Opioids

Opioids are the most effective and widely used drugs in the treatment of severe pain. They act through G protein-coupled receptors. Four families of endogenous ligands (opioid peptides) are known. The standard exogenous opioid analgesic is morphine. Opioid agonists can activate central and peripheral opioid receptors. Three classes of opioid receptors (mu, delta, kappa) have been identified. Multiple pathways ofopioid receptor signaling (e.g., G(i/o) coupling, cAMP inhibition, Ca++ channel inhibition) have been described. The differential regulation of effectors, preclinical pharmacology, clinical applications, and side effects will be reviewed in this chapter.

Anticipating and treating opioid-associated adverse effects

Opioids are frequently avoided as viable tools in the management of pain due to perceived dangerous or untoward adverse drug events. Whilst they are relatively safe options for the treatment of pain, side effects and toxicities do exist and should be anticipated by the provider. The central nervous, gastrointestinal, genito-urinary, integumentary, metabolic/endocrine, cardiovascular, pulmonary, hepatic/renal, ocular and immune systems all manifest changes associated with opioid therapy. These adverse events, ranging from nuisance to therapy-limiting, are manageable when addressed quickly and appropriately. Opioids are safe and efficacious analgesics when these effects are considered.