The Physician Ordered an Analgesic Per Orem Every Four Hours

The physician ordered an analgesic per orem every four hours PRN for breakthrough pain for a seventeen-year-old patient who is receiving an epidural narcotic. The nurse should be aware that the best time to administer the analgesic is:

A) When the patient has increased tolerance to the epidural
B) When the patient's mother states that the patient is in pain
C) When the patient states that he is experiencing a sudden increase in pain
D) Every four hours around the clock