What is the listed concentration for phenylephrine solution?

• A. 4 mg/100 ml
• B. 40 mg/250 ml
• C. 20 mg/500 ml
• D. 100 mg/250 ml

Answer: (B)

The key idea is understanding concentration as amount per volume so you can dose IV meds accurately. Read each option as mg per mL (or convert to mcg/mL) to compare:

• 4 mg in 100 mL = 0.04 mg/mL (40 mcg/mL)

• 40 mg in 250 mL = 0.16 mg/mL (160 mcg/mL)

• 20 mg in 500 mL = 0.04 mg/mL (40 mcg/mL)

• 100 mg in 250 mL = 0.40 mg/mL (400 mcg/mL)

The commonly used working concentration for phenylephrine infusions in many practice materials is 160 mcg/mL (40 mg in 250 mL), which matches the second option. This concentration lets you reach typical dosing rates (in mcg per minute) with practical infusion flow rates. The other options produce concentrations that are either too low or too high for convenient, safe dosing, making them less practical for standard use.