Opioids induce a variety of clinical relevant effects, which can be subdivided in being advantageous and/or even detrimental. One of the major consequences following opioid administration is that of analgesia, or antinociception. And while NSAIDs induce their antiniociceptive effect via cyclooxygenase (COX) inhibition, local anesthetics selectively block ion-channels, thus inhibiting the transmission of nociceptive efferent to the higher pain modulating centers in the CNS. Contrary, opioids bind to those areas, which not only are involved in transduction but also in the modulation and identification of painful afferences. Although the majority of opioids are able to induce a maximal analgesic effect, the dosages necessary to induce such a result differ significantly. For instance, an opioid like sufentanil
Figure 11-27. Intracellular changes following displacement of the opioid from the receptor site by an antagonist. Via enzyme phosphorylation of phosphokinase C (PKC) the N-methyl-D-aspartate (NMDA) receptor is activated resulting in an increased inward shift of Ca++-ions with an ensuing increase in neurotransmission of sensory afferents
Figure 11-27. Intracellular changes following displacement of the opioid from the receptor site by an antagonist. Via enzyme phosphorylation of phosphokinase C (PKC) the N-methyl-D-aspartate (NMDA) receptor is activated resulting in an increased inward shift of Ca++-ions with an ensuing increase in neurotransmission of sensory afferents needs a much lower dosage than the less potent opioid morphine. This is due to the higher affinity and intrinsic activity of sufentanil, suggesting that only a lesser portion of receptors needs to be occupied in order to induce the desired effect. However, a high analgesic potency necessarily does not reflect a better efficacy. This is because in certain painful conditions, some opioids are more efficacious than others. On the other hand, not all painful conditions, as the patient expresses them, can be treated successfully with an opioid. Therefore, before starting an opioid therapy it is mandatory to evaluate the kind of painful condition the patient has, use the specific opioids as indicated, and avoid those painful states where opioids are contraindicated or result in a lesser therapeutic effect. However, there is the general position:
In intense to severe, excruciating pain, opioids are the sole agents, which are able to induce sufficient analgesia
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