Prescription abbreviations

The abbreviations and their Latin

The Latin and English here are the Minnesota Board of Pharmacy’s, from its list of prescription abbreviations; NPO, Rx and Sig are from the American Heritage Dictionary.

British forms

British prescriptions use other Latin for the same times. The Lincolnshire Partnership NHS Foundation Trust’s list of jargon gives BD for twice a day, TDS for three times and QDS for four times; the Minnesota list gives their Latin, ter die sumendum for t.d.s. and quater die sumendus for q.d.s. Rowcroft Hospice’s guide for new prescribers writes OD, omni die, for every day, and PRN as “when required”. In Britain the same order is written in English: a Norfolk and Norwich University Hospitals leaflet explains “Nil by Mouth” as no food, drink or medications by mouth.

What ISMP and the Joint Commission flag

Two lists mark the abbreviations that lead to mistakes. The Joint Commission created its “Do Not Use” list in 2004. QD and QOD are on it because they are mistaken for each other, the period after the Q read as an I and the O read as an I; the list’s replacements are “daily” and “every other day”. The Pennsylvania Patient Safety Authority reported cases in 2005 of orders written QD that were read as QID, and one written QOD that was given every day.

The Institute for Safe Medication Practices (ISMP) keeps a longer list of error-prone abbreviations. Its 2024 edition flags OD for once daily, which is mistaken for oculus dexter, the right eye, as ISMP Canada’s list does too. It flags BIW and TIW, two and three times a week, which are mistaken for two and three times a day, and per os, whose os is mistaken for OS, the left eye. Its 2015 edition listed BT (bedtime) as mistaken for BID and i/d (one daily) as mistaken for tid, and its 2021 edition lists HS, which can mean half-strength or bedtime. ISMP’s wording for bedtime has changed: its 2015 list gave “nightly” in place of qhs, its 2021 list “nightly or HS”, and its 2024 list flags Qhs and Qn, mistaken for every hour, and gives QHS or qhs for bedtime. ISMP’s 2019 guidelines for electronic prescribing accept BID, TID, QID and HS in capital letters, and PO for clinicians, with “oral” for consumers. Joel Weaver, in Anesthesia Progress in 2006, argued that modern prescribing discourages Latin abbreviations such as b.i.d., t.i.d., h.s., p.c. and a.c. in favour of plain wording.

The same letters elsewhere

On a job advert, PRN describes a nurse who works “as the need arises”, in the American Nurses Association’s words; the ANA sets PRN nurses apart from per diem nurses, who can work for several facilities. STAT is also short for statistic. GTT is also the glucose tolerance test.

Where ℞ comes from

The American Heritage Dictionary and Unicode, which encodes the sign as U+211E PRESCRIPTION TAKE, derive ℞ from recipe, the Latin for “take”, and Woods glosses it as recipe, “take thou”. Other stories are told. History.com, which says most sources give recipe, reports a theory that it comes from the Eye of Horus. Howard Haggard’s Devils, Drugs, and Doctors (1929) calls it an invocation to Jupiter, and Brewer’s Dictionary of Phrase & Fable says its ornamental part is the symbol of Jupiter; Haggard illustrates it with the title page of a Latin version of the medical poem of Salerno, on which every R is crossed.

The parts of a prescription

A 2012 study of handwritten prescriptions in Oman sets out four parts: the superscription, the symbol for recipe; the inscription, with the ingredients, dosage form, strength and route; the subscription, with directions for compounding; and a last part, usually preceded by a sign, with the directions to be written on the dispensed medicine. The Minnesota list glosses sig as “write on label”. Woods describes the final line of a prescription as instructions to the patient, sometimes in English but commonly in abbreviated Latin.