Peripheral analgesic sites of action of anti-inflammatory drugs

Inflammatory signs and symptoms of redness, swelling, heat and pain are due to the effects of inflammatory mediators released during the inflammatory response. Depending on the type of injurious stimuli and the tissue involved, the array of mediators may differ but eicosanoids are involved in the genesis of inflammatory pain. They are responsible for the hypersensitisation of the nociceptors (allodynialhyperalgesia). The basic mechanism of analgesic action of nonsteroidal anti-inflammatory drugs results from the inhibition of prostaglandin synthesis (prostacyclin or PGE2), thus preventing nociceptor threshold lowering. Because there is a temporal hierarchy in the release of inflammatory mediators, there are several targets for the action of peripheral acting analgesics before and after the inhibition of prostaglandin synthesis. Blockade of the release and inhibition of inducible cyclooxygenase explain the analgesic action of glucocorticoids. Nimesulide also has an inhibitory action on the cascade of hypersensitising cytokines. Some analgesics, such as dipyrone, flurbiprofen or diclofenac, act directly upon ongoing inflammatory hypersensitisation. Those analgesics restore the nociceptor by stimulating the arginine/NO/cGMP/K(ATP) channel pathway.