Pro re nata

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Pro re nata is a Latin phrase meaning in the circumstances or as the circumstance arises.[1] It is commonly used in medicine to mean as needed or as the situation arises. It is generally abbreviated to p.r.n. in reference to dosage of prescribed medication that is not scheduled; instead, the decision of when to administer the drug is left to the nurse, caregiver or the patient's prerogative.[2] Such administration of medication is not meant to imply, and should never allow for, exceeding a given daily dosage.

Other uses[edit]

Pro re nata is sometimes used for blood tests. A physician will write a p.r.n. order for blood work. The patient may then use that order when needed.

The initials p.r.n. may also refer to casual, or "as needed", employment.


  1. ^ Oxford Latin Dictionary s.v. nascor ~ī nātus (p. 1156)
  2. ^ Pro re nata does not imply that the patient may take the medicine whenever the patient desires, but rather that the medicine may be taken in the prescribed dosage if needed.

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