Confused! Dosage calculations

  1. 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:


    1. Convert lbs to Kg

    182 lbs (1 kg/2.2 lbs) = 182/ 2.2= 82.73 kg


    1. Find ordered dose in mg/day

    200mg/kg/day
    (200mg/kg/day) X 82.73 kg = 16,545.45 mg/day


    1. 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


    1. 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.
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  3. 11 Comments so far...

  4. 3
    All 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
    loriangel14, Esme12, and lclopez86 like this.
  5. 1
    thank you for your help
    Esme12 likes this.
  6. 3
    nice 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 recalculate
    Last edit by Esme12 on May 10, '13
    GerberaDaisy, KelRN215, and lclopez86 like this.
  7. 0
    Hi, 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

  8. 0
    Q4hrs therefore give 6 doses in one day
    (16,545.45 mg/day) X (6 doses/1 day) = 99272. 73 mg/dose
    Shouldn't this be (16,545.45 mg/day) / (6 doses/1 day) = 2757.58 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?
  9. 0
    you're right, instead of dividing, I multiplied. thank you for catching my error!
  10. 0
    Quote from lclopez86
    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:


    1. Convert lbs to Kg

    182 lbs (1 kg/2.2 lbs) = 182/ 2.2= 82.73 kg


    1. 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.


    1. 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?

    1. 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
    So 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.
  11. 0
    Ok I get it now too! LOL
  12. 3
    I 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
    RN2Be77, lrbersamina, and Tinker88 like this.


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