Opioids, including naturally occurring alkaloids (opiates derived from the poppy plant Papaver somniferum), semisynthetic compounds (chemically altered alkaloids), and synthetic agents, are potent analgesics and produce an intense euphoria associated with nausea; drowsiness; miosis; and a decrease in respiration, pulse, and blood pressure.
Opioids also are valued for their calming, antitussive, and antidiarrheal properties. Depending on the particular effect on opioid cell membrane receptors, they may be classified as agonists (morphine, heroin, methadone), partial agonists-antagonists (buprenorphine), or antagonists (naloxone, naltrexone). These drugs have led to many medical complications because of their abuse potential and their parenteral route of administration.
[...] Biomolecular Mechanisms of Action Opioids exert their effects on specific receptors for three distinct families of endogenous opioid peptides: enkephalins, endorphins, and dynorphins. In the central nervous system, three major classes of opioid receptors with unique selectivity and pharmacologic profiles have been identified: µ, and d. Subtypes of these major classes (µ1, µ2, d1, d2) have been elucidated primarily by the use of selective receptor antagonists. µ receptor activity is associated with the most prominent manifestations of morphine and heroin: respiratory depression, analgesia, euphoria, and the development of dependence. [...]
[...] In addition to these effects on opioid receptors, heroin causes the release of histamine, which may result in itching, scleral injection, and hypotension. High levels of tolerance develop rapidly with regard to respiratory depression, analgesia, sedation, vomiting, and euphoric properties. Little tolerance develops for miosis or constipation, so a heroin addict with an acutely painful medical condition may complain of insufficient analgesia despite pinpoint pupils. Cross-tolerance is common among opioids. From the patient's perspective, withdrawal from heroin is a dreaded clinical condition, a mix of emotional, behavioral, and physical signs and symptoms. [...]
[...] Other cardiac complications associated with opioid abuse include toxic cardiomyopathy, perivalvular abscess, abnormalities of the conduction system such as QT prolongation and ST-T wave changes, and cor pulmonale. The most common pulmonary complication is bacterial pneumonia, which is present in one third of injection drug users evaluated for fever. The risk for this infection probably results from a combination of factors, including hypoventilation, immune dysfunction, suppression of coughing, and aspiration during periods of clouded sensorium. Pulmonary hypertension can result from "talc granulomatosis," the development of diffuse pulmonary granulomas caused by the intravenous injection of foreign substances, most notably talc. [...]
[...] Neurologic complications of opioid abuse are infectious and noninfectious. Seizures, most often generalized, are the most common noninfectious complication. The cause of seizures includes overdose, with centrally mediated respiratory depression and hypoxia, and cerebral infarction. Meningitis, mycotic aneurysm, and abscesses (epidural, subdural, and brain) are well-described infectious conditions resulting from injection drug use. In HIV-infected patients, HIV-associated neurologic infectious and noninfectious diseases occur. Psychiatric conditions among opioid abusers are common and include alcohol abuse/dependence, major depression, phobic disorders, and antisocial personality, all of which have a greater than 15% lifetime prevalence. [...]
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