Writing doses safely: micrograms and units in full, trailing zeros and naked decimals
Write micrograms (one millionth of a gram) and units in full, put no needless zero after the decimal point, and put a zero in front of a bare decimal point.
Remember
Spell out micrograms (each one millionth of a gram) and units, put a zero before a bare decimal point (0.5 mg) and leave the zero off a whole number (1 mg, not 1.0 mg), because a misread mark can make a dose ten times or a thousand times too large.
Some serious dosing errors start with a dose that is misread rather than miscalculated. Dose errors are the largest single category among prescribing errors, and the most likely to cause serious harm. Each rule closes a gap where one stray mark can turn a safe dose into a harmful one.
A microgram is one thousandth of a milligram, which is itself one thousandth of a gram, and the symbol µg looks very like mg. If µg is read as mg, the patient can receive a dose a thousand times too large, a thousand-fold error. So write micrograms in full. Do the same for units, especially with insulin (a medicine that lowers blood glucose) and heparin (a blood-thinning medicine), because a handwritten U can look like a zero, so 6 U may be read as 60.
Decimals cause similar harm. A trailing zero is a needless zero after the decimal point, as in 1.0 mg. It adds nothing, yet if the decimal point is missed, 1.0 mg can be read as 10 mg, a tenfold overdose (a dose ten times the intended one). Write 1 mg. A naked decimal is a decimal point with no digit in front of it, as in .5 mg, which can be read as 5 mg. Write 0.5 mg instead, with a leading zero (a zero written before the decimal point), so the reader sees a figure first. Avoiding a decimal point is also sound, and a small dose is sometimes written in micrograms to achieve that.
A short rule: lead with a zero, never trail with one.
Key facts
- Micrograms
- write the word in full, because µg can be misread as mg, a thousand-fold error.
- Units
- write "units" in full, because U can be misread as a zero, so 6 U may be read as 60.
- Trailing zero
- write 1 mg, not 1.0 mg, because a missed decimal point can make 1.0 mg read as 10 mg.
- Naked decimal
- write 0.5 mg, not .5 mg, because a missed decimal point turns .5 mg into 5 mg.
- Tenfold and thousand-fold errors
- a U misread as a zero or a missed decimal point can cause a tenfold error, while a µg misread as mg can cause a thousand-fold error.
Exam traps
- A trailing zero does not add clarity, because if the decimal point is missed, 1.0 mg can be read as 10 mg, a tenfold overdose.
- Dropping the zero in front of the decimal is not a harmless saving, because a bare decimal point is easy to overlook, so .5 mg can be read as 5 mg.
- Milligrams can be abbreviated to mg on a drug chart, so the accepted milligram abbreviation is not the problem; micrograms are the unit to write in full.
Read the full notes
Tested in 8 SimpleMed+ questions
Practice it in Pharmacology, with the answer and a full explanation after every question.
Practice these questions