If you are refering to chronic lbp and the use of epidurals/nerve root injections, then the mechanism of the pain is the question and not so much the mechanism of the drug. Think about something like RA, people can be consistantly on corticosteroids for extremely long periods of time, works well against the inflammation, but sequele of steroid is hard on the body, but they do their job and decrease inflammation. The case of epidural for LBP is a little more cloudy, usually you are dealing with nerve root inflammation from stenosis of the intervertebral foramen, in that case you are talking about a progressive process in which there is continued narrowing over time resulting in increased compression of the nerve root. Initially steroids may help reduce the nerve root irritation/swelling in early stages of the disease, but eventually they may not alleviate the symptoms. The response of steroids to this kind of process is pretty variable, some patients only need one injection and may be "cured of pain", while others may not have any relief at all, or only minimal relief, and then there are those inbetween who get injections every 4 months or so on a continuing basis. Hope that helps