OPIOID Pharmacology : A Review

Pain is an unpleasant sensation that originates from ongoing or impending tissue damage. Management of different types of pain (acute, postoperative, inflammatory, neuropathic cancer) is challenging and yet the most frequent issue encountered by clinicians. Pharmacological therapy is the first line of approach for the treatment of pain and opioid drugs are prescribed for acute and chronic pain of moderate/severe intensity arising from malignant and nonmalignant diseases. The opium poppy was cultivated as early as 3400BC in Mesopotamia. The term opium refers to a mixture of alkaloids from the poppy seed. Opiates are naturally occurring alkaloids such as morphine or codeine and opioid is the term used broadly to describe all compounds that work at the opioid receptors. The physiologic modulation of noxious stimuli involves a highly complex system that integrates the actions of multiple opioid receptors and endogenous opioid peptides. Opioids produce their actions at a cellular level by activating opioid receptors. These receptors are distributed throughout the central nervous system (CNS) with high concentrations in the nuclei of tractus solitarius, peri-aqueductal grey area (PAG), cerebral cortex, thalamus and substantia gelatinosa (SG) of the spinal cord. They have also been found on peripheral afferent nerve terminals and many other organs. The efficacy of centrally applied opioids is well recognized, but when applied peripherally, for example in posttraumatic and inflammatory states, their actions are less reliable. Although they are associated with addiction, dependence, tolerance and abuse liability even then their place in pain management remains undebatable and unchallenged.