Safety Standards Needed for Measuring Liquid Medications

standardizing liquid dose measurement
Measuring cup with both TBS (tablespoon) and TSP (teaspoon) markings.

My wife is a registered nurse and I’m a pharmacist. Working with other health professionals in the Philadelphia area, we founded the nonprofit Institute for Safe Medication Practices, the nation’s only organization of pharmacists, nurses, and doctors devoted entirely to safe medication practices. But about 3 years ago, none of that stopped us from nearly harming our 8-year-old granddaughter Sydney with an accidental overdose of Tylenol liquid.

It happened one day when we were babysitting Syd at our house. She had a cold with occasional fever, so we were instructed by our daughter to give her 2 teaspoonfuls of Tylenol (acetaminophen) if she had a temperature above 100. When her fever returned, my wife went to the medicine cabinet to get our bottle of Tylenol as well as a clear plastic dosing cup that I’d placed there some time before. She used the cup to measure what she thought was the embossed line that said “tsp.” Twice she filled the cup and gave it to Syd to swallow, even though Syd did say, “My Mommy doesn’t give me that much.” Syd must be wrong, my wife rationalized, since two teaspoons did seem to be right for a child of her age and weight.  

A few hours later my wife started thinking about what Syd had said. She began to realize that it did seem like a lot of liquid for teaspoonful amounts. She picked up the cup and was shocked to see that what she thought was “tsp.” was actually “tbs.” In other words, she’d given Syd two tablespoons of Tylenol instead of two teaspoons because the abbreviation was hard to make out on the clear cup. A tablespoonful contains about a half ounce, or 15 mL, while a teaspoonful is about 5 mL. We’d accidentally given Syd far too much! My wife called my attention to the overdose and I told her to just not give any more for a time. Syd turned out to be fine, but it was quite a scare to realize how easy it was for a serious error like that to happen.  Had we continued givng Syd the incorrect doses at the approved frequency in product labeling - every 4 hours - she may well have become one of the many children harmed each year in the U.S. by accidental exposure. A large overdose of Tylenol may lead to serious liver damage, which might then require a liver transplant.

This type of dosing mix-up is much more common than you might think. It involves not only mix-ups between teaspoons and tablespoons but also those between milliliters (mL) and teaspoons, between the drops and number of mL and even drops and number of teaspoons. These errors are sometimes even caused by health professionals, such as when a doctor accidentally writes a prescription for a number of teaspoonfuls when, actually, mL was intended - or when a pharmacist accidentally types a label that says teaspoonful when the drug is dosed in mL. Adding to the problem lately has been computer prescription processing technology that, for efficiency, may “default” to teaspoonful amounts when liquids are ordered. If this happens and mL was intended as the dosing unit, doctors and pharmacists have to remember to change the instructions back to mL when teaspoons automatically appear. As you might imagine, this doesn’t always happen. Such mix-ups can obviously lead to both overdoses and under doses, which are often very serious – even fatal. Unlike my wife, many people don’t realize they’ve made this type of dosing error until several overdoses have been given and it may be too late.

That’s exactly what was reported last week by a mother whose child accidentally was given an overdose of antibiotic. The family’s pharmacist accidentally typed a label that gave instructions for her sick child to receive 3.5 teaspoonfuls of antibiotic liquid instead of 3.5 mL that the doctor had ordered on the prescription sent to the pharmacy. The prescription was for 3.5 mL of antibiotic once a day for 10 days.  It was dispensed in a 60 mL bottle. Her daughter was given 3 days’ worth of 3.5 teaspoonful doses.  By the 4th day only one teaspoonful was left in the bottle when it should have lasted 10 days, so the mother called the pharmacy. She found out that the wrong dosage amount had been typed. Unfortunately, since the medication error, her child has experienced voluminous amounts of diarrhea as well as a yeast infection and possibly a fungal infection of the vaginal area.  

This case is just one of over 50 similar overdose mix-ups reported to my organization in recent years, with most resulting in patient harm. Enough is enough! It’s time to standardize to one way of measuring liquids - use of the metric system where volumes are in mL. If we all used the metric system when prescribing, dispensing and administering medications, mix-ups would no longer happen since there would only be a single way to communicate doses. McNeil Consumer Healthcare is one of the companies moving in this direction. Along with standardizing Tylenol Liquid in a single concentration, it is beginning to provide a special dosing device for children that measures in mL to match volumes listed in product labeling of Tylenol and Motrin liquids.  

The Consumer Healthcare Products Association is also working to prevent accidental overdoses in children. The association has published guidelines meant to improve the consistency and standard format for volume measures within the dosing directions for over the counter products. Also, “mL” is recommended for use on accompanying dosing devices that measure OTC oral liquid drug products so they match dosing directions in labeling for children. And the group has  developed manufacturer guidelines to avoid directions that mention tablespoon, cubic centimeters, cc, dram, fluid ounce, Fl. Oz. and dropper(ful). The association advises  member companies to use milliliter as the sole unit of measure in the dosing directions or, alternatively, milliliter and the “teaspoonful” equivalent (e.g., 5 mL [1 tsp]). While they’re at it, I’d also like to see elimination of “pounds” in labeling, especially since drugs are commonly dosed in hospitals using the metric system, with weight in kilograms. We’ve had numerous mix-ups reported due to  conversion errors or when people accidentally weigh a patient in pounds but enter kilogram amounts in the medical record. This throws dosing off by a factor of 2.2 since there are 2.2 pounds per kilogram.  

While these are excellent moves to improve safety, I would like to eventually also see the complete elimination of “teaspoonful” amounts as well as the elimination of the abbreviation “tsp.” Using just “mL” alone would be the best way to eliminate the chance of mix-ups. It may take a generation to fully accomplish these changes and get everyone used to metric dosing, but the time to start is now. Product vendors, doctors and pharmacists who choose to continue to prescribe and dispense liquids using any volumetric method other than mL unknowingly increase the risk of a mix-up. And  abbreviations on labeling or dosing devices, such as TBS, TBSP or TSP, also increases the risk of errors.

One more thing: My granddaughter was right. Mommy didn’t give her so much Tylenol. So listen to yourself - and your patient! If someone tells you something doesn’t seem right or you have your own doubts, always stop what you are doing to investigate. Calling your doctor or pharmacist could save a loved one from harm.

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