A nurse is reviewing the medication list of a client. Which of the following medication instructions should the nurse identify as being prescribed using a metric unit?

A. Take 0.5 oz 30 minutes before meals and at bedtime: The unit "oz" (ounce) is not a metric unit. Ounces are part of the imperial measurement system, not the metric system. The metric equivalent of ounces for liquid measurements would be milliliters (mL). Therefore, this prescription is using an imperial unit. B. Take 1 tsp four times daily: The unit "tsp" stands for teaspoon, which, although used in common medical practice, is not a metric unit. A teaspoon is a unit of volume in the U.S. customary system, equivalent to approximately 5 mL in the metric system. However, teaspoons themselves are not part of the metric system, so this instruction is not using a metric unit. C. Take 2 drops four times daily: The unit "drops" is a non-metric unit of measurement and is used to describe small volumes of liquid, often in medication dosages. While the exact volume of a drop can vary depending on the liquid and dropper, it is not a metric measurement. D. Take 15 mL, 1 hr after meals and at bedtime: The unit "mL" stands for milliliters, which is a metric unit of volume. The prescription specifically uses the metric system for dosage measurement, making it the correct option. Milliliters are the standard unit for measuring liquid medications in the metric system.