PTCB Sig Codes Study Guide: Abbreviations, Roman Numerals, and Days Supply

The codes you should be able to translate cold

Start with route and frequency, because those two pieces drive both the label and the math. “po” is by mouth. “sl” is sublingual. “pr” is rectal. “au,” “ad,” and “as” refer to both ears, the right ear, and the left ear. “ou,” “od,” and “os” refer to both eyes, the right eye, and the left eye. Ear and eye pairs are classic mix-ups, which is why many pharmacies spell “right eye” and “left ear” in full. “gtt” means drop. “ac” is before meals and “pc” is after meals. “hs” is at bedtime. “prn” is as needed. “stat” is immediately. [1]

Frequency codes: “qd” or “daily” is once a day, “bid” is twice, “tid” is three times, and “qid” is four times. “q4h” means every four hours, which is not the same as “qid.” Every four hours can be six doses in a day. Four times daily is often four doses during waking hours. That difference changes a days supply. “qod” means every other day. “qwk” is weekly. If a sig includes “prn,” do not invent a daily maximum that is not written. If the question says “up to four tablets daily,” use that maximum when it asks for days supply at maximum use.

Roman numerals still appear on some prescriptions and in older teaching sets. I is 1, V is 5, X is 10, L is 50, and C is 100. Add when numerals descend from left to right: XVI is 16. Subtract when a smaller numeral comes first: XIV is 14, IX is 9, XL is 40. “ss” is sometimes used for one-half. None of this replaces reading the whole sig. A numeral next to the wrong unit is still the wrong dose.

Error-prone abbreviations are part of the exam

The Institute for Safe Medication Practices maintains a list of abbreviations, symbols, and dose designations that have been misread. “U” for units can look like a zero or a four. “IU” can look like IV. “QD” and “QOD” can be confused with each other or with “QID.” Trailing zeros and naked decimal points change doses by a factor of ten. The PTCE patient-safety domain specifically mentions leading and trailing zeros and limiting error-prone abbreviations. Order-entry questions and safety questions are allowed to test the same idea. [4]

So the study task is twofold. Be able to translate a code if a question asks what it means. Be able to choose the safer written form if a question asks which notation prevents a mistake. “Daily” is safer than “QD.” “0.5 mg” is safer than “.5 mg.” “5 mg” is safer than “5.0 mg.” “Units” is safer than “U.” You are not being asked to keep using a dangerous abbreviation just because it is traditional Latin.

When the sig is ambiguous, the workflow answer is not to guess a friendly interpretation. A missing route, a range with no maximum, or an unreadable numeral is a reason to refer the order to the pharmacist, who may need to clarify it with the prescriber. Technicians support that process. They do not invent the missing instruction to keep the queue moving. That role boundary shows up again in the patient-safety guide. Review patient-safety questions next.

Turn a sig into a days supply

Most days-supply items are two steps. First, convert the sig into an amount used per day. Second, divide the amount dispensed by that daily amount. If the sig is “7.5 mL twice daily” and 225 mL is dispensed, daily use is 15 mL and the supply is 15 days. If the sig is “1 tablet tid” and 90 tablets are dispensed, daily use is 3 tablets and the supply is 30 days. Write the units. Milliliters divided by milliliters per day become days. Tablets divided by tablets per day become days. If the units do not cancel, the setup is wrong.

Concentration items add a ratio before the sig math. If a suspension is 250 mg per 5 mL and the dose is 375 mg, the volume of one dose is 375 times 5 divided by 250, which is 7.5 mL. Only then do you apply “twice daily” or “for 7 days.” The separate math article walks five calculation items in full. Use it when the arithmetic, not the abbreviation, is the part you miss. Open the PTCB math practice test.

Maximum-use wording matters. “Take 1 to 2 tablets every 6 hours as needed for pain” does not have one silent days supply. If the question says to use the maximum, calculate the most the directions allow. If it does not, do not assume a number of doses the sig never stated. Insurance days-supply rules in real pharmacies can also differ from a textbook maximum. For the exam, follow the instruction in the stem and say when a real claim would need the pharmacy’s payer rules.

A short practice routine

Day one, make a two-column sheet: code on the left, plain English on the right. Cover one side. Include the ear and eye set and the q4h versus qid pair, because those create the expensive mistakes. Day two, add ten days-supply problems that you write yourself by changing only the volume or the frequency. If you only reread a chart, you will recognize codes and still miss the arithmetic under a timer.

Day three, mix safer-notation questions with translation questions so your brain does not assume every abbreviation on a list is one you should copy onto a label. Then take the five items above and the math set. Log whether the miss was vocabulary, a unit error, or a maximum-use misread. Run another order-entry set once that log has at least one repeated error. The iOS app can keep flashcards if you want the list on your phone. Download RxCertify if that is the routine you will actually use. There is no website account to create.

• Translate route and frequency before you calculate.
• Keep qid and q4h in different rows of your notes.
• Write leading zeros and avoid trailing zeros.
• Refer an ambiguous sig instead of guessing the prescriber’s intent.

Are sig codes still on the PTCE?

The January 2026 order-entry area includes sig codes, abbreviations, medical terminology, and the math used for days supply, quantity, dose, and concentration. Confirm the current outline if you test much later.

Should I use QD on labels because it might be on the exam?

Know what QD is supposed to mean, and know why safety lists reject it. Questions can test either recognition or the safer way to write the frequency.

What is the difference between qid and q4h?

Qid is four times daily. Q4h is every four hours, which can mean six doses in twenty-four hours. The days supply changes with that difference.

How do Roman numerals show subtraction?

When a smaller numeral is written before a larger one, subtract. IX is 9 and XIV is 14. When they descend, add. XVI is 16.

Where are the worked math problems?

Use the PTCB math practice article for full solution steps, then the browser question bank for a new set.