Targeting pain and inflammation by peripherally acting opioids

INTRODUCTION Opioids can produce potent analgesia by activating opioid receptors outside the central nervous system, thus avoiding centrally mediated unwanted effects. Peripheral opioid receptors are expressed in peripheral sensory (dorsal root ganglion) neurons and can interact with exogenous or endogenous opioid ligands both in animals and in humans. Inflammation of peripheral tissue leads to upregulation of such opioid receptors and to local production of endogenous opioid peptides in immune cells. This article will summarize recent mechanistic, preclinical, and clinical findings.