Glossary
BID
BID means twice a day, from the Latin bis in die. It is two doses in a day rather than a strict every-12-hours schedule — the fixed-interval order is written Q12H.
BID means twice a day. The letters are all that is left of bis in die, Latin for "twice in a day", and the pattern runs through the family: TID (ter in die) three times, QID (quater in die) four times, QD (quaque die) once.
BID is a frequency, not a stopwatch. A twice-a-day order is two doses in the waking day, and the prescriber may deliberately put them at morning and evening; when the interval itself matters — antibiotics, some anticonvulsants, drugs whose blood level has to stay steady — the order is written Q12H, and that one is a fixed 12-hour clock. The distinction is tested, and it is the reason a technician does not silently convert one into the other. The arithmetic can come out the same: for 30 days at one tablet per dose, BID and Q12H are both 60 tablets. Only the schedule differs, and only the patient knows which one they were told.
Two practical points. The label prints the expansion — Take 1 tablet by mouth twice a day — because BID is not English. And BID is not itself on the error-prone abbreviation lists: it is QD/QID and HS that those lists replace with words, so a technician who writes out "twice a day" is following the safer habit rather than a rule about BID.
Taught in
Related terms
- TID — TID means three times a day, from the Latin ter in die. It is three doses spread across the waking day, not a strict every-8-hours order — that one is written Q8H.
- QID — QID means four times a day, from the Latin quater in die. It is the abbreviation most often misread as QD, and one tablet four times a day is the classic fourfold-overdose signature.
- QD — QD means once a day, from the Latin quaque die. It is on the Joint Commission's Do-Not-Use List because QD and QID are misread for each other, so the order is written out as "daily".
Source: PTCB — PTCE Content Outline, effective January 6, 2026 (Domain 4 / KA 4.1, "Interpret prescription and medication orders … sig codes, abbreviations, medical terminology and symbols, and days supply", quoted verbatim); The Joint Commission, Official "Do Not Use" List (NPSG.03.05.01 — the minimum list an accredited organization must adopt, read in full); ISMP, List of Error-Prone Abbreviations, Symbols, and Dose Designations (the labels, symbols and abbreviations ISMP asks prescribers to write out) (outline accessed 2026-10-03, verbatim; the Joint Commission and ISMP lists read from their own fact-sheet and recommendation pages 2026-10-06 — each is revised on its own schedule; the definitions here restate this course's own order-interpretation-and-sig guide, which is the page whose sources back every definition above)