Final answer:
A client with intractable pain would benefit from a p.r.n. drug regimen because it allows for medication to be administered as needed for unpredictable or sporadic pain relief.
Step-by-step explanation:
Which client would benefit from a p.r.n. (pro re nata, or "as needed") drug regimen? The correct choice is C) One who has intractable pain. P.r.n. medication regimens are designed for administration when a client needs relief from symptoms that are either unpredictable or sporadic. Intractable pain, by definition, is severe, constant pain that is not curable by any known means and which causes a bedridden state if not adequately treated. Therefore, p.r.n. medication would allow for timely intervention when pain episodes occur, maximizing the client's comfort.