Opioid agonists actions

Naloxone (75) is an opioid antagonist with slightly higher affinity for the mu subtype than kappa (A) in guinea-pig brain mu = 1.78 nM kappa = 27 nM delta = 1.72 nM) [96] and is widely used as a pharmacological tool to demonstrate the mechanism of action of opioid agonists. Despite much... 

The mechanisms of action of phencyclidine and ketamine are complex (Gorelick Balster, 1995). The drugs are non-competitive antagonists at NMDA receptors, and also bind to associated phencyclidine/sigma opioid receptors. They also have agonist actions at dopamine receptors, complex interactions with both nicotinic and muscarinic acetylcholine receptors and poorly understood interactions with noradrenergic and serotonergic systems. These multiple actions may combine to produce delirium and psychotic reactions. 

Small changes in molecular structure can reverse agonist actions of an opioid into antagonistic activity for one or several opioid receptors. Sometimes a molecule is produced that is an competitive antagonists at fx receptors but an agonist for k receptors. 

Nalmefene Revex) is a long-acting injectable pure opioid antagonist recently introduced in the United States. It binds all opioid receptors and reverses the effects of opioid agonists at those receptors. The onset of action is... 

Mechanism of Action An opioid agonist-antagonist that binds with opioid receptors in the CNS. Therapeutic Effect Alters the perception of and emotional response to pain blocks the effects of heroin and produces minimal opioid withdrawal symptoms. Pharmacokinetics Rapidly absorbed following IM administration. Protein binding Very high. Metabolized in liver. Primarily excreted in feces minimal excretion in urine. Half-life 2 hr... 

Mechanism of Action An opioid agonist that binds to opioid receptors in the CNS, reducing stimuli from sensory nerve endings and inhibiting ascending pain pathways. Therapeutic Effect Alters pain reception and increases the pain threshold. Pharmacokinetics ... 

Mechanism of Action An opioid agonist that binds at opiate receptor sites in central nervous system (CNS). Therapeutic Effect Reduced intensity of pain stimuli incoming from sensory nerve endings, alteringpain perception and emotional response to pain. Pharmacokinetics Rapidly absorbed. Protein binding 40%-50%. Extensively distributed. Metabolized in liver. Excreted in urine. Half-life 11 hr. 

Mecfianism of Action An opioid agonist that contains many narcotic alkaloids including morphine. It inhibits gastric motility due to its morphine content. Therapeutic Effect Decreases digestive secretions, increases gastrointestinal (GI) muscle tone, and reduces Gl propulsion. 

Widely prescribed tranquillizers - diazepam, nitrazepam, etc. Medication with both opioid agonist and antagonist actions Herbal sedative drug, with various forms derived from different parts of the plant... 

The actions described below for morphine, the prototypic opioid agonist, can also be observed with other opioid agonists, partial agonists, and those with mixed receptor effects. Characteristics of specific members of these groups are discussed below. 

Constriction of the pupils is seen with virtually all opioid agonists. Miosis is a pharmacologic action to which little or no tolerance develops (Table 31-3) thus, it is valuable in the diagnosis of opioid overdose. Even in highly tolerant addicts, miosis is seen. This action, which can be blocked by opioid antagonists, is mediated by parasympathetic pathways, which, in turn, can be blocked by atropine. 

Although all opioid agonists have some propensity to reduce shivering, meperidine is reported to have the most pronounced anti-shivering properties. Meperidine apparently blocks shivering mainly through an action on subtypes of the... 

Care should be taken not to administer any partial agonist or drug with mixed opioid receptor actions to patients receiving pure agonist drugs because of the unpredictability of both drugs effects reduction of analgesia or precipitation of an explosive abstinence syndrome may result. 

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