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Hong KongSig codes
Sig codes encode route, frequency and timing. The exam tests the ones that resemble each other, so learning them in contrasting pairs beats learning a list.
Pure recall, and worth securing early because every days-supply question depends on it.
Frequency
| Code | Means | Doses a day |
|---|---|---|
| QD or daily | Once a day | 1 |
| BID | Twice a day | 2 |
| TID | Three times a day | 3 |
| QID | Four times a day | 4 |
| Q4H | Every four hours | 6 |
| Q6H | Every six hours | 4 |
| Q8H | Every eight hours | 3 |
| Q12H | Every twelve hours | 2 |
| PRN | As needed | Variable |
An as-needed instruction has no fixed daily quantity, so days supply cannot be calculated from the Sig alone. Where a question involves PRN it will give you a maximum daily use, and that maximum is what you calculate with.
Route
| Code | Means |
|---|---|
| PO | By mouth |
| SL | Sublingual |
| PR | Rectally |
| IV | Intravenous |
| IM | Intramuscular |
| SC or SubQ | Subcutaneous |
| OD, OS, OU | Right eye, left eye, both eyes |
| AD, AS, AU | Right ear, left ear, both ears |
The pairs that catch people
The eye and ear codes are the classic. O is for eye and A is for ear, D is right and S is left, U is both. Getting the letter families the wrong way round is a recognized error type, which is why the plain-English forms are now preferred in practice.
Q6H and QID both mean four a day but they are not interchangeable in scheduling, and the exam sometimes cares about the difference.
Quantity and timing
- AC before meals, PC after meals
- HS at bedtime
- STAT immediately
- gtt drop, tsp teaspoon, tbsp tablespoon
- ss one half
How to learn them
In contrasting pairs rather than alphabetically. AC against PC, OD against AD, Q6H against QID. The exam tests the confusion, so practice the confusion.
Common questions
What does BID mean?
Twice a day. TID is three times and QID is four.
How many doses is Q4H?
Six a day.
What do OD and AD mean?
OD is right eye and AD is right ear. O is eye, A is ear, D is right, S is left, U is both.
Why is PRN a problem for days supply?
It has no fixed daily quantity, so the question must supply a maximum daily use.
How should I learn Sig codes?
In contrasting pairs, because the exam tests the ones that look alike.