Opioids, such as morphine, are effective and widely used drugs for the control of pain.
However, tolerance to opioids can develop with repeated administration (that is, higher and higher doses of the drug are required to achieve the same level of pain relief).
Nonetheless, there is some evidence to suggest that tolerance to opiods does not develop when they are used to treat individuals with diseases that are accompanied by inflammation.
Support for this hypothesis has now been provided by Christian Zöllner and colleagues from Charité--Universitätsmedizin Berlin, Germany, who found that peripheral tolerance to morphine did not develop in the chronically inflamed paws of rats.
Furthermore, blocking the action of endogenous opioid compounds in the inflamed tissue enabled tolerance to morphine to develop.
These data indicated that under conditions of chronic pain, endogenous opioid compounds prevent morphine from causing tolerance, inferring that the use of peripherally acting opioids for the prolonged treatment of inflammatory diseases such as chronic arthritis, inflammatory neuropathy, and cancer is not necessarily accompanied by opioid tolerance.
The journal article "Chronic morphine use does not induce peripheral tolerance in a rat model of inflammatory pain" was published in the Journal of Clinical Investigation on February 1, 2008.
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