Can anyone clarify IBW vs ABW vs Adj BW for CrCl on NAPLEX?

[john888]

Which should be used on the NAPLEX if they don't clarify in the question?

My RxPrep book says to go by BMI: actual BW if underweight (BMI<18.5), IBW if normal (18.5-24.9), and adjusted BW if overweight (>/= 25)

But on the SDN 120 calc questions, #118, the patient's BMI=27 and IBW is used (while RxPrep would advise adjusted BW be used)

I called NABP to ask about this and they said they aren't allowed to answer the question specifically but that the exam questions would be clear about what to use. However, I've read multiple posts on SDN where people say their CrCl questions didn't say which weight to use.

From what I've read, some people say to just use IBW unless otherwise specified?

Any help is appreciated - it would be a shame to lose points for something arbitrary like this. Thanks!

---

Members don't see this ad.

 

[myska]

If the problem specifies which to use, follow the directions. Otherwise, this is what I understood from RxPrep/school:
Actual < IBW : use actual
Actual > IBW, but less than 130% of IBW : use IBW
Actual > IBW, AND more than 130% of IBW : use adjusted

Does this line up with what other people use?

 

[Carbon14]

I agree with myska. Read the exam questions carefully. When the exam doesn't specify which calculation they want you to go by, use myskas explanation. For example, if I ask you to dose a medication based on the patients weight, its your job to determine whether they're underweight, within 130% of IBW, or exceed 130% of IBW. I can make the question tricky by providing answer choices that include "correct" drug doses for all 3 situations. Don't make the mistake of automatically assuming that the patient is within 130% of IBW. Also, don't overanalyze the situation. If the patient exceeds 130%, it will be blatantly obvious after you work the math out. The patient won't be 129.5% or 130.4%....think more along the lines of 135 and up.

 

[PharmD_Rx2014]

I took the exam today and it DID specify which weight to use. If not, I would agree to use the rules stated above, but I only had one CrCl question.

 

[john888]

Thanks for the replies everybody - I will go with myska's advice. Two weeks to go until the exam!

PharmD_Rx2014 thanks for chiming in and congrats on taking the exam - what did you think of it?
Surprised you only got one CrCl question - sounds like the test can vary a huge amount with regards to how many questions of each type people receive

On a similar note - do the same rules apply for weight-based dosing (if they don't specify which weight to use)?

 

[Pharmguy171]

This is a great question. I had a multiple choice CrCl question on a patient who was over 130% of IBW. The question did not clarify which weight to use but after calculating it out with both methods, both answers were choices :/

 

[kamac]

How about the rounding up or rounding down. Do we need to do it at every step (in case of multiple multiplications or divisions) or else only for the final numerical answer?
Would appreciate response from those who have taken the test.

 

[kamac]

Bump

 

[john888]

I would imagine we only round the final answer.

Of course, depending how long the numbers are at each step, you may need to round to some degree during the problem just so you can write down/re-enter the numbers in the calculator, but I would retain as many digits as possible until the final answer