The study involved more than 2,000 parents who were asked to measure the exact dose of liquid medicine needed according to various medicine labels. The medicine labels included directions for three different amounts of liquid medicine. Each amount was listed on the label in either milliliters (mL), teaspoons, or both. For example, the labels that directed parents to measure 5 mL of medicine per dose listed the dose as 5 mL, 5 mL (1 teaspoon), or just 1 teaspoon. To measure these amounts, the parents were given a small dosing cup and two different oral syringes. One of the oral syringes had markings on it for every 0.2 mL. The other oral syringe had markings spaced further apart for every 0.5 mL. The parents were given 9 chances to measure different doses using either a dosing cup or one of the two oral syringes.
During the study, 99% of the parents measured one or more doses that were not the exact amount. There were more errors when measuring 2.5 mL (½ teaspoon) and 7.5 mL (1½ teaspoons) doses of medicine than when measuring 5 mL (1 teaspoon) doses of medicine. Two out of every three mistakes involved measuring out too much medicine. More than 20% of the mistakes were considered large overdoses, which could be very serious in children. The parents made fewer errors as they went through all 9 chances to measure a specific dose, suggesting they got better with practice.
These mistakes happened most often when parents used a dosing cup rather than an oral syringe to measure the dose. Dosing cups greatly increased the risk of errors, especially with smaller doses. In fact, errors were 4 times more likely to occur when measuring the dose using a dosing cup than when using an oral syringe. Parents or caregivers who make mistakes when using dosing cups may be confused about the differences between teaspoons and tablespoons. (One teaspoon equals 5 mL; one tablespoon equals 15 mL.) Some mix up the “tsp” (teaspoon) and “tbsp” (tablespoon) markings because the abbreviations look so similar. Others assume that the entire cup is the correct dose. However, the entire cup typically holds up to 30 mL. Some dosing cups have measurement markings etched in the plastic side of the cup, which is hard to see. Also, when a cup is not held at eye level, it may appear to be filled to the correct level when it is not.
Mistakes also happened more often when there was a mismatch in the way the volume of liquid medicine per dose was stated on the medicine label and on the dosing cup or oral syringe. For example, mistakes happened more often when the instructions on the medicine label listed the dose in teaspoons alone, but the dosing cup or oral syringe had markings on it for mL. Listing doses on medicine labels in teaspoons may also lead to parents/caregivers using household spoons to measure the medicine. The fewest errors occurred when the label listed the dose in mL only and the syringe had measurement markings on it in mL only (not teaspoons or tablespoons). ISMP has long recommended using mL instead of teaspoons or tablespoons when listing doses of liquid medicines. Initially, there were concerns that this might result in confusion because parents may be more comfortable with teaspoons and tablespoons than with unfamiliar mL doses. However, this study suggests that parents measure liquid medicines more accurately when the dose is listed on labels in mL, and when oral syringes with mL markings are used.
See the check it out! column to the right for recommendations to promote accurate measurement of liquid medicine doses.
1.Yin HS, Parker RM, Sanders LM, et al. Liquid medication errors and dosing tools: A randomized controlled experiment. Pediatrics. 2016;138(4):e20160357.