Ten questions on sig codes and the ISMP do-not-use list — the abbreviations you read every shift and the ones you are marked wrong for writing.
Every answer links to the guide it comes from, so if one of these catches you out you can read the whole topic rather than memorise a single fact. The full domain is at Order Entry and Processing.
1. Why does ISMP flag q.d. as error-prone?
Answer: A. q.d. is read as q.i.d. far too often, which turns once-daily dosing into four times a day. Write 'daily' or 'every day'. q.o.d. is separately flagged because it reads as q.d. or q.i.d.; the bedtime/half-strength ambiguity belongs to HS. More: Sig codes, abbreviations and medical terminology
2. A prescription reads 'instil 1 gtt OS bid'. Where does the drop go?
Answer: B. OS is oculus sinister, the left eye. OD is the right eye, OU is both. The ear set runs AD, AS and AU. The pairs that catch people are OS/AS and OD/AD — one letter apart and a different organ. More: Sig codes, abbreviations and medical terminology
3. Which abbreviation should replace 'cc' on a prescription, and why?
Answer: A. ISMP lists cc as error-prone because handwritten cc is mistaken for U, which is itself on the list for being read as 0 or 4. Write mL. The two errors compound: a dose written in cc and misread as units can be off by orders of magnitude. More: Sig codes, abbreviations and medical terminology
4. Why are both SC and SQ flagged as error-prone, and what should be written instead?
Answer: A. SC and SQ are both mistaken for SL, which is sublingual — a completely different route. The safer forms are subcut or subcutaneous written out. This is one of the places where the abbreviation you will actually see in practice is the one you are marked wrong for writing. More: Sig codes, abbreviations and medical terminology
5. A prescription is written '5.0 mg'. What is the risk, and what is the correct form?
Answer: A. A trailing zero is misread as a ten-fold overdose when the decimal point is faint or lost — 5.0 mg becomes 50 mg. The mirror-image rule is the leading zero: never write .5 mg, always 0.5 mg, because a missing leading zero reads as 5 mg. One rule removes a zero, the other adds one, and the exam likes putting them in the same question. More: Sig codes, abbreviations and medical terminology
6. Why is HS on the do-not-use list?
Answer: B. HS is ambiguous: it can mean at bedtime or half strength. Write whichever you mean in full. It sits alongside D/C, which is ambiguous between discharge and discontinue — both are abbreviations whose two meanings lead to opposite actions. More: Sig codes, abbreviations and medical terminology
7. MS and MSO4 are flagged because they are ambiguous between which two drugs?
Answer: A. MS and MSO4 can each mean morphine sulfate or magnesium sulfate, and MgSO4 is separately confused with MSO4. Spell both out. These are drugs with entirely different indications and risks, which is why the ambiguity is on the list rather than merely untidy. More: Sig codes, abbreviations and medical terminology
8. 'Take 1 capsule TID for 10 days.' How many capsules are dispensed?
Answer: C. TID is three times daily. 1 capsule × 3 doses × 10 days = 30 capsules. The trap is QID, which is four times daily and would give 40 — and q.d. misread as q.i.d. is exactly how that error happens in practice. More: Sig codes, abbreviations and medical terminology
9. One tablespoon equals how many millilitres?
Answer: C. 1 tbsp = 15 mL = 3 tsp, and 1 tsp = 5 mL. The next one up is the fluid ounce at 30 mL (29.6 mL exactly), which is two tablespoons. These three conversions carry most of the household-measure questions on the exam. More: Sig codes, abbreviations and medical terminology
10. What does 'qs' or 'QSAD' direct you to do?
Answer: B. qs is quantum satis — a sufficient quantity — and QSAD is 'add a sufficient quantity to make'. It appears in compounding directions, where the final volume is specified rather than the amount of vehicle added. 'As directed' is UD, which is a different instruction entirely. More: Sig codes, abbreviations and medical terminology
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