Sig Code Interpretation: PTCB Practice Guide

Reading Prescription Sig Codes Like a Pro

Interpreting sig codes (from the Latin "signa," meaning "write on the label") is a fundamental pharmacy technician skill tested on the PTCB certification exam. Sig codes are the shorthand instructions that tell the patient how to take their medication. Being able to translate these codes quickly and accurately is essential for daily practice and exam success.

Worked Example 1

Sig: i tab PO BID AC

Translation: Take one tablet by mouth twice daily before meals.

Breakdown:

• i = one (Roman numeral)
• tab = tablet
• PO = by mouth (per os)
• BID = twice daily
• AC = before meals (ante cibum)

Worked Example 2

Sig: ii gtt OS Q4H PRN pain

Translation: Instill two drops in the left eye every 4 hours as needed for pain.

Breakdown:

• ii = two
• gtt = drops (guttae)
• OS = left eye (oculus sinister)
• Q4H = every 4 hours
• PRN = as needed

Worked Example 3

Sig: iss tsp PO QHS x 10 days

Translation: Take one and a half teaspoons by mouth at bedtime for 10 days.

Breakdown:

• iss = one and a half (i = 1, ss = one half)
• tsp = teaspoon (5 mL, so 1.5 tsp = 7.5 mL)
• PO = by mouth
• QHS = every bedtime (quaque hora somni)
• x 10 days = for 10 days

Worked Example 4

Sig: Apply thin layer TOP to affected area TID

Translation: Apply a thin layer topically to the affected area three times daily.

Breakdown:

• TOP = topically
• TID = three times daily

Worked Example 5

Sig: i cap PO QD c food

Translation: Take one capsule by mouth once daily with food.

Breakdown:

• i = one
• cap = capsule
• PO = by mouth
• QD = once daily
• c = with (cum)

Worked Example 6

Sig: ii puffs INH Q4-6H PRN SOB

Translation: Inhale two puffs every 4 to 6 hours as needed for shortness of breath.

Breakdown:

• ii = two
• puffs = inhalation doses
• INH = by inhalation
• Q4-6H = every 4 to 6 hours
• PRN = as needed
• SOB = shortness of breath

Common Sig Code Pitfalls

• QD vs QID: QD is once daily; QID is four times daily. Confusing these is a common error, which is why ISMP recommends writing "daily" instead of QD.
• OD vs OS vs OU: OD is right eye, OS is left eye, OU is both eyes. These are easily confused.
• AD vs AS vs AU: AD is right ear, AS is left ear, AU is both ears.
• AC vs PC: AC is before meals, PC is after meals. Both affect how the medication works.

Practice Interpreting Sigs

The more sig codes you practice interpreting, the faster and more accurate you will become on the PTCB exam. Challenge yourself with prescription interpretation questions at PTCBprep mini exams and review abbreviations with our flashcard system. Build your complete study plan at PTCBprep.