Debate on using metric vs. household measures for liquid medicine dosing

I had some interesting responses to my blog last week about the need to go with the metric system of measurement in order to eliminate medication errors with liquid medications. In the blog, I mentioned how doctors, pharmacists, patients and parents sometimes mix up teaspoons and tablespoons, milliliters and teaspoons, or drops and mL, a metric measure of volume.

Standardization is a key component of the way that highly reliable organizations prevent errors. That way everyone is working on the same page and confusion is reduced. 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 dose. The idea is for dosing instructions and measurement to be in mL so that teaspoons don't even enter the thought process, risking a mix-up between the two. Anyway, in my blog, I asked for your feedback and I got it.


On the day that my blog appeared, a distraught mother wrote to tell us that her pharmacist accidentally typed 2 teaspoonfuls (10 mL) twice a day instead of 2 mL twice a day for a prescription for Zantac liquid for her daughter. This led to a five-fold overdose each day, from the end of August until the error was recognized the week before last. Her child had previously been diagnosed with nephrotic syndrome, a kidney disorder, which makes this error even worse because Zantac, a medicine for stomach disorders, is eliminated from the body by the kidneys. Her child was in the process of being examined to ensure that there has not been any long term damage to her organs.

Jimmymack said the simple fact is that our schools don't teach metric. He worried that the vast majority of Americans don't have a clue on what mL means. At the same time, JeffK noted that the canard that schools don't teach the metric system simply doesn't fly. Using multiple and confusing units AND requiring people to translate them is simply a recipe for disaster. If the medicine is measured only in mL and the dosage item is measured only the same way there would be far fewer chances of a mix-up.

One of the responses I received to the blog came to me by e-mail from Georgette Bartell, RN and touched on an aspect I didn’t think about. Ms. Bartell wrote that it would be helpful if new parents were taught to use mL instead of ounces when measuring baby's feedings. She said that baby bottles, formula measurements, and advice regarding amounts per feed should be given in mL with the ounces in parentheses. She works in the neonatal intensive care unit (NICU) at Children's Hospital of Philadelphia so she should know. Parents there learn to keep a log of the amount of milk in mL that mom is pumping from the first day her baby is admitted. The nurses communicate feedings in mL too. She thinks pediatricians should use the metric system with parents for well-baby checks as well as when measuring weights, length, etc. She thinks, as I do, that medical students should get a special lecture on this important safety measure.

Not everyone agrees. I also heard from Dr. Thomas Paparella, an ER physician at Grandview Hospital in Sellersville, PA, who pointed out that everything in medicine today is in the metric system. He thinks the problem is with lay public interaction, because in the US, unlike basically all other countries, our standard unit of measure is still the ounce, pint, etc. He feels that in order to communicate with people you have to speak their language. “Until we sell gasoline and milk in liters we will have to speak to our parents in ounces.” That may be true, but last night I noticed that the wine bottle I was pouring from listed the volume as 750 mL. I’ve never heard anyone complain about that, so at least some Americans must already know how to measure in metric.

Murray Cowan of Philadelphia worried that if teaspoons and tablespoons are no longer used, won’t this mean that medicine bottles will have to have dropper caps or other means of providing proper dosage, which might mean resistance from drug companies? Actually, OTC liquid manufacturers and FDA have agreed that dosing cups, oral syringes or other liquid measuring devices will now accompany liquid products. Also, many pharmacies are already handing out an oral syringe with liquids. All of these devices have mL markings. There may be some hold outs among manufacturers. In those cases we will call them to ask for compliance.

Several of you mentioned that we need to standardize whatever oral dosing devices are used, since right now they are all over the ballpark as far as what is measured, how accurate they are, how they work, etc. I agree with janrx1215who’d like to see the standard be oral syringes with universal bottle adapters. It then would be incumbent pharmacists to train patients on how to use products correctly. This interaction would provide for even those with low health literacy to better understand how to use their medication.

Finally, one of the weirdest things sent to me in the last week was a picture of the manufacturer’s label on Zarbee’s all natural children’s cough syrup. It shows how even companies can make mistakes by confusing teaspoon and mL volumes. The label states “1 tsp 10 mL,” even though a teaspoonful holds about 5 mL. We sent this on to FDA last week, since they have the authority to take action.


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