The order is for Zithromax 500 mg PO. The supply on hand is Zithromax oral suspension 200 mg/5 mL. How many milliliters should be given?

The order is for Zithromax 500 mg PO. The supply on hand is Zithromax oral suspension 200 mg/5 mL. How many milliliters should be given?

• A. 12.5 mL
• B. 5 mL
• C. 25 mL
• D. 50 mL

Answer: (A)

Dosing a liquid medicine uses its concentration to convert milligrams to milliliters. The suspension is 200 mg in 5 mL, which is 40 mg per 1 mL. To deliver 500 mg, multiply by the volume per mg: 500 mg ÷ 40 mg/mL = 12.5 mL. You can also see it as 500 mg × (5 mL / 200 mg) = 12.5 mL. Check: at 40 mg/mL, 12.5 mL gives 12.5 × 40 = 500 mg. If you gave 5 mL, you’d give 200 mg; 25 mL would be 1000 mg, and 50 mL would be 2000 mg. So 12.5 mL is the correct amount.

Dosing a liquid medicine uses its concentration to convert milligrams to milliliters. The suspension is 200 mg in 5 mL, which is 40 mg per 1 mL.

To deliver 500 mg, multiply by the volume per mg: 500 mg ÷ 40 mg/mL = 12.5 mL. You can also see it as 500 mg × (5 mL / 200 mg) = 12.5 mL.

Check: at 40 mg/mL, 12.5 mL gives 12.5 × 40 = 500 mg. If you gave 5 mL, you’d give 200 mg; 25 mL would be 1000 mg, and 50 mL would be 2000 mg. So 12.5 mL is the correct amount.