Medicine and the Metric System

Allow me to present my main point upfront: we are endangering our health by not adopting the metric system in this country.

Prescriptions are written in metric units. Conversions (and possible errors) are made at the pharmacy.

Doctors write prescriptions in metric units. Conversions (and potential errors) are made at the pharmacy.

Let me offer up a couple of examples that hopefully makes this clear. It’s important to understand that the medical field depends on metric units (as does most of science, for that matter). If healthcare workers talk in metric units and the public at large rely on U.S. customary units there is bound to be confusion and misunderstandings. That’s best avoided where your heath is concerned since the consequences could be dire.

Metric unit dosing is more precise

Last year Pediatrics (Official Journal of the American Academy of Pediatrics) published an article called “Unit of Measurement Used and Parent Medication Dosing Errors.”1 One of the article’s bottom lines:

Parents who used milliliter-only unit made fewer dosing errors than those who used teaspoon or tablespoon units. Moving to a milliliter-only standard could reduce confusion and decrease medication errors, especially for parents with low health literacy and non-English speakers.

While a minor mistake (whether too much or too little medication) might not make a huge difference for an otherwise healthy adult, these errors can be magnified for babies or those whose health is already compromised.

Most of our teaspoons and tablespoons are meant for eating, not dosing

No on should use "silverware" as substitutes for measuring teaspoons and tablespoons for medicine to avoid dosing errors.

No on should use “silverware” as substitutes for measuring teaspoons and tablespoons for medicine if they want to avoid dosing errors.

Another issue brought up in the piece was that the use of teaspoon and tablespoon employed for liquid medicines “may endorse kitchen spoon use.” I don’t know about you, but I have three sets of measuring spoons and many more spoons that I use for eating commonly referred to as “teaspoons” and “tablespoons.” The problem is, it’s the eating spoons that are often used to measure medicines. (Yes, I used to do that too, without even thinking about it.) If you have a dosing cup with only milliliters, the potential for confusion is greatly reduced.

As if that’s not bad enough

Even your actual measuring spoons aren’t as precise as you think they are. At one point I came across information indicating that up to a 20 percent variance is allowed. Again, that 20 percent could cause dosing errors. In researching this article I came across a page called “Cooking for Engineers” with the post:

I’ve got three sets of measuring spoons, and their measurements differ from each other, up to 1/4 teaspoon! Is there a way to know which (if any), are accurate?

The suggestions that followed involved scales and the temperature at which one should measure the water used to determine volume. Too bad no one suggested going metric.

Additional endorsement of the metric system for health reasons

I also have a document from the Institute for Safe Medication Practices (ISMP) called 2014-15 Targeted Medication Safety Best Practices for Hospitals2 . Two of its best practices mention sole use of metric system units.

Best Practice 3: Measure and express patient weights in metric units only.

The rationale:

Significant medication errors have occurred when the patients’ weight is documented in non-metric units of measure (e.g., pounds) and it has been confused with kilograms (or grams). Numerous mistakes have been reported when practitioners convert weights from one measurement system to another, or weigh a patient in pounds but accidently document the value as kilograms in the medical record, resulting in more than a two-fold error.

Best Practice 5: Purchase oral liquid dosing devices (oral syringes/cups/droppers) that only display the metric scale.

ISMP has received more than 50 reports of mix-ups between milliliter (mL) and household measures such as drops and teaspoonfuls, some leading to injuries requiring hospitalization.

Beware teaspoon and tablespoon instructions on prescriptions

Almost uniformly, prescriptions are written in metric units. However, if you pick up a liquid prescription and the dose on the bottle is not metric (and in reads teaspoon and tablespoons), the pharmacy has had to make a conversion. Where there are conversions, there is the potential for mistakes.

In addition, one of the top six recommendations in the 15th annual report of the National Coordinating Council for Medication Error Reporting and Prevention3 includes a “Statement of support for use of the metric system to dose medications.”

Advocate for the metric system and help make the country a healthy place!

Thanks,

Linda

Notes: The article itself requires a subscription http://pediatrics.aappublications.org/content/134/2/e354.full.pdf. However, a summary is located here: http://www.aap.org/en-us/about-the-aap/aap-press-room/Pages/Reducing-Medication-Dosing-Errors-by-Ditching-Teaspoons-and-Tablespoons.aspx.
2 http://www.ismp.org/tools/bestpractices/TMSBP-for-Hospitals.pdf
3  
http://www.nccmerp.org/sites/default/files/fifteen_year_report.pdf