PTCE Sig Codes: Pharmacy Abbreviations and the Do-Not-Use List

Sig codes are the shorthand on almost every prescription. At work I read them all day, and after a while "i tab po q8h prn pain" reads as fast as plain English: take 1 tablet by mouth every 8 hours as needed for pain.

On the PTCE, sig codes show up in two ways. You have to read them to do the math, and you have to know which abbreviations are error-prone and shouldn't be used at all. This post covers both: the codes to know, the Latin that makes them stick, and the do-not-use list.

Where sig codes show up on the PTCE

Two parts of PTCB's content outline (the one in use since January 2026) cover them:

• Order Entry and Processing, 22.5% of the exam, lists "Sig codes (e.g., b.i.d., t.i.d., Roman numerals), abbreviations, medical terminology." PTCB marks it as calculation-based, so expect sig codes inside math problems, not only "what does this mean?" questions.
• Patient Safety and Quality Assurance, 23.75% of the exam, lists limiting error-prone abbreviations as a way to prevent errors.

A question might ask what q.i.d. means. More often, the code is one step in a bigger question. In a days supply problem, you have to know that q6h means 4 times a day before you can even start the math.

Read a sig in order

Most sigs follow the same order, so read them one piece at a time:

i tab po q8h x10d prn pain

i = 1 · tab = tablet · po = by mouth · q8h = every 8 hours · x10d = for 10 days · prn pain = as needed for pain

Put together: Take 1 tablet by mouth every 8 hours for 10 days as needed for pain. The verb (take, instill, apply, inhale) is often left off. You add it based on the form and route.

How often

Most frequency codes are short Latin phrases. Learn what the letters stand for, and you can decode codes you've never seen.

One trap: the q in q.i.d. means four (quater), not "every." In q4h, q6h and q.a.m., the q means every (quaque).

Every-so-many-hours codes are where the math hides. Divide 24 by the hours to get doses a day:

q12h and b.i.d. both mean 2 doses a day, but q12h sets the timing: one dose every 12 hours. That matters for drugs that need steady levels, like some antibiotics.

When and how long

A common combination: a.c. and h.s. means before each meal and at bedtime. That's 3 + 1 = 4 doses a day.

Routes

Eyes and ears

The trick: O is for eye (oculus, like "ocular") and A is for ear (auris, like "audio"). D is right (dexter, like "dexterity"), S is left, and U is both.

These six are on the PTCE, but they're also on ISMP's error-prone list, because the eye and ear codes get mixed up with each other. That's why the safer practice is to write "right eye," "left ear" and so on.

Amounts and symbols

PTCB's outline names Roman numerals specifically, so know the basics: i = 1, v = 5, x = 10. A prescription for "#xxx" means 30, and "iv" is 4. On prescriptions they're often written in lowercase.

Fun fact: gtt comes from gutta, Latin for "drop." That's where Gutta gets its name.

Four sigs worked the way the exam asks

1. ii tabs po bid x5d. How many tablets?

• Take 2 tablets by mouth twice daily for 5 days.
• 2 tablets × 2 times a day × 5 days = 20 tablets

2. 1 gtt OU qid. Quantity: 10 mL. What's the days supply?

• Instill 1 drop in both eyes 4 times a day.
• 10 mL × 20 drops per mL = 200 drops
• 1 drop × 2 eyes × 4 times = 8 drops a day
• 200 ÷ 8 = 25 days

3. i tab po q4-6h prn pain. Quantity: 30. What's the days supply?

• Take 1 tablet by mouth every 4 to 6 hours as needed for pain.
• For a range or "as needed," use the most the patient could take: every 4 hours is 6 tablets a day.
• 30 ÷ 6 = 5 days

4. i cap po ac and hs. Quantity: 120. What's the days supply?

• Take 1 capsule by mouth before meals and at bedtime.
• 3 meals + bedtime = 4 capsules a day
• 120 ÷ 4 = 30 days

For more practice with this kind of math, see PTCE math: every formula you need.

The abbreviations you shouldn't use

This is the Patient Safety side. The exam can ask what an abbreviation means and why it's dangerous, so learn both.

The Joint Commission's official "Do Not Use" list. Organizations accredited by The Joint Commission, like most hospitals, must not use these:

The decimal rules are easy to remember as a pair: always a zero before the decimal point, never a zero after it when the dose is a whole number.

ISMP's longer list. The Institute for Safe Medication Practices keeps a bigger list of error-prone abbreviations. These are the ones most likely to come up:

A note on SUBQ: ISMP's 2024 list recommends writing SUBQ (all capitals, no spaces or periods) or "subcutaneously." Older references often say "subcut."

How to make them stick

• Learn the Latin pieces first. Once you know that b, t and q (quater) mean 2, 3 and 4, and that i.d. means "in a day," the frequency codes decode themselves.
• Translate both ways. Turn shorthand into plain English, then turn plain English back into shorthand. The exam can go either direction.
• Do the math with them. Practice turning every code into doses a day, since that's how most questions use them.
• Learn the do-not-use list as pairs. For each one, know the mix-up it causes: QD looks like QID, U looks like 0, OD can mean right eye or once daily.

The short version

• Sig codes are in Order Entry and Processing (22.5%), usually inside a math question. Error-prone abbreviations are in Patient Safety (23.75%).
• Read a sig in order: amount, form, route, how often, how long, why.
• In q.i.d. the q means four. Everywhere else, q means every.
• Divide 24 by the hours: q4h = 6, q6h = 4, q8h = 3, q12h = 2 doses a day.
• O is eye, A is ear. D is right, S is left, U is both.
• Know the do-not-use list and why each one is dangerous: U, IU, QD, QOD, trailing zeros, missing leading zeros, and MS/MgSO4.

Want to test yourself? Type any sig into the Sig codes tool to see it in plain words, with a warning when it uses an error-prone abbreviation. Then try the free Order Entry practice questions.

Sources: PTCB's PTCE Content Outline (effective January 6, 2026), ISMP's List of Error-Prone Abbreviations, Symbols, and Dose Designations (2024), and The Joint Commission's facts about the "Do Not Use" list. This post is for exam study. At work, follow your pharmacy's procedures and your pharmacist.