What is another term for "as needed" in medical contexts?

In medical contexts, "as needed" is commonly referred to as "PRN," which is an abbreviation derived from the Latin phrase "pro re nata." This term is used to describe medications or treatments that are to be administered only when necessary, rather than on a scheduled basis. For example, a physician might prescribe pain medication PRN, indicating that the patient should take it only when they are experiencing discomfort rather than at set intervals throughout the day.

The other options, while they may convey a sense of flexibility, do not specifically capture the medical guideline or standard implied by "as needed." "Whenever" suggests a less formal approach without the same specification of need, "AN" is not a recognized abbreviation in this context, and "optional" implies a choice that could lead to misunderstanding in a medical setting, where specific instructions about necessity are crucial for effective care.