PRN (as needed)

How to read it

PRN is written in capitals or as p.r.n. The American Heritage Dictionary gives the Latin as pro re nata, “as the situation demands; as needed”, and MedlinePlus, the US National Library of Medicine’s health site, lists PRN as “as needed”, an abbreviation a doctor may write on a prescription. PRN is not on the Joint Commission’s “Do Not Use” list or ISMP’s list of error-prone abbreviations. ISMP’s 2019 guidelines for electronic prescribing single it out in another way: prescribing systems are to require the purpose of every PRN (as needed) medicine to be entered with the order.

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PRN nurses

On a job advert or a staff rota, PRN describes a nurse who works as needed. The American Nurses Association glosses pro re nata as “as the need arises”, and sets PRN nurses apart from per diem nurses: a per diem nurse can work for several facilities and is not bound by one facility’s minimum hours, but does not get the workplace benefits a PRN nurse does.

PRN in British hospitals

NHS services use PRN in the same sense. The Lincolnshire Partnership NHS Foundation Trust’s list of jargon for carers gives “as and when required medication”, and Rowcroft Hospice’s guide for new prescribers gives “when required”. The Minnesota Board of Pharmacy’s list of prescription abbreviations has an older Latin shorthand with a similar sense, s.o.s. (si opus sit, “if there is a need”). Where a medicine is wanted at once rather than when needed, the shorthand is STAT.