Yet another drug calculation question

[MPKH, BSN, RN]

I am studying for my drug calculation quiz, and I came across this question that I need your help on...I think I may be making it more difficult than it actually is.

The question is: Ampicillin Suspension 200 mg po q6h. How many mLs of water will the nurse add to reconstitute this medication? The label that came with the question states that the drug comes in a 100 ml bottle and that there is 125 mg of the drug in 5 ml of the suspension after reconstituted. The dispensing direction on the label states that you make the suspension by adding 85 ml of water to the mixture, and doing that will yield 100 ml suspension with 125 mg ampicillin contained in each 5 ml of the suspension.

Is the answer simply 85 ml? Or is there some calculation involved...I am thrown off by the 200 mg part.

Thanks =)

[hypocaffeinemia, BSN, RN]

You're correct. The 200mg is the dose, not the concentration.

If it says to add 85mL of water to reconstitute the bottle, do it.

You'd then have a bottle with 125mg / 5mL concentration and would have to give 8 mL of the product to make each dose.