pro re nata

/ˌproʊˌreɪˈnɑ.tɑ/

From the Latin phrase pro (“for”) rē (“thing, matter”) nātā (“born, arisen”): "for what arises".

1Dealing with something that arises unexpectedly or out of due course; for special business.
2(medicine) Used on medical charts by doctors to indicate that actions may be taken at the discretion of nursing staff depending on the patient's condition.
3(medicine, pharmacology) Used on prescriptions to indicate that the medicines may be taken if and when the patients feel the need.