Conventional painkillers, from aspirin to morphine, are not very effective at reducing neuropathic pain. Neuropathic pain is pain caused by the nervous system itself. It may be due to damage to the nerves, or other changes in the nervous system. Up to now, two types of drug have been used to treat neuropathic pain. These are drugs that are normally used to treat epilepsy (anti-convulsants) or depression (tri-cyclic anti-depressants). But these drugs are not fully effective, they don't help everyone, and they can have unpleasant side-effects.
A new drug has been found that appears to effectively reduce both chronic inflammatory pain and neuropathic pain in rats. It is so new that it hasn't got a name, and is just called A-317491. Researchers at the University of Iowa and Abbott Laboratories injected the drug into rats suffering chronic pain. Two groups of rats were used, one group in which chronic inflammatory pain had been caused by injecting an irritant, and one group in which neuropathic pain had been caused by pinching a nerve. The drug reduced their pain, with increasing doses giving increased reduction in pain. However, the drug had no effect on the kind of sharp, sudden pain caused by injury. The fact that this drug is selective in its effects is particularly important. It means that people with neuropathic or chronic inflammatory pain could be cured of those kinds of pain without becoming insensitive to normal sensations.
A-317491 appeared to cause fewer side effects than other drugs, and it did not reduce in effectiveness when given repeatedly. It may therefore be a much more effective treatment of chronic inflammatory pain and neuropathic pain than present drugs. However, it has not yet been tested in humans, so it is likely to be a long time before it is available from doctors.
If this drug works as well in humans as it does in rats, it will be a very important development for people with chronic pain.