Measurement mishaps with liquid medicines

Unlike medicines for adults, medicines for babies and young children often come in a liquid form. Thus, parents and caregivers must measure the correct amount of liquid medicine before giving each dose to their child. Many over-the-counter (OTC) liquid medicines come with a plastic dosing cup, oral syringe, or dropper to help measure a dose. A pharmacist may provide a dosing cup or oral syringe with liquid prescription medicines. However, a study published in October 20161 shows that parents often struggle with measuring the exact dose of liquid medicine and make errors frequently.

The study

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.

To accurately measure doses of liquid medicines, consider these recommendations:

• Use oral syringes with mL markings. Oral syringes are considered the gold standard when accurate measurement of the medicine dose is critical. Healthcare professionals use oral syringes to accurately measure medicine doses; so should parents. The oral syringe should have mL markings on it and preferably no other markings (e.g., teaspoons or tsp). If your child’s medicine comes with a dosing cup, ask your pharmacist for an oral syringe for you to use instead, particularly if a small volume of the medicine is needed for each dose.
• Evaluate the dropper when provided. If your child’s medicine comes with a dropper, check if the markings are easy to see and understand. If not, ask your pharmacist to provide a small-volume oral syringe to replace the dropper.
• Make sure markings match the needed dose. Be sure the oral syringe markings match the volume of medicine that is needed to measure each dose. For example, if a dose of 0.5 mL is needed, the oral syringe should have markings that correspond to 0.5 mL.
• Never use a household spoon. To promote dosing accuracy, both the American Academy of Pediatrics (AAP) and the US Food and Drug Administration (FDA) discourage using kitchen teaspoons or tablespoons, which vary widely in volume.
• Inspect instructions on labels. Before leaving the pharmacy with a prescription or OTC liquid medicine, check the label. If the directions for use include teaspoon or tablespoon measurements only, verify the mL amount of each dose with the pharmacist. Also ask the pharmacist to relabel any prescription medicine to include the mL amount of each dose.
• Verify dose measurement with a pharmacist. Whether your child’s medicine is an OTC (no prescription needed) or prescription medicine, it is always best to verify with your pharmacist that you know how to measure the correct dose. Ask your pharmacist for a demonstration, and then show the pharmacist how you will measure each dose to verify accuracy. This is especially important for doses that are not measured in whole numbers (e.g., 2.5 mL, 7.5 mL).

Reference
1. Yin HS, Parker RM, Sanders LM, et al. Liquid medication errors and dosing tools: A randomized controlled experiment. Pediatrics. 2016;138(4):e20160357.

Article reviewed and updated August 25, 2021