Certified Medical Assistant (CMA AAMA)PharmacologyMedium
A physician prescribes cefazolin 500 mg IV every 8 hours. The pharmacy supplies cefazolin 1 gram powder for reconstitution. The instructions state to reconstitute with 5 mL of sterile water to yield 200 mg/mL. How many milliliters should the medical assistant administer per dose?
- A1.5 mL
- B2.5 mL
- C3.0 mL
- D2.0 mL
Show answer & explanationAnswer & explanation
Correct answer: B. 2.5 mL
To calculate the correct dosage, use the formula: (Desired Dose / Available Concentration) = Volume to Administer. Desired dose is 500 mg. Available concentration is 200 mg/mL. So, 500 mg / 200 mg/mL = 2.5 mL.
Why the other options are wrong
- A. Incorrect calculation based on wrong concentration or desired dose.
- C. Incorrect calculation; this would be 600 mg.
- D. Incorrect calculation; this would be 400 mg.
Dosage Calculation (mg/mL)
To determine the volume of medication to administer when the order is in milligrams and the concentration is in milligrams per milliliter, divide the desired dose by the available concentration.
- Formula: Desired / Have = Volume.
- Ensure units match (mg to mg).
- Ignore reconstitution volume if concentration is already given.
Memory trick: Don't Hesitate, Calculate!