A nurse is providing discharge teaching to the parent of a child who is prescribed diphenhydramine 25 mg elixir every 4 hr as needed

A nurse is providing discharge teaching to the parent of a child who is prescribed diphenhydramine 25 mg elixir every 4 hr as needed. The amount available is diphenhydramine elixir 12.5 mg/5 mL. How many mL should the nurse administer per dose? (Round the answer to the nearest tenth. Use a leading zero if it applies. Do not use a trailing zero.)

The Correct Answer and Explanation is:

To determine how many milliliters (mL) of diphenhydramine elixir should be administered per dose, you can use the following steps to perform a unit conversion calculation.

Problem:

You need to administer 25 mg of diphenhydramine, but the available elixir concentration is 12.5 mg/5 mL.

Solution:

1. Identify the required dose and the concentration of the elixir:
   • Required dose: 25 mg
   • Concentration: 12.5 mg per 5 mL
2. Calculate the amount of elixir needed to provide the required dose.To determine how many mL of the elixir will provide 25 mg of diphenhydramine, you use the following formula:Volume required=(Desired doseConcentration)×Volume of elixir available\text{Volume required} = \left(\frac{\text{Desired dose}}{\text{Concentration}}\right) \times \text{Volume of elixir available}Volume required=(ConcentrationDesired dose​)×Volume of elixir availableSubstitute the values into the formula:Volume required=(25 mg12.5 mg)×5 mL\text{Volume required} = \left(\frac{25 \text{ mg}}{12.5 \text{ mg}}\right) \times 5 \text{ mL}Volume required=(12.5 mg25 mg​)×5 mLSimplify the calculation:Volume required=2×5 mL=10 mL\text{Volume required} = 2 \times 5 \text{ mL} = 10 \text{ mL}Volume required=2×5 mL=10 mLSo, the nurse should administer 10 mL of the diphenhydramine elixir per dose.

Explanation:

1. Conversion from mg to mL:
   • The concentration of the elixir tells us that 12.5 mg is present in every 5 mL of the elixir. To find out how much volume is needed for 25 mg, we use the ratio of 25 mg to 12.5 mg.
2. Setting up the ratio:
   • Since 12.5 mg corresponds to 5 mL, 25 mg is twice that amount (25 mg / 12.5 mg = 2). Therefore, the volume required will also be twice that of 5 mL, which equals 10 mL.
3. Rounding:
   • Since the calculation results in a whole number (10 mL), rounding is not necessary. However, you should always check the final unit measurement and ensure it matches the prescribed amount.

Thus, administering 10 mL of the diphenhydramine elixir will deliver the required 25 mg dose.