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 caretaker or patient's prerogative. Most often PRN medications are oral pain medications such as APAP or Vicodin, antidiarrheals such as Immodium, Sleeping aids such as Ambien, and opioid antagonists such as Naloxone