An adult client with maxillofacial surgery pain is prescribed acetaminophen and codeine phosphate oral solution. The solution contains 120 mg acetaminophen and 12 mg codeine per 5 mL, and the dose is 25 mL every 6 hours PRN. How many milligrams of codeine are in one dose?

• A. 60
• B. 30
• C. 12
• D. 24

Answer: (A)

The key idea is to convert the solution’s concentration into the amount in the ordered volume. The codeine concentration is 12 mg per 5 mL. For a 25 mL dose, you’re using five times the 5 mL portion (25 ÷ 5 = 5), so codeine per dose = 12 mg × 5 = 60 mg. Another way is to find mg per mL: 12 mg ÷ 5 mL = 2.4 mg/mL, then 2.4 mg/mL × 25 mL = 60 mg. One dose contains 60 mg of codeine.