Pro re nata

Pro re nata - Latin literally meaning "For the thing born." but commonly used to mean "as needed" or "as the situation arises."

It is generally used as the acronym PRN in medicine to refer to dosage of prescribed medication that is not scheduled; instead administration is left to the caregiver or patient's prerogative. Most often PRN medications are analgesics such as paracetamol or Vicodin, laxatives such as coloxyl, Sleeping aids such as Ambien, and anti-emetics such as ondansetron.