If cefazolin dose is reduced to 400 mg using the same concentration (1 gram per 3 mL), what volume should be administered?

• A. 1.2 mL
• B. 1.5 mL
• C. 2.0 mL
• D. 2.5 mL

Answer: (A)

When the concentration is fixed, the volume you administer scales directly with the dose. Here, 1 gram corresponds to 3 milliliters. A 0.4 gram (400 mg) dose is 40% of 1 gram, so the required volume is 0.4 × 3 mL = 1.2 mL. Another way: the concentration is 1000 mg per 3 mL, which is about 333 mg/mL. 400 mg ÷ 333 mg/mL ≈ 1.2 mL. Therefore, administer 1.2 mL.