We need to go metric to prevent errors with oral liquids

Nothing riles me more than when a report reaches us through our medication error reporting program where a child accidentally gets an overdose of liquid medication due to nothing more than simple confusion between dosage units. Doctors, pharmacists and parents mix up teaspoons and tablespoons, milliliters and teaspoons, or drops and mL, a metric measure of volume. This is one error that should not be happening at all. We know what’s needed to put an end to it.

In June I wrote about a pharmacist’s labeling error that gave instructions for a young child to receive 3.5 teaspoonfuls a day of antibiotic liquid instead of 3.5 mL that the doctor had ordered. The child experienced voluminous amounts of diarrhea, a yeast infection, and possibly a fungal infection of the vaginal area. In that same article I described how my own wife, a seasoned RN who works with me on medication safety efforts, misread the readings on a liquid dosage cup. She read TBSP (tablespoonful) as TSP (teaspoonful) and gave our granddaughter Sydney 2 tablespoonfuls of Tylenol liquid instead of 2 teaspoonfuls. Fortunately, we caught the error before the next dose and things turned out fine.

I get annoyed about the whole situation because we first reported on the confusion of teaspoonfuls and mL in 2000. In 2009 we issued a call for practitioners to move to sole use of the metric system (mL) for measuring over‐the-counter (OTC) and prescription oral liquid doses. But mix‐ups continue to cause serious injury in children and adults. ISMP has received more than 50 reports of mL‐teaspoonful errors alone, including cases where injuries required treatment or hospitalization.

Why did we call for sole use of the metric system anyway? One reason is that dosage strengths of medicines use the metric system. For example, an oral liquid antibiotic might be labeled 125 mg per 5 mL. Syringes and dosing cups that come with oral liquids also are labeled in mL. Also, dosage calculations are made using metric weight in kilograms and mg or mL.

With medicines, accuracy is obviously important. An accurate teaspoon should hold 5 mL. But household spoons are not standardized and deliver only an approximate dose at best. Depending on their size, a typical household teaspoon can hold between 3 and 7 milliliters (mL). One mL is about 1/30th of an ounce. So if the doctor wants the patient to have 125 mg three times a day, the prescription directions should state, “Five mL three times a day.”

My organization, the Institute for Safe Medication Practices (ISMP), is once again asking prescribers, pharmacists, other healthcare professionals, manufacturers and computer system vendors to only use metric measurements in prescription directions. Our board of trustees took this step after careful deliberation, in order to better protect patients from harmful errors. It also gives providers a greater level of comfort and confidence when calculating and administering doses of medication.

Other organizations, such as the US Food and Drug Administration, Consumer Healthcare Products Association, and Centers for Disease Control and Prevention have also drawn attention to use of the metric system for oral liquids or suggest including both measurements with drug dosing instructions. We’ve met with each of these groups to stress that use of the metric system alone when prescribing, dispensing, and administering medications would prevent mix‐ups because there would only be one method used to communicate and measure doses.

I have often heard my pharmacist colleagues express doubts about getting consumers to go completely metric for measurement of medicine doses. However, I don’t think it’s a stretch at all. Several companies, including McNeil Consumer Healthcare, are already moving in this direction by standardizing their acetaminophen infant and children’s oral liquid medications in a single concentration and developing dosing devices that measure in mL. Many other companies are following suit. I have no doubt that you’ll be able to do your part.

We are also asking pharmacists to take steps to ensure patients have an appropriate device to measure oral liquid volumes in milliliters. They’ll need to coach patients on how to use and clean measuring devices and have patients show them they know how to measure by asking them to demonstrate their understanding.

We realize that a transition period may be necessary during which the household measure can be listed in parentheses immediately following the metric measure—e.g., 5 mL (one teaspoonful). But still, it’s time that authorities set a date for full conversion. Solving this common reason for medicine overdoses in children should be the goal for all of us. I’d love to hear from you about your thoughts on the matter.

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