Analgesia peripherally acting analgesics

Analgesia may be necessary for the after-effects of venepuncture or following therapeutic radiographic procedures. Peripherally acting analgesics, for example paracetamol, aspirin or ibuprofen should be sufficient. For pain that is more severe codeine may be necessary. See Chapter 12. 

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. 

They act as analgesics by inhibiting release of nociceptive neurotransmitters from primary afferent terminals as well as by depressing post-synaptic potentials on second order neurons. Opioid receptors are also present on some nociceptors and their expression and peripheral transport is increased upon peripheral inflammation. Peripheral opioid analgesia has been established in animal models. Although clinical studies have yielded mixed results so far, this field holds great promise. Despite side effects, such as euphoria, dysphoria, sedation, respiratory depression and obstipation and tolerance and dependence phenomena which arise upon... 

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