By guest blogger Michael Cohen:
In 1975 the American Academy of Pediatrics pointed out that using a household spoon to give liquid medication is inaccurate. Yet many Americans rely on teaspoons or tablespoons in their kitchen drawers to measure medicine doses. Doing so could result in an overdose or underdose, which could be significant, especially with certain medications where dosing accuracy is critical or when giving medications to kids.
An accurate teaspoon should hold 5 mL. The strength of oral liquid medications is usually labeled in terms of how much active drug is in 1 mL or 5 mL. For example, an oral liquid antibiotic might be labeled 125 mg per 5 mL, so if the doctor wants the patient to have 125 mg three times a day, the prescription directions would state, “One teaspoonful” to be given that often. Except don’t actually use a teaspoon to measure it!
Household spoons (teaspoons, tablespoons, dessert spoons, soup 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). A milliliter is a metric measure for volume. One mL is about 1/30th of an ounce.
Although some spoon sets you can buy for measuring baking ingredients do include a volumetric measure along with the household measure, these cannot be relied upon to provide accurate dosing. We once purchased a measuring spoon set among those commonly sold in supermarkets and variety stores, which had a ¼ teaspoon size that was also marked 1 mL. If 5 mL is considered one teaspoon, a child who is supposed to take a ¼ teaspoonful dose of a critical liquid medication would receive a 20% underdose. If it indeed contained ¼ teaspoonful, a 25% overdose would result if the prescriber intended only 1 mL. The same manufacturer also sells a plastic measuring spoon set. Here the ¼ teaspoon is marked “1.2 mL.” Checking with the manufacturer, EKCO, they do not intend for their equipment to be used for medication dosing.
Most liquid medications will come with their own measuring devices, like a dosing syringe or spoon or cup. These are fine to use but it’s important to only use the one that comes in the package, keeping it with the product at all times and discarding it when the medication is used up. Errors have occurred when dose cups intended for one product was used with another with a different strength, so measuring a dose would be done differently.
A study published in a medical journal, The Journal of Family Practice, showed that the most accurate way of measuring liquids is with a special oral dosing syringe, using a milliliter scale. These are commonly sold in pharmacies and some even provide one of these for free when dispensing oral liquids. We call them “oral” syringes because they won’t accommodate a needle and can’t be used for injection in hospitals, like a hypodermic syringe can.
My organization, the Institute for Safe Medication Practices (ISMP), supports a medication labeling requirement for oral liquids and syringes to be listed in mL only, not “teaspoons” or tablespoons. That way doctors could prescribe in the same terms to take advantage or oral syringes as measuring devices, allowing more accurate measurement. The Consumer Healthcare Products Association also recommends that manufacturers use milliliter as the preferred unit of measure in the dosing directions and also states that “teaspoonfuls” alone should not be used.
Calibrated droppers that come with some products are another way to measure drugs accurately. However, errors have sometimes happened when a doctor prescribers the dose in “dropperfuls” rather than the amount in mL. We’ve had situations reported where parents have taken that to mean the entire dropper should be filled rather than the upper calibration mark. That’s resulted in drug overdoses with products like iron drops and acetaminophen. As with measuring cups, some have used a dropper supplied for another product, which may also prove inaccurate.