This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Central Nervous system, Subject name: Pharmacology
In patient-controlled analgesia morphine is given commonly by 
Select and explain. 
A. Intravenous, B. Intramuscular, C. Subcutaneous, D. Sublingual
A: Intravenous
Answer: A: Intravenous 
Explanation: Patient-controlled analgesia (PCA) is now in widespread use for the management of breakthrough pain. With PCA, the patient controls a parenteral usually intravenous infusion device by pressing a button to deliver a preprogrammed dose of the desired opioid analgesic. Has better pain control using less opioid. REF: Katzung 13 TH ED. pg: 554