The route of administration is how a drug gets into your body and travels to the area it is meant to target.
There are numerous routes of administration – from the familiar oral route, to injections into the epidural space or muscle or surgically implanted drug pumps, just to name a few. Why so many? Can’t taking a pill help?
The effectiveness of a drug taken by mouth has to do with, among other things, what happens as it travels through the gastrointestinal system. All oral medication must be digested and absorbed before the active ingredient is released into your body.
Deterrents to a problem-free experience with oral medication might include side effects or be related to dosage, i.e. how much medicine you need in order to get the pain relief you seek.
It's possible that digestive enzymes could destroy the drug before it has a chance to have an effect. And some drugs have a hard time being absorbed from the small intestine into the area of body where they are supposed to do their work. Timing is another factor. When a drug goes through your gastrointestinal system, the chemistry that affects absorption is not always understood. Therefore, your doctor may not know how or if the pill will help you reduce pain. Absorption affects when the drug works, and the lack of understanding about it is a reason enteric-coated medications were developed.
Another reason there is more than one possible route of administration is that some people cannot eat, and so cannot take a pill. This is usually because of the patient’s condition or the presence of a disease.
Brunton, L., Parker, K., Blumenthal, D., Buxton, I. Goodman & Gilman’s Manual of Pharmacology and Therapeutics. McGraw-Hill 2008 New York
Jain, K., MD. Drug Delivery Systems, Humana Press. 2008, Totowa, NJ.