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What are the Endogenous Opioids and their targets receptors?
- Endorphins - mu receptors
- Enkephalins - delta receptors
- Dynorphins - kappa receptors
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Opioid MoA
- - inhibits neurotransmission at synapse
- - decrease presynaptic release
- - decrease postsynaptic excitability
- - decrease substance P release at Spinal Cord
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Opioid - Uses
- - severe pain managements
- - cancer, labor (cross placenta, can cause flaccid baby syndrome)
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Opioids - Adverse Effects
- sedation
- constipation
- respiratory depression/muscle suppression
- nausea & vomiting
- addiction/abuse/dependence/tolerance
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Morphine
- mu receptors agonist
- Pros:
- no ceiling effects
- patient-controlled analgesia
- Use:
- Adjunct in anesthesia
- pulmonary edema
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Methadone
- mu receptor agonist
- NMDA antagonist
- monoamine reuptake inhibitor
- Use:
- rehabilitation of other drugs
- Cons:
- prolong QT interval & arrhthymia
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Fentanyl
(Sufentanyl, Alfentanyl, Remifentanyl)
- mu receptor agonist
- Use:
- adjunct in anesthesia
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Hydromorphone, Oxymorphone
- mu receptor agonist
- more potent than morphine
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Meperidine
- mu receptor agonist
- has anti-cholinergic effects
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Oxycodone
- mu receptor agonist
- has ceiling effect, dose dependent
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Codeine
- mu receptor agonist
- less potent than morphine, but converts to morphine in body by CYP2D6
- (there is a genetic defect in caucasians that lack this enzyme, Codeine doesn't work)
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Dextromethorphan
- mu receptor agonist
- NO analgesic effects and addictive potentials
- less constipations
- Use: Anti-tussive (cough medications)
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Nalbuphine
Nalorphine
Levallorphan
- k agonist, mu antagonist
- has ceiling effect
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Buprenorphine
- k agonist, mu antagonist
- Use: rehabilitation programs (alternative to Methadone)
- Cons: hallucination, nightmare & anxiety when used with Pentazocine & Nalbuphine
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Tramadol
Tapentadol
- mu-partial agonist
- block 5-HT & NE reuptake (prolong effects)
- Cons:
- Seizure (prolonged NE, avoid MAO inhibitors)
- Serotonine syndrome (prolong 5-HT)
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Naloxone (short acting)
Naltrexone (long acting)
Nalmefene (IV only)
Methylnaltrexone
- opioid ANTAGONIST
- Uses:
- Opioid overdose
- alcohol & opioid dependence
- opioid-induced constipation
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