Opioids: A review

Abstract

Recent discoveries in opioid pharmacology help explain the enormous variability in clinical responses to these powerful analgesics. Although there is only one m opioid receptor gene, splice variants of that gene's expression result in a panoply of different functioning receptors. Other sources of variable response include polymorphisms in the m opioid receptor regulatory region, and pharmacokinetic differences because of cytochrome P-450 mono-oxygenase heterogeneity. Analgesic tolerance is likely the key phenomenon limiting the benefit of opioids. A plethora of intracellular pathways affects this. Among them are the N-methyl-D-aspartate receptor, protein kinase C gamma activity, nitric oxide synthase, and GM1 ganglioside content of the neuronal membrane. Clinical studies undercut the routine use of meperidine in most settings. Other studies have shown better ways to diminish opioid side effects.

Advances in opioid pharmacology

“…The relatively conserved intracellular loops and distinctive C-terminal tails help account for the overall general similarities, as well as for the type-specific differences that occur in intracellular signalling via G-coupled adenylyl cyclase inhibition, ion channel modulation, and mitogen-activated protein (MAP) kinase activation. Activation of all three receptors leads downstream to decreased neurotransmitter release and nociceptive impulse propagation [23,24].…”

“…Dimerization might result in varied individual response and incomplete cross-tolerance and may be the basis for the utility of opioid rotation for chronic use, such as for cancer pain. The relevance of alternatively spliced opioid receptor variants [24,17] and dimerization is still controversial.…”

Acute postoperative pain relief with immediate-release tapentadol: randomized, double-blind, placebo-controlled study conducted in South Korea

“…Most opioids used in clinical practice produce analgesia by activating m-opioid receptors on neurons within the pain transmission pathway 15 . However, these treatments are commonly associated with adverse effects, including nausea, vomiting, constipation, dizziness, and somnolence 16 , which can lead to undertreatment of the pain, in an attempt to minimize these events.…”

Recent and Emerging Trends in Pharmacotherapy of Neuropathic Pain

“…Apart from these agents, drugs like opioids (Morphine, Oxycodone, Methadone, Levorphanol, Tramadol etc.) [14,15,16] also have an established role in its treatment. The above drugs have been used for the management of various conditions like diabetic neuropathy, post herpetic neuralgia and other neuropathic pain syndromes.…”