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neuro:opioids:start [2026/02/15 02:42] – created andrew2393cnsneuro:opioids:start [2026/02/15 02:49] (current) – andrew2393cns
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 ====== Opioids ====== ====== Opioids ======
  
-Opioids are **mu-opioid receptor agonists** (or partial/mixed agonists) used for **moderate to severe pain**, anesthesia, perioperative analgesia, and palliative care.+Opioids are μ-opioid receptor agonists (or partial/mixed agonists) used for moderate to severe pain, anesthesia, and palliative care.
  
-They act centrally and spinally to reduce pain perception and emotional response to pain.+They decrease nociceptive transmission at both spinal and supraspinal levels.
  
 ---- ----
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 ===== Mechanism of Action ===== ===== Mechanism of Action =====
  
-Opioids bind to: +Receptor targets: 
-  * μ (mu) – analgesia, respiratory depression, euphoria, dependence + 
-  * κ (kappa) – analgesia, dysphoria +  * μ (mu) → analgesia, respiratory depression, euphoria, dependence 
-  * δ (delta) – minor analgesic contribution+  * κ (kappa) → analgesia, dysphoria 
 +  * δ (delta) → minor analgesic contribution
  
 Cellular effect: Cellular effect:
-  * ↑ Potassium efflux +  * ↑ Potassium efflux → neuronal hyperpolarization 
-  * ↓ Calcium influx +  * ↓ Calcium influx → ↓ neurotransmitter release 
-  * ↓ Neurotransmitter release (substance P, glutamate) +  * ↓ Substance P & glutamate transmission
-  * Hyperpolarization of pain pathways+
  
 ---- ----
  
-===== Core Clinical Effects =====+===== Opioid Comparison Table (Most Potent → Least Potent) =====
  
-  * Analgesia +^ Drug ^ Brand ^ Mechanism / Receptor Activity ^ Classification ^ Relative Potency (vs Morphine) ^ Key Clinical Pearls ^ 
-  * Sedation / euphoria +| [[neuro:opioids:sufentanil|Sufentanil]] | Sufenta | Full μ agonist | Full agonist | ~500x | Extremely potent; anesthesia | 
-  * Respiratory depression +| [[neuro:opioids:remifentanil|Remifentanil]] | Ultiva | Full μ agonist | Full agonist | 100–200x | Ultra-short acting (ester metabolism) | 
-  * Constipation (NO tolerance develops) +| [[neuro:opioids:fentanyl|Fentanyl]] | Duragesic, Sublimaze | Full μ agonist | Full agonist | ~100x | No histamine release; renal safe | 
-  * Miosis (pinpoint pupils) +| [[neuro:opioids:alfentanil|Alfentanil]] | Alfenta | Full μ agonist | Full agonist | 10–20x | Rapid IV onset | 
-  * Nausea / vomiting +| [[neuro:opioids:hydromorphone|Hydromorphone]] | Dilaudid | Full μ agonist | Full agonist | 4–7x | Less histamine than morphine | 
-  * Pruritus (histamine release)+| [[neuro:opioids:oxymorphone|Oxymorphone]] | Opana | Full μ agonist | Full agonist | ~3x | Potent oral agent | 
 +| [[neuro:opioids:oxycodone|Oxycodone]] | Roxicodone, OxyContin | Full μ agonist | Full agonist | ~1.5x | Good oral bioavailability | 
 +| [[neuro:opioids:morphine|Morphine]] | MS Contin | Full μ agonist | Full agonist | 1x (reference) | Histamine release; active metabolites | 
 +| [[neuro:opioids:hydrocodone|Hydrocodone]] | Hysingla ER | Full μ agonist | Full agonist | ~1x | Often combined with acetaminophen | 
 +| [[neuro:opioids:methadone|Methadone]] | Dolophine | Full μ agonist + NMDA antagonist | Full agonist | Variable | Long half-life; QT prolongation | 
 +| [[neuro:opioids:tapentadol|Tapentadol]] | Nucynta | Weak μ agonist + Norepinephrine reuptake inhibition | Dual mechanism | ~0.4x | Less serotonergic than tramadol | 
 +| [[neuro:opioids:tramadol|Tramadol]] | Ultram | Weak μ agonist + SNRI | Weak agonist | ~0.1x | Serotonin syndrome risk. Lowers seizure threshold | 
 +| [[neuro:opioids:codeine|Codeine]] | — | Weak μ agonist (CYP2D6 prodrug) | Weak agonist | ~0.1x | Variable metabolism | 
 +| [[neuro:opioids:meperidine|Meperidine]] | Demerol | Full μ agonist | Full agonist | ~0.1x | Normeperidine → seizures |
  
 ---- ----
  
-===== Classification & Comparison =====+===== Partial / Mixed Agonists (Lower Maximal Efficacy) =====
  
-^ Drug ^ Brand Examples ^ Receptor Activity ^ Relative Potency (vs Morphine) ^ Unique Clinical Pearls ^ Major Risks ^ +^ Drug ^ Mechanism ^ Classification ^ Key Feature ^ 
-| Morphine | MS Contin | Full μ agonist | 1x (reference) | Histamine release; active renally cleared metabolites | Hypotension, renal accumulation | +| [[neuro:opioids:buprenorphine|Buprenorphine]] | Partial μ agonist (high affinity) | Partial agonist | Ceiling effect; MOUD | 
-| Hydromorphone | Dilaudid | Full μ agonist | 4–7x | Less histamine than morphine | Potent respiratory depression | +| [[neuro:opioids:butorphanol|Butorphanol]] | κ agonist / μ antagonist | Mixed agonist | Ceiling effect | 
-| Oxycodone | Roxicodone, OxyContin | Full μ agonist | 1.5x | Good oral bioavailability | High misuse potential | +| [[neuro:opioids:nalbuphine|Nalbuphine]] | κ agonist / μ antagonist | Mixed agonist | Dysphoria | 
-| Hydrocodone | Hysingla ER | Full μ agonist | 1x | Often combined with acetaminophen | CYP3A4 interactions | +| [[neuro:opioids:pentazocine|Pentazocine]] | κ agonist / weak μ antagonist | Mixed agonist | Psychotomimetic effects |
-| Oxymorphone | Opana | Full μ agonist | 3x | Potent oral agent | Respiratory depression | +
-| Fentanyl | Duragesic, Sublimaze | Full μ agonist | 100x | No histamine; safe in renal failure | High overdose risk | +
-| Remifentanil | Ultiva | Full μ agonist | 100–200x | Ultra-short acting (ester metabolism) | Requires infusion | +
-| Sufentanil | Sufenta | Full μ agonist | 500x | Extremely potent (anesthesia) | Severe respiratory depression | +
-| Alfentanil | Alfenta | Full μ agonist | 10–20x | Rapid onset IV | Short duration | +
-| Methadone | Dolophine | Full μ agonist + NMDA antagonist | Variable | Long half-life; neuropathic pain benefit | QT prolongation | +
-| Meperidine | Demerol | Full μ agonist | 0.1x | Normeperidine metabolite (seizures) | Neurotoxicity | +
-| Codeine | — | Weak μ agonist (prodrug) | 0.1x | Requires CYP2D6 activation | Variable metabolism | +
-| Tramadol | Ultram | Weak μ + SNRI | 0.1x | Serotonin + NE reuptake inhibition | Seizures, serotonin syndrome | +
-| Tapentadol | Nucynta | μ agonist + NRI | 0.4x | Less serotonergic than tramadol | CNS depression | +
-| Buprenorphine | Subutex, Suboxone, Butrans | Partial μ agonist | High affinity | Ceiling effect; MOUD | Precipitated withdrawal | +
-| Butorphanol | Stadol | κ agonist / μ antagonist | Moderate | Ceiling effect | Withdrawal in dependent patients | +
-| Nalbuphine | Nubain | κ agonist / μ antagonist | Moderate | Ceiling effect | Dysphoria | +
-| Pentazocine | Talwin | κ agonist / weak μ antagonist | Weak | Psychotomimetic effects | Hypertension, dysphoria |+
  
----- +Partial and mixed agonists: 
- +  * Have ceiling effect on respiratory depression 
-===== Full μ Agonists (No Ceiling Effect) ===== +  * Can precipitate withdrawal in opioid-dependent patients
- +
-  * Morphine +
-  * Hydromorphone +
-  * Oxycodone +
-  * Hydrocodone +
-  * Oxymorphone +
-  * Fentanyl +
-  * Remifentanil +
-  * Sufentanil +
-  * Alfentanil +
-  * Methadone +
-  * Meperidine +
-  * Codeine (weak) +
- +
-These carry full risk of respiratory depression.+
  
 ---- ----
  
-===== Partial / Mixed Agonists =====+===== Clinical Effect Summary =====
  
-  * Buprenorphine (partial μ) +  * Analgesia 
-  * Butorphanol (κ agonist) +  * Sedation / euphoria 
-  * Nalbuphine (κ agonist) +  * Respiratory depression 
-  * Pentazocine (κ agonist) +  * Constipation (no tolerance) 
- +  * Miosis 
-Ceiling effect on respiratory depression. +  * Nausea / vomiting 
-Can precipitate withdrawal in opioid-dependent patients.+  * Pruritus (histamine mediated)
  
 ---- ----
  
-===== High-Yield Clinical Pearls =====+===== High-Yield Exam Pearls =====
  
-  * Tolerance develops to analgesia, sedation, and respiratory depression. +  * Full μ agonists → no ceiling effect. 
-  * Tolerance does NOT develop to constipation. +  * Partial agonists → ceiling effect. 
-  * Renal failure → avoid morphine. +  * Renal failure → avoid morphine and meperidine. 
-  * Methadone prolongs QT interval. +  * Methadone → QT prolongation. 
-  * Codeine and tramadol require CYP2D6 activation. +  * Tramadol → seizure + serotonin risk. 
-  * Tramadol increases serotonin → risk of serotonin syndrome. +  * Codeine → CYP2D6 dependent. 
-  * Avoid combining opioids with benzodiazepines or alcohol.+  * Fentanyl → safest in renal failure. 
 +  * Constipation persists despite tolerance.
  
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 Treatment: Treatment:
   * [[neuro:opioids:naloxone|Naloxone]]   * [[neuro:opioids:naloxone|Naloxone]]
- 
----- 
- 
-===== Withdrawal Symptoms ===== 
- 
-  * Yawning 
-  * Lacrimation 
-  * Rhinorrhea 
-  * Mydriasis 
-  * Diarrhea 
-  * Piloerection 
-  * Anxiety 
- 
-See: 
-  * [[neuro:opioids:withdrawal|Opioid Withdrawal]] 
  
 ---- ----
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 ===== Related Sections ===== ===== Related Sections =====
  
-  * [[eicosanoids:start|Eicosanoids (NSAIDs, COX inhibitors)]]+  * [[eicosanoids:start|Eicosanoids (NSAIDs)]]
   * [[neuro:cns_depressants:start|CNS Depressants]]   * [[neuro:cns_depressants:start|CNS Depressants]]
   * [[neuro:pain_modulation:start|Pain Pathways]]   * [[neuro:pain_modulation:start|Pain Pathways]]
neuro/opioids/start.1771123346.txt.gz · Last modified: by andrew2393cns