MORPHINE MAY MAKE PAIN LAST LONGER

Painkillers in the opium family may actually make pain last longer. Morphine treatment after a nerve injury doubled the duration of pain in rats, say scientists in a report during the proceedings of a meeting at the National Academy of Sciences.

The results raise the troubling prospect that in addition to having unpleasant side effects and addictive potential, opioids such as OxyContin and Vicodin could actually extend some types of pain. If a similar effect is found in people, “It suggests that the treatment is actually contributing to the problem,” says study co- author Peter Grace, a neuroscientist at the University of Colorado Boulder.

Scientists have known that opioid- based drugs can cause heightened sensitivity to pain for some people, a condition called opioid- induced hyperalgesia. The new study shows that the effects linger weeks after use of the drugs is stopped. Male rats underwent surgery in which their sciatic nerves, which run down the hind legs, were squeezed with a stitch — a constriction that causes pain afterward. Ten days after surgery, rats received a fiveday course of either morphine or saline.

Rats that didn’t receive morphine took about four weeks to start recovering, showing less sensitivity to a poke. Rats that got morphine took about eight weeks to show improvements — double the time. “That’s far bigger than we had anticipated. We were definitely surprised by that,” says Grace.