurements would be confusing, as in this study the parents who used milliliters were the least likely to make errors.

"I don't want to put the blame on the patient," Dr. Yin said. "It's a systems problem."

This study was supported by the National Institutes of Health, the Eunice Kennedy Shriver National Institute of Child Health and Human Development, and the National Center for Research Resources. Dr Yin is supported by the National Institutes of Health Loan Repayment Program and the Health Resources and Services Administration. At the time the study was performed, Dr. Yin also was supported in part by the Robert Wood Johnson Physician Faculty Scholars Program. The other authors have disclosed no relevant financial relationships.

Pediatrics. Published online July 14, 2014. Abstract

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