Lessons · Nursing · a liquid dose in mL
A liquid dose: how much of the bottle
The volume to draw up or pour is the ordered amount divided by the label's strength per millilitre, or D / H × Q with the label's own volume as Q.
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
Liquids are where the errors are biggest, because a syringe will happily hold ten times the dose. The label gives a strength; the order gives an amount; the answer is millilitres, and it is measured in a syringe or a cup with a mark on it.
How to think about it
Write the order. Write the label as mg per mL, converting the units if they differ. Divide the order by the strength per mL, or use D / H × Q with the label's volume. Round as the problem states, and say whether the number fits the syringe you would use.
Worked example
Ordered 40 mg. Label: 80 mg per 2 mL.D is 40 mg. The label's strength is 80 mg in 2 mL.
Per mL: 80 / 2 = 40 mg/mLThe strength per millilitre, so the next line is one division.
mL = 40 / 40 = 1 mLForty over forty. One millilitre.
Ordered 350 mg. Label: 250 mg per 5 mL. mL = 350 / 250 × 5 = 7 mLThe same by D / H × Q with the label's 5 mL as Q. Seven millilitres in an oral syringe.
Your turn
Ordered 60 mg; the label says 20 mg per mL. Write the line.
mL = 60 / = 3 mL
Solve one, graded on the server
The trap
Dividing by the label's volume instead of its strength. 40 mg / 2 mL = 20 and it is not a dose of anything. The order is divided by the milligrams, and the millilitres come back as the unit of the answer.