Opioid Analgesics
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An opioid is a chemical that works by binding to opioid receptors, which are found principally in the central nervous system and the gastrointestinal tract. The receptors in these two organ systems mediate both the beneficial effects, and the undesirable side effects of opioids.
The analgesic (pain relieving) effects of opioids are due to decreased perception of pain, decreased reaction to pain as well as by increased pain tolerance. The side effects of opioids include sedation, respiratory depression, and constipation. Opioids can cause cough suppression, which can be both an indication for opioid administration or an unintended side effect. Physical dependence can develop with ongoing administration of opioids, leading to a withdrawal syndrome with abrupt discontinuation. Opioids can produce a feeling of euphoria, and this effect, coupled with physical dependence, can lead to the abuse of opioids by some individuals. However, abuse of opiods is uncommon in patients prescribed opioids for the treatment of pain.
Although the term opiate is often used as a synonym for opioid, it is more properly limited to the natural opium alkaloids occurring in the resin of the opium poppy and the semi-synthetic opioids derived from them.
Contents
*Classification & Mechanism Of Action:
1.Endogenous opioids
Dunniod-peptides that are produced in the body include:
* Endorphins
* Enkephalins
* Dynorphins
* Endomorphins
ß-endorphin is expressed in Pro-opiomelanocortin (POMC) cells in the arcuate nucleus and in a small population of neurons in the brainstem, and acts through µ-opioid receptors. ß-endorphin has many effects, including on sexual behavior and appetite. ß-endorphin is also secreted into the circulation from pituitary corticotropes and melanotropes. a-neoendorphin is also expressed in POMC cells in the arcuate nucleus.
enkephalin is widely distributed in the CNS; [met]-enkephalin is a product of the proenkephalin gene, and acts through µ and d-opioid receptors. [leu]-enkephalin, also a product of the proenkephalin gene, acts through d-opioid receptors.
Dynorphin acts through ?-opioid receptors, and is widely distributed in the CNS, including in the spinal cord and hypothalamus, including in particular the arcuate nucleus and in both oxytocin and vasopressin neurons in the supraoptic nucleus.
Endomorphin acts through µ-opioid receptors, and is more potent than other endogenous opioids at these receptors.
2.Opium alkaloids
Phenanthrenes naturally occurring in opium:
* Codeine,Morphine,Thebaine
Preparations of mixed opium alkaloids, including papaveretum, are still occasionally used.
3.Semisynthetic derivatives
* Diacetylmorphine (heroin),Dihydrocodeine,Hydrocodone,Nicomorphine,Hydromorphone,
Oxycodone,Oxymorphone
4.Synthetic opioids
a.Anilidopiperidines
* Fentanyl,Alphamethylfentanyl,Alfentanil,Sufentalin,Remifentanil
b.Phenylpiperidines
* Pethidine (meperidine),Ketobemidone,Allylprodine,Prodine,PEPAP
c.Diphenylpropylamine derivatives
* Propoxyphene,Dextopropoxyphene,Bezitramide,Methadone,
* Levomethadyl Acetate (LAAM)
* Loperamide (used for diarrhoea, does not cross the blood-brain barrier)
* Diphenoxylate (used for diarrhoea, does not appreciably cross the blood-brain barrier)
d.Benzomorphan derivatives
* Dezocine,Petazocain,Phenazocain
e.Oripavine derivatives
* Buprenorphine,Dihydrophene,Etrophine
f.Morphinan derivatives
* Butorphanol,Nalbuphine,Levorphanol,Levomethophan
5.Others
* Lefetamine,Meptazinol,Tilidine,Tramadol
6.Opioid antagonists
* Nalmefene,Naloxone,Naltrexone
Adverse Effect:
nausea and vomiting, drowsiness, itching, dry mouth, miosis, and constipation.
dose-related respiratory depression (especially with more potent opioids), confusion, hallucinations, delirium, urticaria, hypothermia, bradycardia/tachycardia, orthostatic hypotension, dizziness, headache, urinary retention, ureteric or biliary spasm, muscle rigidity, myoclonus (with high doses), and flushing (due to histamine release, except fentanyl and remifentanil)
The analgesic (pain relieving) effects of opioids are due to decreased perception of pain, decreased reaction to pain as well as by increased pain tolerance. The side effects of opioids include sedation, respiratory depression, and constipation. Opioids can cause cough suppression, which can be both an indication for opioid administration or an unintended side effect. Physical dependence can develop with ongoing administration of opioids, leading to a withdrawal syndrome with abrupt discontinuation. Opioids can produce a feeling of euphoria, and this effect, coupled with physical dependence, can lead to the abuse of opioids by some individuals. However, abuse of opiods is uncommon in patients prescribed opioids for the treatment of pain.
Although the term opiate is often used as a synonym for opioid, it is more properly limited to the natural opium alkaloids occurring in the resin of the opium poppy and the semi-synthetic opioids derived from them.
Contents
*Classification & Mechanism Of Action:
1.Endogenous opioids
Dunniod-peptides that are produced in the body include:
* Endorphins
* Enkephalins
* Dynorphins
* Endomorphins
ß-endorphin is expressed in Pro-opiomelanocortin (POMC) cells in the arcuate nucleus and in a small population of neurons in the brainstem, and acts through µ-opioid receptors. ß-endorphin has many effects, including on sexual behavior and appetite. ß-endorphin is also secreted into the circulation from pituitary corticotropes and melanotropes. a-neoendorphin is also expressed in POMC cells in the arcuate nucleus.
enkephalin is widely distributed in the CNS; [met]-enkephalin is a product of the proenkephalin gene, and acts through µ and d-opioid receptors. [leu]-enkephalin, also a product of the proenkephalin gene, acts through d-opioid receptors.
Dynorphin acts through ?-opioid receptors, and is widely distributed in the CNS, including in the spinal cord and hypothalamus, including in particular the arcuate nucleus and in both oxytocin and vasopressin neurons in the supraoptic nucleus.
Endomorphin acts through µ-opioid receptors, and is more potent than other endogenous opioids at these receptors.
2.Opium alkaloids
Phenanthrenes naturally occurring in opium:
* Codeine,Morphine,Thebaine
Preparations of mixed opium alkaloids, including papaveretum, are still occasionally used.
3.Semisynthetic derivatives
* Diacetylmorphine (heroin),Dihydrocodeine,Hydrocodone,Nicomorphine,Hydromorphone,
Oxycodone,Oxymorphone
4.Synthetic opioids
a.Anilidopiperidines
* Fentanyl,Alphamethylfentanyl,Alfentanil,Sufentalin,Remifentanil
b.Phenylpiperidines
* Pethidine (meperidine),Ketobemidone,Allylprodine,Prodine,PEPAP
c.Diphenylpropylamine derivatives
* Propoxyphene,Dextopropoxyphene,Bezitramide,Methadone,
* Levomethadyl Acetate (LAAM)
* Loperamide (used for diarrhoea, does not cross the blood-brain barrier)
* Diphenoxylate (used for diarrhoea, does not appreciably cross the blood-brain barrier)
d.Benzomorphan derivatives
* Dezocine,Petazocain,Phenazocain
e.Oripavine derivatives
* Buprenorphine,Dihydrophene,Etrophine
f.Morphinan derivatives
* Butorphanol,Nalbuphine,Levorphanol,Levomethophan
5.Others
* Lefetamine,Meptazinol,Tilidine,Tramadol
6.Opioid antagonists
* Nalmefene,Naloxone,Naltrexone
Adverse Effect:
nausea and vomiting, drowsiness, itching, dry mouth, miosis, and constipation.
dose-related respiratory depression (especially with more potent opioids), confusion, hallucinations, delirium, urticaria, hypothermia, bradycardia/tachycardia, orthostatic hypotension, dizziness, headache, urinary retention, ureteric or biliary spasm, muscle rigidity, myoclonus (with high doses), and flushing (due to histamine release, except fentanyl and remifentanil)
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