Milliequivalence??

Question

I'm a pharmacy student taking the Naplex tomorrow and doing a study guide on math and cannot figure out how the problem is set up. Please help!!

A patient receive 15mls of 10% KCl injection in 1 liter of 0.9% NaCl over 24 hours? Approx how many milliequivalents of Chloride did the patient receive? (K+ = 39, Cl = 35.5, Na = 23)

Answer 1

I guess you've already taken the exam, but someone else may do a search and find this question, so here it is....

The short answer is that for monovalent ions (ions with a single plus or minus charge), one milliequivalent (mEq) is equal to one millimole (mmol).  

(For ions with TWO pluses or minuses, like Ca2+, you need to divide by 2: two milliequivalents is equal to one millimole.)

To get the mmol, you need to divide the weight (g) by the molar mass (g/mol).  Don't forget 1 mol = 1000 mmol.

To get the weight, you need to multiply the concentration (%) by the volume.  Don't forget 1 L = 1000 mL.

So, for example, to calculate the number of milliequivalents for sodium in 1 liter of saline, you first multiply 1000 mL by 0.9% to get 9 g of NaCl.  Since the molar mass of Na is 23, and the molar mass of Cl is 35.5, in 9 g of NaCl you have 0.154 mol, which is 154 mmol.  (154 mmol of Na, and 154 mmol of Cl.)

Or, you can simply look on the bag (of normal saline) or on the net: http://en.wikipedia.org/wiki/Saline_solu...

Obviously, for Cl you'll need to add the Cl in the normal saline  to the Cl in the KCl additive.

Good luck.