mu receptor
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Abstract Objective: To review the literature on equianalgesic efficacy and better safety(less respiratory depression and gastrointestinal dysfunction) of oliceridine versus opioid analgesic in moderate to severe postoperative pain. Methodology: A comprehensive literature search was conducted in PubMed (January 2021 to March 2021) using keywords as ‘oliceridine’, ‘ligand biased mu receptor agonist’, ‘acute postoperative pain’, ‘conventional opioids’ and ‘morphine’. All English language full text pre-clinical and clinical research articles were searched. In addition, other data source was from ClinicalTrial. Gov. Data Synthesis: Oliceridine is a novel selective µ (mu)-receptor G-protein pathway modulator. G protein biased mu receptor agonists are a new class of opioids exhibiting analgesic properties at par to morphine with less respiratory depressant properties. Oliceridine a first-in-class intravenous (IV) analgesic has received the US FDA approval in August 2020, for management of moderate to severe acute pain in adults. The drug can be administered in cases where the pain is severe enough to require an intravenous opioid and when alternative treatments become inadequate. Oliceridine is an opioid agonist with a rapid onset of action within two to five minutes, was administered via clinician-administered bolus dosing, patient-controlled analgesia (PCA), or a combination of the two. Bolus dosing was initiated at 1 to 2 mg, with supplemental doses of 1 to 3 mg every one to three hours, as needed, based on individual patient need and previous response to oliceridine in management of acute post-operative pain. If oliceridine was administered via PCA, the loading dose was 1.5 mg, the demand dose was 0.5 mg, and the lockout interval (repeat dose)was six minutes. The clinically relevant concentration range of 0 to 35 ng/ml. It is indicated for short-term use only & limited to hospitals or other controlled clinical settings. Oliceridine requires no dosage adjustments in patients with renal impairment as well as in patient with significant medical complications. Therefore, opioids that bias towards G-protein and away from β arrestin signaling should produce analgesia with reduced side effects.

Opioids and stimulants are often used in combination for both recreational and non-recreational purposes. High-efficacy mu opioid agonists generally increase the behavioral effects of stimulants, whereas opioid receptor antagonists generally attenuate the behavioral effects of stimulants; however, less is known regarding the interactions between stimulants and opioids possessing low to intermediate efficacy at the mu receptor. The purpose of this study was to examine the role of an opioid's relative efficacy at the mu receptor in altering the behavioral effects of dextro(d-)amphetamine. To this end, opioids possessing a range of relative efficacy at the mu receptor were examined alone and in combination with cumulative doses of d-amphetamine on a test of open-field, locomotor activity in male rats. Levorphanol, buprenorphine, butorphanol, nalbuphine, (-)-pentazocine, (-)-metazocine, (-)-cyclazocine, (-)-NANM, and nalorphine increased the locomotor effects of d-amphetamine in either an additive or greater-than-additive manner according to an effect-additive model. Only the selective, high-efficacy kappa agonist, spiradoline, and the non-selective opioid receptor antagonist, naloxone, failed to increase the effects of d-amphetamine under the conditions examined. These data indicate that opioids possessing a large range of relative efficacy at the mu receptor, including those possessing very low relative efficacy, significantly increase the locomotor effects of d-amphetamine.

Methadone, a full opioid agonist at the mu-, kappa-, and delta-receptor, and buprenorphine, a partial agonist at the mu receptor, are first-line medications in opioid maintenance treatment. Transition from methadone to buprenorphine may precipitate withdrawal, and no accepted algorithm for this procedure has been developed. Current treatment strategies recommend transfer from methadone to buprenorphine predominantly in patients at low doses of methadone (30–40 mg/day). There are some reports indicating that transition from higher doses of methadone may be possible. A number of dosing strategies have been proposed to soften withdrawal symptoms and facilitate transfer including use of other opioids or medications and especially microdosing techniques for buprenorphine. The case series and studies available thus far are reviewed.

: Opioids are mu receptor agonists and have been an important part of pain treatment for thousands of years. In order to use these drugs appropriately and successfully in patients, whether to control pain, to treat opiate-induced side effects, or opiate withdrawal syndromes, a solid understanding of the pharmacology of such drugs is crucial. The most recognized full agonist opioids are heroin, morphine, codeine, oxycodone, meperidine, and fentanyl. Phenanthrenes refer to a naturally occurring plant-based compound that includes three or more fused rings. The opioids derived from the opium plant are phenanthrene derivatives, whereas most synthetic opioids are simpler molecules that do not have multiple rings. Methadone acts as a synthetic opioid analgesic similar to morphine in both quality and quantity; however, methadone lasts longer and in oral form, has higher efficacy, and is considered a diphenylheptane. Fentanyl is a strong synthetic phenylpiperdine derivative that exhibits activity as a mu-selective opioid agonist approximately 50 to 100 times more potent than morphine. Meperidine is another medication which is a phenylpiperdine. Tramadol is considered a mixed-mechanism opioid drug, as it is a centrally acting analgesic that exerts its effects via binding mu receptors and blocking the reuptake of monoamines. Some of the most common adverse effects shared among all opioids are nausea, vomiting, pruritus, addiction, respiratory depression, constipation, sphincter of Oddi spasm, and miosis (except in the case of meperidine). Chronic opioid usage has also established a relationship to opioid-induced hypogonadism and adrenal suppression. Physicians must be stewards of opioid use and use opioids only when necessary.

Los opioides son los analgésicos más potentes y efectivos de que disponemos en la actualidad. Su cara oscura la encarna el creciente aumento de pacientes adictos a su consumo en todo el mundo, principalmente en Estados Unidos. Desde el descubrimiento de los primeros opioides sintéticos, la industria farmacéutica se halla en busca de un analgésico que no genere tolerancia ni dependencia, ni efectos adversos respiratorios. La mayoría de los opiáceos son agonistas del receptor mu, cuya activación aumenta la disponibilidad sináptica de dopamina, neurotransmisor vehicular en circuitos de recompensa. Sin embargo, un cuarto receptor opioide ha sido descrito recientemente: el receptor de nociceptina/orfanina. Su activación inhibe la liberación de dopamina, evitando el refuerzo positivo que ocurre tras el consumo del fármaco. AT-121 es un agonista bifuncional MOP/NOP que ha sido probado en primates no humanos con resultados prometedores en cuanto a potencia analgésica, menores efectos secundarios sistémicos y menor tasa de adicción y abuso. Tales características hacen de esta molécula un arma esperanzadora en el tratamiento del dolor crónico o de la propia adicción a fármacos opioides. En los últimos años se han explorado distintos agonistas bifuncionales en roedores y primates no humanos con interesantes resultados; quedamos pues a la espera de futuras investigaciones en humanos. ABSTRACT Is AT121 the perfect opioid? Opioids are the most powerful and effective analgesics available today. Their dark side is reflected in the growing number of patients addicted to their use around the world, mainly in the United States. Since the discovery of the first synthetic opioids, the pharmaceutical industry has been searching for an analgesic that does not generate tolerance or dependence, nor adverse respiratory effects. Most opioids are mu receptor agonists, whose activation increases the synaptic availability of dopamine, a neurotransmitter that is a carrier in reward circuits. However, a fourth opioid receptor has recently been described: the nociceptin/orphanine receptor. Its activation inhibits the release of dopamine, preventing the positive reinforcement that occurs after drug consumption. AT-121 is a bifunctional MOP/NOP agonist that has been tested in non-human primates with promising results in terms of analgesic potency, fewer systemic side effects, and lower rate of addiction and abuse. Such characteristics make this molecule a hopeful weapon in the treatment of chronic pain or addiction to opioid drugs. In recent years, different bifunctional agonists have been explored in rodents and non-human primates with interesting results; we are therefore awaiting future research in humans.