A head laceration in a patient with an MVA requires acetaminophen 650 mg every 4 hours. The pharmacy provides 500 mg/5 mL. How many milliliters per dose should be given?

• A. 5.0 mL
• B. 6.5 mL
• C. 8.0 mL
• D. 9.0 mL

Answer: (B)

Converting the prescribed dose into the amount to administer uses the drug’s concentration. Here, 500 mg in 5 mL means 100 mg per each milliliter. To give 650 mg, you need 650 ÷ 100 = 6.5 mL. So the dose per administration should be 6.5 mL. The other volumes would deliver different milligram amounts (for example, 5 mL would be 500 mg, 8 mL would be 800 mg, etc.), which is why 6.5 mL is the correct amount. If needed, verify with a calibrated syringe to measure exactly 6.5 mL.