Lessons · Nursing · desired over have, times quantity
Desired over have, times quantity
The dose to give is what the order wants, divided by what one tablet or one measured volume holds, times that volume: D / H × Q. The units on D and H must be the same so they cancel.
Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.
What it is for
This is the one formula on the track. The order says 500 mg, the label says 250 mg per tablet, and the 0600 pass has eleven of these in it. A nurse who says the formula in words every time does not put the have on top, and putting the have on top is the mistake that gives half a dose or double.
How to think about it
Write three lines: what is ordered (D), what you have and what it comes in (H per Q), then D / H × Q. Check the units of D and H match; convert first if they do not. Say the answer in words: I want 500, each holds 250, so I need two.
Worked example
Ordered 500 mg. Have 250 mg per tablet.D is 500 mg. H is 250 mg. Q is one tablet.
Tablets = 500 / 250 × 1 = 2 tabletsDesired over have, times the quantity it comes in. Two tablets.
Ordered 250 mg. Have 125 mg per 5 mL.The same formula with a liquid. Q is now 5 mL, the volume the label's strength is in.
mL = 250 / 125 × 5 = 10 mLTwo lots of 5 mL. Ten millilitres.
Your turn
Ordered 400 mg; the label says 100 mg per 5 mL. Write the line.
mL = 400 / × 5 = 20 mL
Solve one, graded on the server
The trap
Putting the have on top. 250 / 500 × 1 = 0.5 tablet, and it looks like a plausible dose. Say it in words: I want 500 and each tablet holds 250, so the answer has to be more than one.