p.r.n.

Abbreviation meaning "when necessary" (from the Latin "pro re nata", for an occasion that has arisen, as circumstances require, as needed). One of a number of hallowed abbreviations of Latin terms that have traditionally been used in prescriptions. Some others: {{}}a.c. = before meals (from "ante cibum", before meals) b.i.d. = twice a day (from "bis in die", twice a day) gtt. = drops (from "guttae", drops) p.c. = after meals (from "post cibum", after meals) p.o. = by mouth, orally (from "per os", by mouth) q.d. = once a day (from "quaque die", once a day) q.i.d. = four times a day (from "quater in die", 4 times a day) q._h.: If a medicine is to be taken every so-many hours (from "quaque", every and the "h" indicating the number of hours) q.h. = every hour q.2h. = every 2 hours q.3h. = every 3 hours q.4h. = every 4 hours t.i.d. = three times a day (from "ter in die", 3 times a day) ut dict. = as directed (from "ut dictum", as directed)

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Abbreviation for L. pro re nata, as the occasion arises; when necessary.

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as needed [Lat. pro re nata]

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[L.] pro re naґta (according to circumstances).