Math Question Help

[Eithanhunt]

Can't solve this for the life of me. Assistance required please ?

Order: Hycamtin (topotecan HCl) 1.5 mg/m2 IV daily for 5 days, repeat every 21 days.

The label on the vial reads 4 mg and the manufacturer's directions states "Reconstitute each vial with 4 mL of sterile water. Withdraw the dose and further dilute in 50 mL D5W and infuse over 90 minutes." Calculate the rate of flow in milliliters per hour for a client who weighs 92 kg and is 183 cm tall.

A. 29.6 mL/h
B. 87.5 mL/h
C. 114 mL/h
D. 100 mL/h

[Rose_Queen, BSN, MSN, RN]

Ok, let's start with the dose. What information do you need to determine your dose? It is orders in milligrams per square meters. What would you use to find the number of square meters? Then you will have what you need to calculate the dose you need to give your patient.

Next, you need to look at the drug you have on hand. In order to give the ordered dose, how much do you need to give?

Once you've done that, what do you think your next step would be?

[Eithanhunt]

The BSA is 2.16, meaning the dose is 3.24mg

On hand is 4mg/4mL

So...Desired/Have on hand * Quantity would be 3.24mg/4mg * 4mL = 3.24mL

Here is where I get stuck. I add 3.24 mL to the 50mL D5W to get a total volume of 53.24mL to infuse over 90 min. So 53.24mL/90 min * 60 min/1 hr = 35.49 mL/hr. But that's not the answer, so I'm missing something...

[Eithanhunt]

A is the answer, but I'm starting to think Pearson (this is a question from Pearson's online math review) perhaps is incorrect. Please let me know what you get. Thanks!

[Wuzzie]

I’ve worked this problem and I get the same answer you do. Even adjusting for different formulas for BSA and possible errors in the question I could not replicate any of the answers they got. It’s not out of the realm of possibility that there’s is an error on the website. If someone comes along and figures it out don’t feel bad. This isn’t my first rodeo and even I don’t know how they arrived at their answer. BTW, thank you for showing your work without complaint. Some people get very upset that we ask for it but we have a really good reason for asking that only benefits our student members here. You seem to have an excellent grasp on the med math concept. We’re always here to help.

[Eithanhunt]

Thanks for the input Wuzzie. Appreciate it!

[Anonymous865]

What they are doing is diluting 4 mg in 4ml.

Then they are adding the entire 4mg/4ml to the 50 ml D5W.

Then they are figuring out what rate to set the pump so that if you run it for 90 minutes the patient will receive the correct dose. You are only infusing part of the 54 mls.

54ml/4mg x 3.24mg = 43.74 ml.

If you want to infuse 43.74 ml over 90 minutes you set the pump to 29.16 ml/hr.

Of course that is not what the question directed you to do. It directed you to "Withdraw the dose and further dilute in 50 mL D5W"

It looks like this was originally a different problem that they intended to rewrite.

[Wuzzie]

Well geez that's just stupid. Thanks for figuring it out. Perhaps the rewrite was because nobody in their right mind would administer chemo the way they likely originally wrote the question. OP putting more medication than ordered in an IVPB and relying on the pump to stop infusing prior to overdosing is not great practice. The pump could fail or one of your helpful co-workers might notice that the fluid didn't completely infuse and run the rest in for you. For some medications (antibiotics for instance) the overage probably wouldn't matter but with certain medications the results could be disastrous.