Sig Codes Quick Reference
Sig codes (from the Latin signa, meaning "write" or "label") are abbreviations used on prescriptions to communicate dosing instructions. Pharmacy technicians must be able to interpret these abbreviations accurately to process prescriptions correctly.
Route of Administration
| Abbreviation | Meaning | Example |
|---|
| PO | By mouth (per os) | Take 1 tab PO daily |
| SL | Sublingual (under the tongue) | Place 1 tab SL PRN chest pain |
| TOP | Topically (on the skin) | Apply TOP to affected area BID |
| INH | By inhalation | INH 2 puffs BID |
| IM | Intramuscular | Inject 1 mL IM once |
| IV | Intravenous | Infuse IV over 30 min |
| SubQ / SC | Subcutaneous | Inject SubQ daily |
| PR | Per rectum | Insert 1 suppository PR Q6H PRN |
| PV | Per vagina | Insert 1 applicatorful PV QHS |
| OU | Both eyes (oculus uterque) | Instill 1 gtt OU BID |
| OD | Right eye (oculus dexter) | Instill 1 gtt OD TID |
| OS | Left eye (oculus sinister) | Instill 1 gtt OS QID |
| AU | Both ears (auris uterque) | Instill 3 gtts AU BID |
| AD | Right ear (auris dextra) | Instill 3 gtts AD TID |
| AS | Left ear (auris sinistra) | Instill 3 gtts AS BID |
| NGT | Nasogastric tube | Administer via NGT |
Frequency
| Abbreviation | Meaning | Example |
|---|
| QD / daily | Once daily | Take 1 tab PO QD |
| BID | Twice daily | Take 1 cap PO BID |
| TID | Three times daily | Take 1 tab PO TID |
| QID | Four times daily | Take 1 tab PO QID |
| Q4H | Every 4 hours | Take 1 tab PO Q4H PRN pain |
| Q6H | Every 6 hours | Take 1 tab PO Q6H |
| Q8H | Every 8 hours | Take 1 cap PO Q8H |
| Q12H | Every 12 hours | Take 1 tab PO Q12H |
| QHS | Every night at bedtime (hora somni) | Take 1 tab PO QHS |
| QAM | Every morning | Take 1 tab PO QAM |
| QPM | Every evening | Take 1 tab PO QPM |
| QOD | Every other day | Take 1 tab PO QOD |
| QWK | Every week | Take 1 tab PO QWK |
| PRN | As needed (pro re nata) | Take 1-2 tabs PO Q4-6H PRN pain |
| STAT | Immediately | Give 1 dose STAT |
| AC | Before meals (ante cibum) | Take 1 tab PO AC |
| PC | After meals (post cibum) | Take 1 tab PO PC |
Dosage Form and Measurement
| Abbreviation | Meaning | Example |
|---|
| tab | Tablet | Take 1 tab PO BID |
| cap | Capsule | Take 2 caps PO TID |
| gtt(s) | Drop(s) | Instill 2 gtts OU BID |
| tsp | Teaspoonful (5 mL) | Take 1 tsp PO BID |
| tbsp | Tablespoonful (15 mL) | Take 1 tbsp PO TID |
| mL | Milliliter | Take 10 mL PO BID |
| mg | Milligram | 500 mg PO TID |
| mcg | Microgram | 100 mcg PO daily |
| g | Gram | Apply 1 g TOP BID |
| supp | Suppository | Insert 1 supp PR Q6H PRN |
| ung / oint | Ointment | Apply ung to affected area BID |
| cr / crm | Cream | Apply crm TOP TID |
| sol / soln | Solution | Instill 2 gtts sol OU BID |
| susp | Suspension | Take 5 mL susp PO BID |
| MDI | Metered-dose inhaler | INH 2 puffs via MDI Q4-6H PRN |
| amp | Ampule | Draw 1 amp for injection |
Other Common Abbreviations
| Abbreviation | Meaning | Example |
|---|
| Rx | Prescription | Rx for amoxicillin 500 mg |
| Sig | Write on label / directions | Sig: Take 1 tab PO BID |
| Disp | Dispense | Disp #30 |
| DAW | Dispense as written | DAW - no substitution |
| NR | No refills | Refills: NR |
| RF | Refill | RF x3 |
| UD / ut dict | As directed | Use UD |
| NKA | No known allergies | Allergies: NKA |
| NKDA | No known drug allergies | Allergies: NKDA |
| AAA | Apply to affected area | Apply crm AAA TID |
| D/C | Discontinue | D/C current medication |
| NPO | Nothing by mouth (nil per os) | Patient is NPO after midnight |
| c (with bar) | With | Take c food |
| s (with bar) | Without | Take s food |
| ss | One-half | Take ss tab PO daily |
| qs | Quantity sufficient | Add water qs to 100 mL |
| ad | Up to | Add diluent ad 500 mL |
| MR | May repeat | Take 1 tab, MR x1 in 4 hours |
| WA | While awake | 1 gtt OS Q2H WA |
ISMP "Do Not Use" List
The Institute for Safe Medication Practices (ISMP) and The Joint Commission maintain lists of abbreviations that should not be used due to confusion risk:
| Do Not Use | Potential Problem | Use Instead |
|---|
| U or u (for "unit") | Mistaken for 0, 4, or cc | Write "unit" |
| IU (International Unit) | Mistaken for IV or 10 | Write "international unit" |
| Q.D. / QD | Mistaken for Q.I.D. | Write "daily" |
| Q.O.D. | Mistaken for Q.D. | Write "every other day" |
| Trailing zero (1.0 mg) | Mistaken for 10 mg | Write "1 mg" |
| Lack of leading zero (.5 mg) | Mistaken for 5 mg | Write "0.5 mg" |
| MS, MSO4, MgSO4 | Confused with each other | Write "morphine sulfate" or "magnesium sulfate" |
Exam Tips
- Practice translating full sig lines: "i tab PO BID ac" means "Take one tablet by mouth twice daily before meals."
- Know the ISMP "Do Not Use" abbreviation list - it is commonly tested.
- Remember that QD means once daily, QOD means every other day, QID means four times daily - these are easily confused.
- Be able to calculate days supply from a sig code (e.g., #30 tabs, 1 tab PO BID = 15-day supply).