The healthcare provider prescribes cefazolin 500 mg IM every 6 hours. The available vial is labeled, “Cefazolin 1 gram,”. and the instructions for reconstitution state, “For IM use, add 2.5 mL sterile water for injection to provide a total volume of 3.0 mL.”. After reconstitution, how many mL should be administered to the client? (Enter numeric value only. If rounding is required, round to the nearest tenth.). [No changes needed].
The Correct Answer and Explanation is:
To calculate the correct volume of cefazolin to administer, follow these steps:
- Determine the concentration after reconstitution:
The vial contains 1 gram (1000 mg) of cefazolin, and after adding 2.5 mL of sterile water, the total volume is 3.0 mL.
This gives a concentration of 1000 mg per 3 mL:1000 mg3 mL=333.33 mg/mL\frac{1000 \text{ mg}}{3 \text{ mL}} = 333.33 \text{ mg/mL}3 mL1000 mg=333.33 mg/mL - Calculate the volume required for 500 mg:
You need to administer 500 mg, and the concentration is 333.33 mg/mL. To find the volume (V) to administer, use the formula:V=Desired DoseConcentration=500 mg333.33 mg/mL≈1.5 mLV = \frac{\text{Desired Dose}}{\text{Concentration}} = \frac{500 \text{ mg}}{333.33 \text{ mg/mL}} \approx 1.5 \text{ mL}V=ConcentrationDesired Dose=333.33 mg/mL500 mg≈1.5 mL
Thus, 1.5 mL of the reconstituted solution should be administered.
Explanation:
In this case, cefazolin is supplied as a powder in a vial labeled 1 gram (1000 mg). The instructions for reconstitution direct adding 2.5 mL of sterile water to make a total volume of 3.0 mL. This means the concentration of the drug in the vial after reconstitution is 1000 mg/3 mL, or approximately 333.33 mg/mL.
The healthcare provider has prescribed 500 mg of cefazolin, and to administer this dose, you must calculate how many milliliters contain 500 mg. Using the concentration (333.33 mg/mL), dividing 500 mg by 333.33 mg/mL gives a result of 1.5 mL.
By following this method, you ensure the correct dose is administered safely. It’s important to round to the nearest tenth when required, as medication calculations often involve specific dosing instructions, and small errors can have clinical implications.