# Confused! Dosage calculations

- 1May 10, '13 by lclopez86I'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?Esme12 likes this. - 2,280 Visits
- 3May 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
- 0May 10, '13 by MadrasHi, 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

- 0May 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? - 0May 10, '13 by
*GrnTea*Quote 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

- 3May 11, '13 by J.A.B.,SNI 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