HELP with PCA Dosage Calc -- cannot find samples to follow...

[chamrob]

I think I posted in wrong area first time... sorry!!

Hi -- I have been struggling since Friday to study for Dosage Calc in the AM and find probs matching the sample we were given. We are using the Pickar 8th Editon, only PCA reference is on page 369. The online site practice questions contained nothing and have been working them from Chapter 15 - 17. My instructor just said she does not know the answer to the sample and I am lost on it.... This is exactly what she gave us to study :

Patient weighs XXX kg

Begin on XXX med PCA 10 mg/mL

Rate of 8 mg (she put 8 in parenthesis) q 15 min with lockout of 24 mg/hr

Bag has 150 mL

Started at 0800, if patient receives 3 doses/hr how long will bag last?

I have worked it:

150mL / 10mg/mL = 15 mg/mL

8 mg / 15 mg = 0.533 = 0.5 mg/mL q 15 min x 3doses/hr =

You see -- I am confusing myself horribly .... I usually make 100% on these Dosage Calc Quizzes -- I need every point I can get --

Thanks in advance for your help - I am truely stumped and frustrated -- and too tired ... thinking I am over thinking it....