The medication order is for 25 mg of diphenhydramine IM for a severe allergic reaction. The vial on hand reads 50 mg/2 mL. How many milliliters should be administered?

The medication order is for 25 mg of diphenhydramine IM for a severe allergic reaction. The vial on hand reads 50 mg/2 mL. How many milliliters should be administered?

• A. 0.5 mL
• B. 2 mL
• C. 0.25 mL
• D. 1 mL

Answer: (D)

Start with the dose-to-volume conversion using the vial’s concentration. The vial has 50 mg in 2 mL, which means the solution contains 25 mg per 1 mL. Since the order is 25 mg, you need 25 mg ÷ 25 mg/mL = 1 mL. Therefore, administer 1 mL IM. This approach ensures the exact dose is given by matching the prescribed mg to the concentration per mL, avoiding underdosing or overdosing.

Start with the dose-to-volume conversion using the vial’s concentration. The vial has 50 mg in 2 mL, which means the solution contains 25 mg per 1 mL. Since the order is 25 mg, you need 25 mg ÷ 25 mg/mL = 1 mL. Therefore, administer 1 mL IM. This approach ensures the exact dose is given by matching the prescribed mg to the concentration per mL, avoiding underdosing or overdosing.