Opioid selectivity for

Animal and human clinical studies demonstrate that both endogenous and exogenous opioids can also produce opioid-mediated analgesia at sites outside the CNS. Pain associated with inflammation seems especially sensitive to these peripheral opioid actions. The identification of functional p receptors on the peripheral terminals of sensory neurons supports this hypothesis. Furthermore, activation of peripheral preceptors results in a decrease in sensory neuron activity and transmitter release. Peripheral administration of opioids, eg, into the knees of patients undergoing arthroscopic knee surgery, has shown some clinical benefit. If they can be developed, opioids selective for a peripheral site would be useful adjuncts in the treatment of inflammatory pain (see Ion Channels Novel Analgesics). Moreover, new peripherally acting dynorphins may provide a novel means to treat visceral pain. 

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