Dosage Calculations - page 8

by minnielynn

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I am in a desperate situation. I thought I was getting my calculations correctly and today I got back my math results and i got a 70% :crying2: :crying2: :crying2: I am so disappointed I dont know what to do. On my first exam I... Read More

  1. 0
    Quote from aadsmom
    hello, can anyone help me figure out a problem?
    500 mg dopamine in 250ml what rate would equal 5mcg/kg/min. pt wt 106 kg.
    this problem has to be worked by dimensional analysis. there are lots of examples of problems solved by dimensional analysis on this thread for you to also view. you want to end up with the labels of ml/minute with ml in the numerator and minutes in the denominator. this is how this problem is set up and worked:
    5 mcg/1 kg x 1/1 minute (these first two terms are the dose desired) x 106 kg/1 (patient's weight) x 250 ml/500 mg (dose on hand) x 1 mg/1000 mcg (conversion factor) = 0.265 ml/minute. for all practical purposes, however, you would be using an iv pump. most pumps can only be programmed for ml/hour, so this would need to be converted to an hourly rate:
    0.265 ml/1 minute (infusion rate per minute) x 60 minutes/1 hour (conversion factor) = 15.9 ml/1 hour = 16 ml/hour (infusion rate on an iv pump rounded off)
  2. 0
    Quote from Bigbear71
    I am stuck on 2 questions. Still very new to drug calculations. Reading everything I can get my hands on. I'm starting my last semester in an ASN program and we have hardly touched dosage calculations. Basically trying to teach myself. Anyhow, would someone please explain how to do these 2 problems? Thank you very much..

    1. The Dr. has ordered Cordarone IV 900mg to be added to 500 ml D5W and run iv at a rate of 1mg/min for 6 hours. The manufacturer's directions agree with the Dr order. The available 3ml vials of Cordarone contain 50mg per 1 ml. Drop rate is 60 per 1 ml.
    To begin, lets look at what we are asked to infuse TOTAL. So we got 1 mg per minute for 6 hours. Thats 1 (mg) x 60 (minutes) x 6 (hours) or 360 mg. We don't need this now, but it will help us check our math later. Watch...

    How many ml of Cordarone IV should the nurse add to the 500ml D5W?
    There are 3 mls per vial and 50 mg per ml therefore there are 150 mg per vial. For a total of 900 mg to be added, you need to add 18 ml (or 6 vials)

    How many mg of drug are present in 1 ml of the Cordarone IV 900 mg in 500ml D5W?
    Once you add the meds there are 1.7 mg per ml. Here's the math, you have a total of 900 mg in a solution of 518 mls (this is of course after you add the meds, you are adding 18 mls to the 500 ml solution). 900 mg per 518 ml reduces to 1.7 mg per 1 ml.

    How many ml per minute must infuse to deliver the prescribed amount of drug?
    To run at 1 mg per minute, that is 60 mg per hour. If there are 1.7 mg per ml, then you have to figure out how much it will take to get 60 mg in an hour. Take 60 mg / 1.7 mg per ml and you get 35.3 mls per hour. But you are asking about how much per minute, so you have to devide by 60 and you get ~0.6 mls per minute.

    How mant ml per hour should the IV be set to deliver?
    See above. It is 35.3 mls per hour.

    Checking the math:
    35.3 (mls per hour) x 6 (hours) x 1.7 (mg per ml) = 360.06 mg. Looking back at the top, that is was we were asked to infuse. Bingo!

    2. The Dr has ordered Dobutrex 250 mg to be added to 500ml of D5W to run IV at a rate of 5mcg/kg/min. The manufacturer directions agree with the Dr. The available 20 ml vials of Dobutrex contain 250 mg. The IV set delivers 60 drops per 1 ml. The pt. weighs 65kg.
    Start off with a conversion 1000 mcg = 1 mg. So this pt can tolerate 325 mcg per minute. (65 (kg) x 5 (mcg)). Hourly that would be 19,500 mcg (325 mcg x 60 minutes) or 19.5 mg per hour.

    How many ml of Dobutrex should the nurse add to the 500 ml D5W?
    There are 250 mg in a 20 ml vial. The math is done for you. You add 20 mls.

    Based on weight, how many ug/min of Dobutrex should the pt. receive?
    325 mcg per minute (see above)

    How many mg of drug present in ml of the Dobutrex 250mg in 500ml D5W?
    250 mgs in a 520 mls solutin (500 D5W + 20 mls of Dobutrex). 250 mg /520 mls = 0.5 mg per ml.

    How many ml per minute must infuse to deliver prescribed amount?
    Pt can tolerate 325 mcg per minute. That is equivalent to 0.325 mg. There are 0.5 mgs in each ml. 0.325 mg / 0.5 mg per ml is a run rate of 0.65 mls per minute.

    How many ml per hour should the IV set to deliver?
    Going back to the top with the maximum of 19.5 mg per hour and a total of 0.5 mg per ml, the MAXIMUM run rate would be 39 mls per hour. (19.5 / 0.5 = 39)
    Last edit by Salamandrina on Aug 7, '07
  3. 0
    Quote from smurfy
    a pregnant woman is scheduled for labor induction w/pitocin. available is 20 units pitocin in 1000cc lr. the md has ordered the infusion to 3mu/min. how many cc's are ordered per hour?
    first off, you need to know that 20 units of pitocin in 1000cc of lactated ringers gives you 20 mu (milliunits) of pitocin per ml of lactated ringers. you must know this information to get the correct answer to this question. you would find this is a drug reference book. i happened to find it in 2007 intravenous medications, 23rd edition, by betty l. gahart and adrienne r. nazareno on pages 958-960. then, to get the answer in cc/hour:
    3 mu/1 minute (dose desired) x 1 ml/20 mu (dose on hand) x 1 cc/1 ml (conversion factor) x 60 minutes/1 hour (conversion factor) = 9 cc/1 hour (dose to give)
  4. 0
    Quote from lpnlpn
    i am having trouble converting between systems of measurement, i am trying to teach myself the conversion factor method as well as the ratio proportion method but this problem is giving me a bit of a problem the problem is ---3g=gr_____ help!
    this is how i would solve it

    therefore3g = 15 x 3 = 45
    3g = gr45
    i hope this helps you
  5. 0
    gr means grain
  6. 0
    this is how i would solve this problem

    d (desired )/h (have) x q (quantity)
    300,000/200,000 x 5 = 7.5
    round it up to 8
  7. 0
    Free Dosage Calculation Study Ware from Delmar Publishing (interactive - great study tool!):
  8. 0
    Hi can anyone help have an upcoming exam and I'm practicing problems according to my schools study guide that was posted. I've been able to work out all of them except this one even though I think this requires the same formula. The IV is infusing at 20ml/hr and contains 50mg. Nipride in 250ml D5W. The client weighs 185lbs.
    ___kgs. (tenth)
    ___mcg/kg/min to (tenth). I've worked the kgs to 84.1 but can't seem to figure the other half. Thanks in advance for your help..
  9. 1
    Quote from nmb107
    the iv is infusing at 20ml/hr and contains 50mg. nipride in 250ml d5w. the client weighs 185lbs.
    ___kgs. (tenth)
    ___mcg/kg/min to (tenth). i've worked the kgs to 84.1 but can't seem to figure the other half. thanks in advance for your help..
    to convert pounds to killograms:
    185 pounds x 1 kg/2.2 pounds = 84.090909= 84.1 killograms (rounded off to tenths)
    to work the problem by dimensional analysis and using the formula dose desired divided by dose on hand to give you the dose to give:
    dose desired: 20 ml/hour (this already has the patient's weight of 84.1 kg calculated into it)
    dose on hand: 50mg of nipride in 250 ml of d5w
    dose to give: x mcg/kg/minute
    conversion factor: 1 mg = 1000 mcg
    conversion factor: 1 hour = 60 minutes

    plug all figures into the equation and compute. you do not need to figure in the patient's weight since it is already part of the calculation for the dose desired . you must know how to work with fractions and ratios to do this:

    20 ml/1 hour (dose desired) x 50 mg/250 ml (dose on hand) x 1000 mcg/1 mg (conversion factor) x 1 hour/60 minutes (conversion factor) = 66.7 mcg/minute, or 67 mcg/minute, rounded off to a whole number.
    another way to figure this out is to determine how many milligrams of the nipride the patient is getting every hour. that is 4 mg. that figure is determined by taking the 50 mg and dividing it by the total amount in the iv bag (250 mls) to get 0.2 mg/ml. since the infusion is running at 20 ml/hour, you multiply the 0.2 mg/ml times the 20 ml/hour to get that the patient is receiving 4 mg/hour of the nipride. 4 mg converted to mcg is 4,000 mcg/hour (1mg = 1,000 mcg). to figure out how much the patient is getting in one minute, simply divide the 4,000 mcg by 60 (1 hour = 60 minute) and you will still get 66.6666 mcg which you will have to round off to either one decimal or a whole number, whichever your instructor prefers.
    NMB107 likes this.
  10. 0
    Hello everybody,

    This was a question that was gnawing at me since I finished my dosage exam a couple hours ago.

    Available: Tylenol 325mg/tab
    Order: gr X
    How many tablets are you gonna administer?

    Hmmm, is this right:

    325mg : 1 tab :: 600mg : x tab

    325x/325 = 600/325

    x = 1.8 tablets (can you have 1.8 tablets?!)

    -___- that doesn't seem right... Are my grains correct D:?