Confused! Dosage calculations

1 I'm having difficulties completing this problem.
Ordered: Retrovir 200 mg/kg/Day IV q4 hr in 60 mL LR over 90 mins.
On Hand: Retrovir 3 g vials. Each gram is reconstituted with 4 mL of diluent
patient weighs 182 lb. Use macrotubing 20 gtt/mL
Dilute the reconstituted Retrovir in 48 mL of LR
calculate flow rate:
I know the formula is:
I'm having troubles differentiating what is "filler" and what is not.
So far I have:
 Convert lbs to Kg
182 lbs (1 kg/2.2 lbs) = 182/ 2.2= 82.73 kg
 Find ordered dose in mg/day
200mg/kg/day
(200mg/kg/day) X 82.73 kg = 16,545.45 mg/day
 Find ordered dose in mg/dose
Q4hrs therefore give 6 doses in one day
(16,545.45 mg/day) X (6 doses/1 day) = 99272. 73 mg/dose
 Find concentration of medication on hand:
3 g is 3000 mg
Each gram is reconstituted in 4 mL
3000 mg/12 mL = 250 mg/mL
From here I'm completely lost, am I even in the right directions? What further steps do I need to take to solve or understand this problem? 

May 10, '13 by nursebride2012All you need to do is multiply 60 by 20 is 1200 and divide by 90 and your answer is 13.333333 rounded is 13gtt/min


May 10, '13 by Esme12, ASN, BSN, RN Senior Moderatornice job on a long problem..... however....you ordered dose daily:
This patient weighs 82.73kg x 200mg/kg/day= 16546mg/day.
Order is for q4h: that's 6 doses. 16546mg/6 doses= 2757mg per dose...so recalculateLast edit by Esme12 on May 10, '13 
May 10, '13 by Madras, ASN, RNHi, I'm just a student myself so anyone correct me if I'm wrong....
To get the ordered dose daily:
Pt weighs 82.73kg x 200mg/kg/day= 16546mg/day.
Order is for q4h: that's 6 doses. 16546mg/6 doses= 2757mg per dose.
You have Retrovir 3000mg/12ml equivalent to 250mg/ml
2757mg/ 250mg= 11.028ml is what would be added into the 48ml of LR so approx 60mL of LR to be infused over 90 minutes.
So you've got 60ml/90 minutes= 0.6666666667 x20gtts/min= 13.33 round to 13gtts/min

May 10, '13 by AmberHopefulRNQ4hrs therefore give 6 doses in one day
(16,545.45 mg/day) X (6 doses/1 day) = 99272. 73 mg/dose
The way I am reading it here, you would be giving 595,636.38 mg per day to the patient. Or am I missing something? 
May 10, '13 by lclopez86you're right, instead of dividing, I multiplied. thank you for catching my error!

May 10, '13 by nurseprnRNQuote from lclopez86So one dose is 2757mg. Now you should be able to figure how many reconstituted cc of the med will go in the minibag to make a total of 60cc, and then you can figure out how fast to run it.I'm having difficulties completing this problem.
Ordered: Retrovir 200 mg/kg/Day IV q4 hr in 60 mL LR over 90 mins.
On Hand: Retrovir 3 g vials. Each gram is reconstituted with 4 mL of diluent
patient weighs 182 lb. Use macrotubing 20 gtt/mL
Dilute the reconstituted Retrovir in 48 mL of LR
calculate flow rate:
I know the formula is:
I'm having troubles differentiating what is "filler" and what is not.
So far I have:
 Convert lbs to Kg
182 lbs (1 kg/2.2 lbs) = 182/ 2.2= 82.73 kg
 Find ordered dose in mg/day
200mg/kg/day
(200mg/kg/day) X 82.73 kg = 16,545.45 mg/day
You're perfect to here. Good thinking.
 Find ordered dose in mg/dose
Q4hrs therefore give 6 doses in one day
(16,545.45 mg/day) X (6 doses/1 day) = 99272. 73 mg/dose
Um, no. That's a dose for the whole day, so for six doses you'd divide that by six. Look at what you have. You've determined that you're going to give 16,545.45 mg/day...so why would ONE dose be a whole lot bigger than that?
 Find concentration of medication on hand:
3 g is 3000 mg
Each gram is reconstituted in 4 mL
3000 mg/12 mL = 250 mg/mL


May 11, '13 by EaglesWings21, ASNI would try to look up how to do dimensional analysis. It really helped me with dosage calculation and I got a 100% on my test this past semester. This website has a powerpoint that shows you how to do it:
Dosage Calculation Using Dimensional Ana 
