A client is ordered intravenous magnesium sulfate at 3 g/hr. The medication label shows 20 g of magnesium sulfate in 1000 mL of normal saline. How many mL per hour should be infused?

A client is ordered intravenous magnesium sulfate at 3 g/hr. The medication label shows 20 g of magnesium sulfate in 1000 mL of normal saline. How many mL per hour should be infused?

• A. 100 mL/hr
• B. 150 mL/hr
• C. 50 mL/hr
• D. 75 mL/hr

Answer: (B)

Converting a dose rate to an IV flow rate using the solution’s concentration is the key idea. If the bag has 20 g in 1000 mL, the concentration is 20 g/1000 mL or 0.02 g per mL. To deliver 3 g each hour, multiply by the volume corresponding to that amount: 3 g × (1000 mL / 20 g) = 150 mL per hour. So the infusion should run at 150 mL/hr. This approach uses dimensional analysis to keep units consistent and ensures the ordered dose per hour is met accurately.

Converting a dose rate to an IV flow rate using the solution’s concentration is the key idea. If the bag has 20 g in 1000 mL, the concentration is 20 g/1000 mL or 0.02 g per mL. To deliver 3 g each hour, multiply by the volume corresponding to that amount: 3 g × (1000 mL / 20 g) = 150 mL per hour. So the infusion should run at 150 mL/hr. This approach uses dimensional analysis to keep units consistent and ensures the ordered dose per hour is met accurately.