A solution contains 500 mg of azithromycin reconstituted in 250 mL of 0.9% sodium chloride. What is the concentration in mg/mL?

A solution contains 500 mg of azithromycin reconstituted in 250 mL of 0.9% sodium chloride. What is the concentration in mg/mL?

• A. 2 mg/mL
• B. 0.5 mg/mL
• C. 1 mg/mL
• D. 5 mg/mL

Answer: (A)

Concentration is found by dividing the total amount of drug by the total volume of solution. You have 500 mg of azithromycin in 250 mL, so 500 mg ÷ 250 mL = 2 mg/mL. This means each milliliter of solution contains 2 mg of the drug. The other values would require different volumes (for example, 0.5 mg/mL would need 1000 mL for 500 mg, 1 mg/mL would need 500 mL, and 5 mg/mL would need 100 mL), so 2 mg/mL is the correct concentration.

Concentration is found by dividing the total amount of drug by the total volume of solution. You have 500 mg of azithromycin in 250 mL, so 500 mg ÷ 250 mL = 2 mg/mL. This means each milliliter of solution contains 2 mg of the drug. The other values would require different volumes (for example, 0.5 mg/mL would need 1000 mL for 500 mg, 1 mg/mL would need 500 mL, and 5 mg/mL would need 100 mL), so 2 mg/mL is the correct concentration.