United States
Hong KongReading a Sig fast
Candidates rarely misread the abbreviation itself. What they miss is the multiplication of quantity per dose by doses per day. Learn the codes as daily quantities rather than as translations.
Sig codes appear inside other questions rather than as questions of their own, which is why they cost more marks than they look like they should.
Learn them as daily quantities
Not as translations. BID does not mean twice daily; for exam purposes BID means multiply by two.
| Code | Multiply by |
|---|---|
| QD or daily | 1 |
| BID | 2 |
| TID | 3 |
| QID | 4 |
| Q12H | 2 |
| Q8H | 3 |
| Q6H | 4 |
| Q4H | 6 |
Holding them in this form removes a translation step from every days-supply question.
Candidates rarely mistake TID for twice daily. What they do is read "two tablets TID" and use three a day instead of six. Quantity per dose times doses per day is a step that gets skipped whenever the quantity per dose is not one, and the distractor for the skipped version is always among the options.
The hourly forms
Q6H and QID both give four a day. Q4H gives six, which is the one people compute wrong under pressure.
Twenty-four divided by the interval. That is the whole rule and it is faster than recalling a table.
PRN
As needed, so there is no fixed daily quantity and days supply cannot be computed from the Sig alone. A question involving PRN must give you a maximum daily use, and that maximum is what you calculate with.
If you cannot find one, re-read the stem: it is there.
Route and site codes
OD, OS, OU for eyes; AD, AS, AU for ears. O is eye, A is ear, D right, S left, U both.
These are a recognized source of real-world error, which is why plain English is now preferred in practice and why the exam still asks about them.
Ten seconds, not thirty
At about 73 seconds a question, a Sig you have to decode slowly eats a third of the budget before the actual calculation starts. Drill them until the daily quantity arrives with the abbreviation.
Common questions
How should I learn Sig codes?
As daily multipliers rather than translations - BID means multiply by two.
What is the common Sig error?
Forgetting to multiply quantity per dose by doses per day. Two tablets TID is six a day.
How many doses is Q4H?
Six. Divide 24 by the interval.
How do I handle PRN?
It has no fixed daily quantity, so the question must give a maximum daily use.
What do OD and AD mean?
Right eye and right ear. O is eye, A is ear, D right, S left, U both.