May 23, 2001 ST. PAUL, MN – Help may be on the way for sufferers of chronic low back pain. Injections of botulinum toxin A, a drug based on the bacteria that causes food poisoning, eased the pain for patients in a study published in the May 22 issue of Neurology, the scientific journal of the American Academy of Neurology.
"More studies need to be done because we looked at only a small number of patients, but these results are promising for people with this problem," said study author and neurologist Bahman Jabbari, MD, of Walter Reed Army Medical Center in Washington, D.C.
Chronic low back pain costs an estimated 50 billion dollars per year to the U.S. economy, according to the study.
For the randomized, double-blind study, 31 patients with chronic low back pain were given injections of either botulinum toxin or a saline solution. The patients had experienced pain for at least six months, with an average of six years.
Three weeks after the injections, 73 percent of the people who received the drug said the amount of pain they were experiencing had gone down by 50 percent or more, compared to 25 percent of those who received the saline.
After eight weeks, 60 percent of those who received the drug still said their pain had gone down by 50 percent or more, compared to 13 percent of those receiving saline.
The patients also took a questionnaire before the study and after eight weeks that measured their ability to perform activities of daily life, such as walking, lifting and traveling. After eight weeks, 67 percent of the patients who received botulinum toxin showed improvement in their ability to function, compared to 19 percent of those who received saline.
None of the patients reported any side effects from the injections.
None of the patients who received botulinum toxin reported any worsening of pain or function after the injection. Two patients reported worsening of pain after the saline injection.
Six of the 10 people who received botulinum toxin were re-evaluated after six months. They reported that the drug's effect wore off after three to four months.
Before the study started, the patients were taking a variety of analgesic and anti-spasmodic drugs, including baclofen, non-steroidal anti-inflammatory drugs, anti-depressants and muscle relaxants. They were advised to continue their medications and not to change the dosage during the study.
Researchers aren't sure how the botulinum toxin works to reduce the pain; several factors may be contributing. The drug reduces the amount and severity of muscle spasms. It may also reduce pain by decreasing the input from sensory fibers or by acting on pain receptors, Jabbari said. Jabbari said more studies also need to be done to determine whether the drug will continue to help patients after repeated injections.
"That has been the case for patients who receive botulinum toxin injections for other disorders, such as the muscle disorders dystonia and spasticity, so hopefully that will be true for people with low back pain as well," he said.
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