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Sig code decoder

Q: What does PRN mean in pharmacy?

PRN stands for pro re nata, Latin for as needed or as the situation demands. It means the medication should be taken when required rather than on a fixed schedule. For example, 1 tablet PRN pain means take 1 tablet when needed for pain.

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Translate prescription sig codes and Latin pharmacy abbreviations into plain English. Search any abbreviation, QD, BID, TID, PRN, AC, PC and 200+ more. ISMP error-prone abbreviations are flagged.

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Complete sig code reference

Prescription sig codes: Latin roots and why errors happen

Prescription sig codes are abbreviated Latin instructions, a legacy of the era when Latin was the universal language of medicine. Most practitioners today don't speak Latin, which means sig codes are learned by rote and misread through pattern-matching rather than understanding.

The ISMP error-prone abbreviations list

The Institute for Safe Medication Practices (ISMP) publishes a list of abbreviations that have caused medication errors. QD (once daily) looks like QID (four times daily) in poor handwriting, a 4-fold dose error. U (units) has been misread as 0, causing 10-fold insulin errors. MS can mean morphine sulfate or magnesium sulfate. These abbreviations are flagged in this tool and should never be used on handwritten prescriptions.

DAW codes

DAW (Dispense As Written) codes are used in pharmacy billing to indicate whether the prescriber requires brand dispensing or permits generic substitution. DAW 0 means the prescriber permits generic. DAW 1 means the prescriber requires brand. DAW 2 means the patient requests brand. DAW codes 3-9 cover other specific scenarios. Once you've decoded the sig, use our Days Supply Calculator to calculate quantity and billing, and the NDC Lookup to verify the correct product code.

Frequently asked questions

What does QD mean on a prescription?

QD stands for quaque die, Latin for once daily. However, QD is on the ISMP error-prone abbreviations list because it can be misread as QID (four times daily) in poor handwriting. The preferred alternative is to write "daily" or "once daily" in full.

What does PRN mean in pharmacy?

PRN stands for pro re nata, Latin for as needed. It means the medication should be taken when required rather than on a fixed schedule. For example, 1 tablet PRN pain means take 1 tablet when needed for pain.

What is the difference between AC and PC in pharmacy?

AC stands for ante cibum, meaning before meals. PC stands for post cibum, meaning after meals. These instructions affect how the drug is absorbed and tolerated. Metformin is taken PC to reduce GI side effects. Some antibiotics and levothyroxine are taken AC to optimise absorption.