Question

Order: Magnesium sulfate 5 gm in 100 ml of D₅W infused over 3 hours. Drug available: Magnesium 500 mg/ml. How many mls of Magnesium would you add to the 100ml of D₅W?

Your tubing drip factor is 10gtts/ml. How many gtts/min will you infuse?

The physician prescribes codeine gr 1/2 po every 3 hr prn for pain. Available on the unit is codeine 30 mg per tablet. How many tablets would you administer?

Answer 1

1) How many mls of Magnesium would you add to the 100 ml of D₅W?

• The order indicates that you need 5 gm of Magnesium. However you have only a magensium solution of 500 mg/mL. Then, we need to calculate what volume of this solution will contain 5 gm of Magnesium. Using conversion factors, we get:

2) How many gtts/min will you infuse?

• The time to infuse the solution is 3 hours, first we transform the time from hours to minutes

• during this time we will infuse 110 mL of solution (100 mL of D5W + 10 mL of Mg 500 mg/mL). Then, we can calculate the rate in mL/min:

• As the tubing drip factor is 10 gtts/mL, then, we can transform the drip rate from mL/min to gtts/min:

3) How many tablets would you administer?

• You need to administer 0.5 gr of codeine every 3 hr and the codeine available is 30 mg / tablet.
• We calculate how many tablets of codeine 30 mg are needed to obtain the desired dose of 0.5 gr:

• To adiminister 0.5 gr of codeine you need 17 tablet of codeine 30 mg/tablet