To calculate how many mL of diluted vancomycin should be added to a 250 mL bag, let's break this into logical steps:

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Step 1: Understand the prescription

• Mrs. Smith's dose: 1250 mg (twice daily).
• Concentration of vancomycin infusion solution: ≤ 5 mg/mL.
• Each 500 mg vial is reconstituted with 10 mL water for injection, creating a concentration of 50 mg/mL.

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Step 2: Determine the volume needed for 1250 mg

The prescribed dose is 1250 mg, so calculate the volume required to administer this dose at the 5 mg/mL concentration:

$\text{Volume (mL)} = \frac{\text{Dose (mg)}}{\text{Concentration (mg/mL)}} = \frac{1250}{5} = 250 \, \text{mL}.$

This means 250 mL of the final diluted solution will contain the required 1250 mg of vancomycin.

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Step 3: How much of the concentrated solution (50 mg/mL) to use?

We need to calculate the volume of the reconstituted concentrated solution (50 mg/mL) to prepare 250 mL of diluted solution at 5 mg/mL.

1. The total vancomycin dose required is 1250 mg.
2. Using the concentrated solution (50 mg/mL):

$\text{Volume of concentrated solution (mL)} = \frac{\text{Dose (mg)}}{\text{Concentration (mg/mL)}} = \frac{1250}{50} = 25 \, \text{mL}.$

So, 25 mL of the reconstituted concentrated solution (50 mg/mL) is needed.

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Step 4: Add 25 mL of the concentrated solution to the 250 mL bag

To ensure a final concentration of 5 mg/mL, you dilute the 25 mL of 50 mg/mL concentrated solution in the 250 mL bag.

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Final Answer

You should add 25 mL of the reconstituted vancomycin concentrate to the 250 mL infusion bag.

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Questions to consider:

1. What would you do if the concentration of the final infusion solution was limited to 4 mg/mL instead of 5 mg/mL?
2. How would the volume change if the patient’s weight required a lower dose of vancomycin?
3. What is the purpose of diluting vancomycin to this specific concentration (e.g., 5 mg/mL)?
4. How do you ensure accurate measurement when reconstituting and transferring vancomycin?
5. What precautions should you take when administering vancomycin via infusion?

Tip:

Always double-check calculations when preparing medications, especially high-risk drugs like vancomycin, to avoid underdosing or overdosing.