OTC liquid medicines going metric

Work has been progressing toward standardizing liquid OTC medication labels and accompanying dosing devices like cups and oral syringes so that measurement is carried out using only the metric mL.

by Michael R. Cohen, R.Ph.

Published Mar. 13, 2014, 5:30 a.m. ET

Over-the-counter (OTC) liquid medicines can be found in practically every household. They are commonly used for children or adults who have difficulty swallowing pills. In some cases, the medicine itself is absorbed better and faster in a liquid form, so even people who do not have difficulty swallowing pills might use liquid medicines.

Surprisingly, so far there isn't a standard way for drug manufacturers to state the dosage measure for OTC liquid medicines. Both the directions for use and the markings on a dosing syringe, cup, spoon, or dropper may include one or more of these volume measurements:

Household measurements, such as teaspoons (tsp) or tablespoons (tbsp)
Metric measurements, such as milliliters (mL) or cubic centimeters (cc)
Apothecary measurements, such as drams (dr or ʒ) or ounces (oz or ℥)
Other measurements, such as drops (gtts) or dropperfuls

If these volume measurements are confused with each other, too much or too little of the medicine can be given. Many errors happen where the dosing directions recommend a teaspoonful but the dosing cup that comes with the product is marked not only in teaspoons but also tablespoons, milliliters, drams and ounces and the patient uses an incorrect measure.

Other mistakes have been reported when measuring liquid medicines with household measuring devices like a kitchen teaspoon (tsp) or tablespoon (tbsp). A typical household teaspoon can hold between 3 and 7 milliliters (mL). But the real dose of a teaspoon of medicine is 5 milliliters (mL)—3 mL would not be enough medicine and 7 mL would be too much medicine.

To avoid this confusion, work has been progressing toward standardizing liquid OTC medication labels and accompanying dosing devices like cups and oral syringes so that measurement is carried out using only the metric mL. You're already familiar with mL because it's used as a measure with soda cans and even alcoholic beverages.

There's nothing official yet but it's something that nonprofits like mine have been calling for to reduce medication errors. We've been joined by some industry groups such as the Consumer Healthcare Products Association as well as the CDC, the US Metric Association and others. So far, the FDA has not backed mL as the standard but they do require that companies supply a dosing device that measures liquid volume the same way it's expressed on the label.

The good news is that when I checked liquid OTC products at my local pharmacy the other day I noticed that mL was already the sole volume measurement for several liquid medicines. One example is Delsym cough medicine, labeled and dosed only in mL.

Using just "mL" alone is the best way to eliminate dosing mix-ups. This should also be the standard for prescription liquids. Manufacturers, doctors and pharmacists who choose to continue to prescribe, dispense or sell liquid medicines using any volumetric method other than mL unknowingly increase the risk of a mix-up.