How do you calculate a drug dose when the medication is supplied as a concentration in mg per mL and the order is in mg?

How do you calculate a drug dose when the medication is supplied as a concentration in mg per mL and the order is in mg?

• A. Volume (mL) = Dose (mg) ÷ Concentration (mg/mL) × 2
• B. Volume (mL) = Dose (mg) × Concentration (mg/mL)
• C. Volume (mL) = Dose (mg) ÷ Concentration (mg/mL)
• D. Volume (mL) = Dose (mg) ÷ Concentration (mg/mL) × 0.5

Answer: (C)

When the dose is given in mg and the medication’s strength is in mg per mL, you determine the volume to administer by dividing the dose by the concentration. This works because concentration tells you how many milligrams are in each milliliter, so dividing the total milligrams you need by the number of milligrams per milliliter tells you how many milliliters to administer. For example, if the order is 250 mg and the solution is 50 mg/mL, the volume to give is 250 ÷ 50 = 5 mL. The units cancel to leave milliliters, which is the amount you administer. Always keep units consistent and, after calculating, verify with a second check and use the appropriate syringe markings for the calculated volume. Multiplying by factors or using wrong operations would not yield a correct volume and can lead to incorrect dosing.

When the dose is given in mg and the medication’s strength is in mg per mL, you determine the volume to administer by dividing the dose by the concentration. This works because concentration tells you how many milligrams are in each milliliter, so dividing the total milligrams you need by the number of milligrams per milliliter tells you how many milliliters to administer.

For example, if the order is 250 mg and the solution is 50 mg/mL, the volume to give is 250 ÷ 50 = 5 mL. The units cancel to leave milliliters, which is the amount you administer.

Always keep units consistent and, after calculating, verify with a second check and use the appropriate syringe markings for the calculated volume. Multiplying by factors or using wrong operations would not yield a correct volume and can lead to incorrect dosing.