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definitions

p.r.n.

  1. (in prescriptions) as the occasion arises; as needed.

Origin of p.r.n.

From the Latin word prō rē nāta
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for prn

prn

abbreviation for (in prescriptions)
  1. pro re nata

Word Origin for prn

Latin: as the situation demands; whenever needed
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
prn in Medicine

p.r.n.

abbr.
  1. pro re nata (as the situation demands)
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.