Help with Drug Calculation

[Kastiara, ASN, RN]

I am in my third week of nursing school. We just started drug calculations this week. I'm doing a practice problem in my book that has me stumped. Either the book has a typo or I am missing some concepts. The problem is as follows:

Order: ciprofloxacin 0.1g IV q12h

Available: cipro 200mg/20mL

Set and Solution: secondary IV set with drop factor of 15 gtt/mL; 100 mL D5W

Instruction: dilute ciprofloxacin in 100 mL of D5W and infuse over 60 min

Question one wants to know how many mL per does should be given, which I set up as:

100 mg / 200mg x 20 mL= 10 mL per dose

Question two wants to know the IV flow rate in drops per minute. I set it up like this:

100 mL x 15 gtt/mL / 60 = 25 gtt/min

The book says the answer is 28 gtt/min. I cannot figure out how they got that number. They set the problem up like this:

10mL + 100mL x 15gtt/mL / 60 min = 100 x 15 / 60 = 27.5 or 28 gtt/min

I am so confused right now. Can anyone explain this or show me how I am doing this wrong? Thanks in advance.

[203bravo, MSN, APRN]

what's confusing you? you are adding 10mL of cipro to 100 mL of D5W for a total of 110 mL to be infused over 60 min.

Your formula would be correct if for some reason you withdrew and discarded 10 mL of the D5W prior to injecting the 10 mL of cipro.

[Kastiara, ASN, RN]

Yeah, I wasn't adding the 10mL of cipro into the calculation.

Thanks.