Dosage Calculations

Editorial Team / Admin · Aug 23, 2017

It's looking right to me except for the next to last *, unless there's something I"m missing? Have you been told you have an incorrect answer?

KelRN215, BSN, RN · Aug 23, 2017

I thought I had dosage calculations down now I am on my second to last med surg class and the dosage calculations are so confusing! I have went on dosage help. com and I just don't see any examples of these questions. I know how to do some of the question and then I just get lost......this is driving me NUTS! I mean, it is supposed to be simple math. This is the scenario and what I have thus far....
Order: Administer ceftazidime(Fortaz) 250mg twice daily IVPB
The label on the drug guide reads, reconstitute with 10ml of sterile water. Compatible with normal saline and lactated ringers. Dilute in 100 ml of IV solution. Infuse over 30 minutes. The patient is also receiving vancomycin 500 mg IVPB every 12 hours.
*What is the total volume of the infusion? (I am saying) 110ml or 220ml for 24 hrs.?
*What type of IV solution are you going to use to administer the medication? (ME) Normal saline or Lactated ringers
*What rate should the nurse set the IV pump? (ME)Volume/Time= 110/0.5=220ml/hr
*Program IV pump for infusion of ceftazidime. (ME) 220ml/hr/250mgx110=8.8ml/hr
*How many mg will the patient receive? 250mg twice daily =500 mg
I realize I am probably totally wrong if anyone can help or steer me in the right direction I would really appreciate it!

You calculated the rate at 220 mL/hr then in the next step programmed the pump to run at 8.8 mL/hr. Why? The 250 mg (which is a ridiculously low dose of ceftaz) is irrelevant when programming the pump. If you run a 110 mL bag at 8.8 mL/hr, you are administering every dose over 12.5 hrs. You wouldn't even get both doses in in 24 hours at that rate. I can't really figure out your thinking on this one to guide you. Enlighten me.

Trauma Columnist · Aug 23, 2017

Moved to Nursing student assistance

Chronicallychanging · Aug 25, 2017

I don't understand my own thinking!!!! So I guess I should stop with calculations at question #4 and program the pump for 220ml/hr. Is that right ? I seems I often take things further than needed and end up getting the question wrong. These questions were given to us by an instructor.

bgxyrnf, MSN, RN · Aug 26, 2017

Order: Administer ceftazidime(Fortaz) 250mg twice daily IVPB
Reconstitute with 10ml of sterile water. Dilute in 100 ml of IV solution. Infuse over 30 minutes. The patient is also receiving vancomycin 500 mg IVPB every 12 hours.
*What is the total volume of the infusion? Sure, 110 mL...10 from the reconstitution and 100 from the dilution.
*What type of IV solution are you going to use to administer the medication? Normal saline because (a) it's cheaper than LR and (b) it's readily stocked in 100mL bags, unlike LR
*What rate should the nurse set the IV pump? Yep, total volume (110 mL) divided by duration of infusion (0.5 hours)
*Program IV pump for infusion of ceftazidime. I don't understand this question. Perhaps it means as you interpreted it... pick "ceftazidime", enter "250 mg in 110 mL over 30 minutes"
*How many mg will the patient receive? Yep, 250 mg per infusion or 500 mg total per day

Your comment, "I realize I am probably totally wrong" reveals a lack of confidence... it really was as simple as it appeared.

bgxyrnf, MSN, RN · Aug 26, 2017

220ml/hr/250mgx110=8.8ml/hr

To follow up on KelRN215's post, I'm likewise confused by what you were intending... and need to point out that your units are inconsistent across the equality.

mL/hr/mg does NOT equate to mL/hr. It appears that you arbitrarily 'canceled' out the unit of weight (that is, 'mg')

Also, the "110" is not a unitless number as you've made it... it is a volume measurement in "mL"

Furthermore, your math equation doesn't hold... 220/250*110=96.8, *not* 8.8

I don't understand the distinction between these two questions:

*What rate should the nurse set the IV pump?
*Program IV pump for infusion of ceftazidime.

KelRN215, BSN, RN · Aug 26, 2017

I don't understand my own thinking!!!! So I guess I should stop with calculations at question #4 and program the pump for 220ml/hr. Is that right ? I seems I often take things further than needed and end up getting the question wrong. These questions were given to us by an instructor.

Yes, if you are trying to administer 110 mL over 1/2 hr, the rate is 220 mL/hr. The dose in mg of the drug is irrelevant. If you have 250 mg in 110 mL, 500 mg in 110 mL, or 1g in 110 mL, the rate would still be 220 mL/hr if you wanted to administer the dose over 1/2 hr.