Opioid receptor affinity for agonist-antagonist analgesics.

Analgesic medications are distributed to a variety of receptors within the central nervous system. Activity at these receptors (mu 1, mu, sigma, delta, kappa) results in both the beneficial pain-relieving effects of analgesics as well as undesirable side effects. The mixed agonist-antagonist class of analgesics offers the potential benefit of greater receptor site selectivity while diminishing the incidence of adverse sequelae, such as respiratory depression. Traditionally, it has been suggested that mixed agonist-antagonist medications may be associated with decreased analgesic effectiveness. However, newer agents of this mixed class may result in effective analgesia while diminishing the incidence of side effects.