The large surface area of the stomach and small intestines provide a huge area for absorption. The oral route, of course, is cheap, low-tech, and almost always available. Most patients can benefit from oral opioids, and the therapeutic index is broad enough for most of them to allow this simpler and more reliable route for therapy. The key to making oral therapy successful, and thereby avoiding invasive therapies such as epidural or intraspinal drug delivery, is assiduous attention to management of side effects. Most patients who start opioids experience transient sedation.
Proactive management is key to successful therapy.
The patient should be told to expect sedation, and to expect it to be transient. They should be reminded that a person in pain sleeps poorly, and that when the pain is relieved they will feel drowsy as they get caught up on lost sleep. After a few days, they should expect their wakefulness to improve. This will allow them to be wakeful at doses of opioids necessary to maintain good pain control. Forewarning the patient of this possibility will reduce the likelihood of the patient's rejecting the therapy on the basis of a side effect that will ultimately prove to be transient.