A healthcare provider prescribes cefazolin 350 mg intramuscularly (IM) every 8 hours for a… — NCLEX-PN

A healthcare provider prescribes cefazolin $350$ mg intramuscularly (IM) every $8$ hours for a client with a respiratory infection. The medication is supplied in a vial containing $500$ mg of cefazolin powder. The reconstitution instructions on the label state: 'Add $2.0$ mL of sterile water for injection to provide a total reconstituted volume of $2.2$ mL.' How many milliliters (mL) should the practical nurse (PN) withdraw to administer one dose? Record your answer to the nearest tenth. Do not include units in your answer.

Answer: 1.5 mL

Answer

1.5

To calculate the correct volume for a reconstituted medication, the nurse must use the total volume yielded after the powder is dissolved, not just the volume of the diluent added. The formula is

\frac{\text{Desired}}{\text{Have}} \times \text{Volume} = \frac{350}{500} \times 2.2 = 1.54

mL. Rounded to the nearest tenth, the correct amount to administer is

1.5

mL.

Step-by-Step Solution

Identify the prescribed desired dose.

350

This is the target amount of medication required for a single administration.

Determine the final concentration of the medication on hand.

500

mg in

2.2

When reconstituting a powder, the total resulting volume (

2.2

mL), not the diluent volume (

2.0

mL), must be used to calculate concentration because the powder adds displacement volume.

Apply the dosage calculation formula:

\frac{\text{Desired}}{\text{Have}} \times \text{Volume}

\frac{350}{500} \times 2.2

This mathematical relationship ensures the correct proportion of liquid is drawn to deliver the exact milligram amount requested.

Calculate the exact volume and round to the nearest tenth.

1.54

mL rounds to

1.5

Rounding instructions require one decimal place for standard clinical precision.

Key Concept

Reconstituted Medication Dosage Calculation

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