For example, apart from being given three to four times a day on a time-contingent basis, ibuprofen or naproxen or most other NSAIDs may be taken p.r.n. (as occasion rises) when pain is troublesome and omitted at other times. 1999, Harold Merskey, Dwight Moulin, “Pharmacological Treatment in Chronic Pain”, in Andrew R. Block, Ephrem Fernandez, Edwin Kremer, editors, Handbook of Pain Syndromes: Biopsychosocial Perspectives, Mahwah, NJ: Lawrence Erlbaum Associates, Inc., →ISBN, page 152: