Pharmacology Math Question

[kaylasmiles4u]

Can anyone help me with understanding how to get the answer to my pharm question? My instructor has given me the answer, but I cannot figure out how to work the problem correctly. Here is the question:

Order reads: D5 1/2NS with 15mEq KCl per liter at 100 mL/hr. On hand is a vial of KCl labeled 20mEq per 10 mL How many mL of KCl should be added to a 500 mL bag of IV fluid?

The answer is 3.75 mL, but I don't know how to get it by working the problem.

Thanks in advance!

[Here.I.Stand, BSN, RN]

My smart aleckey answer is "this problem is stupid, one you will never ever have to calculate" (if you're in the US anyway...not sure how they do it elsewhere. The floors don't even have access to vials of KCl -- only the pharmacy does.)

But anyway, for 15 mEq per liter, you need 7.5 mEq for 0.5L. The vial contains KCl at a concentration of 2 mEq/1mL. 7.5 mEq ÷ 2 mEq/1mL = 3.75 mL

[kaylasmiles4u]

Thank you!