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About this tool
Decode BD, TDS, HS, PRN and other prescription shorthand, work out doses per day and total quantity, and spot unsafe abbreviations.
Prescription shorthand is abbreviated Latin: BD is bis in die (twice a day), TDS is ter die sumendum (three times a day), HS is hora somni (at bedtime) and PRN is pro re nata (as needed). This decoder translates a whole sig line, works out doses per day, the gap between doses, the course length written as 5/7 or 3/12, and the total number of tablets that adds up to — and it flags shorthand that appears on the ISMP list of error-prone abbreviations.
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Paste your code or data sample into the workspace.
Pick the format, conversion, or analysis you need.
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Frequency, timing, route, form and duration are pulled out of one paste, not looked up one at a time.
Doses per day multiplied by course length gives the quantity to dispense, so a short-supply is obvious.
Abbreviations on the ISMP error-prone list, trailing zeros and naked decimals are highlighted with the reason.
BD means twice a day (bis in die), TDS means three times a day (ter die sumendum) and QDS means four times a day (quater die sumendum). The American equivalents are BID, TID and QID. Roughly, twice a day is every 12 hours, three times a day every 8 hours and four times a day every 6 hours, unless the label says otherwise.
It is the course length written as a fraction with the time unit on the bottom: 5/7 is five days, 2/52 is two weeks and 3/12 is three months. This convention is common in UK and Indian prescribing. Combined with the frequency it gives the quantity — 1 tablet TDS for 5/7 is 15 tablets.
PRN is pro re nata, meaning take only when needed, and a safe PRN instruction always carries a maximum in 24 hours and a reason such as “for pain”. STAT is statim, meaning give one dose immediately. SOS (si opus sit) sits between them and means one dose if necessary.
The ISMP list of error-prone abbreviations includes U for unit (read as 0 or 4, turning 4U into 40), IU for international unit (read as IV), QD and QOD (confused with QID), µg for microgram (read as mg, a 1000-fold error), cc for millilitre, trailing zeros such as 1.0 mg and naked decimals such as .5 mg. If any of these appear on something you have been given, ask the pharmacist to confirm the dose before taking it.