Breakthrough in Morphine Tolerance

Study suggests eliminating peroxynitrite may prevent morphine tolerance.

"Blocking a substance called peroxynitrite, a potent oxidant that's formed when patients take morphine, can prevent the development of tolerance to the pain-relieving effects of the narcotic," according to findings published in the November issue of the Journal of Clinical Investigation.

Researchers at Saint Louis University of Medicine repeatedly dosed animals with morphine, and found that this "caused peroxynitrite to develop in the spinal cord, resulting in inflammation and damage to proteins and DNA in that area."

"[m]orphine and other opiate narcotics are the most powerful treatments for acute and chronic pain. However, their pain-killing effectiveness decreases quickly and significantly with repeated doses."

When the researchers eliminated peroxynitrite, "either by causing it to decompose once it formed, or by blocking it from forming in the first place," they discovered that this "prevented morphine tolerance."

They concluded, "We believe these findings represent a major breakthrough in understanding how tolerance to the pain-relieving action of morphine and other opiate medications develops -- and how it can be prevented from happening in the first place."