Amgen and Pfizer sell etanercept under the name Enbrel to treat rheumatoid arthritis but it is also prescribed for a number of 'off-label' conditions, including back pain. The drug works by blocking a molecule called TNF that promotes inflammation.
A team of researchers led by Johns Hopkins University anesthesiologist Steven P. Cohen compared etanercept to steroids and placebos in a clinical trial of 84 adults with sciatica, a condition commonly caused by a herniated disc pressing on the sciatic nerve that starts in the lower spine and runs down the backs of both legs.
The scientists published their results on Monday in the journal Annals of Internal Medicine.
Researchers hypothesized that TNF blockers would be better than steroids at preventing pain since the blockers prevent TNF from binding to receptors in the central nervous system - thereby getting at the root cause of sciatica, Cohen said in a phone interview.
Etanercept seemed like an enticing alternative to epidural steroid injections, which can provide only temporary relief and, in rare instances, cause paralysis or death.
But the Hopkins-led study found that in the short term, patients on steroids reported less pain and less loss of function than the patients given etanercept or a saline placebo.
On a pain scale of 0 to 10, with 10 denoting the worst pain, the average score for the group before treatment started was 6.2. Patients who received steroids reported an average pain score of 2.1 after one month, compared with an average of 3.6 reported by the etanercept group and an average of 3.8 in the group injected with saline, according to the research.
After a month, 75 percent of patients treated with epidural steroids said their leg pain had decreased by half or more, compared to 50 percent of those who received a saline solution and 42 percent of the patients that received etanercept.
However, after six months the outcomes shifted. Forty percent of patients taking saline and 38 percent of etanercept recipients reported a pain decrease of half or more, compared to 29 percent of the steroid group.
The effect of the steroids didn't last, Cohen said in a statement Monday, affirming the fact that steroids work, but not for very long.
Other studies that used twice the amount of etanercept as Cohen's team have found that it performs better than steroid injections, but Cohen says these higher doses of the drug have not yet been proven safe.
At higher doses, etanercept can suppress the immune system, Cohen said.