Opoid Analgesics
Terms
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- Thre main proteins cleaved to make endogenous opiods
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POMC
Proenkephalin
Prodynorphin - Three major biologically active opiods?
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Metenkephalin
Leu-enkephalin
Dynorphin A and B - the main receptor subtype of medical relevance
- mu
- Ion channel effects of opiod receptor activation
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increase potasium going out
decrease calcium coming in
net effect, inhibition both pre and post synaptically - Endogenous opiods and PCP
- endogenous opiods don't bind to PCP receptor sites!
- allodynia
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pain cause by previously inocuous stimuli
Prostoglandins sensitize nervers to sensation from stretch, head, chemicals - Drugs that can be combine with opiods to increased efficacy
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SSRI b/c serotonin modulates opiod interneurons in the dorsal colum
NSAIDS b/c prostoglandins sensitize nociceptors - Why you don't administer O2 to a patient on morphin
- Morphin depresses response to hypercapnia, so high C02 and carotid O2 are main resp drive. Giving pure O2 depresses drive and can cause resp failure
- Tx for first dose nausea with morphine
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Procholorperazine or chlorpromazine
Patients generally becomes refractory to nauses after initial dose - Morphines effect on autonomin system
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Depress sympathetic tone causing vasodilation
May cause orthostasis in normal people or worse in hypovolemic - GI effects of morphine
- Acts on nerve plexi and reduce propulsive contraction and increase spasm. Atropine lowers spasm so Atropine + morphine good anti-diarrheal
- Tx for actue morphine poisioning
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repeat injection of naloxone
Naloxone may precipitate withdrawal if patient is dependent on morphine - withdrawl from opiods vs withdrawls from ehtanol/barbits
- morphine withdrawls is less severe
- Codeine
- Fully absorbed orally unlike morphine (1/5) so is as effect as parenterally
- hydromorphone, oxymorphone
- like morphine but more potent
- oxycodone and hydrocodone
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used as antitussive and alagesic mixtures
equal to morphine but better absorbed orally - Heroin
- prodrug for morphine that rapidly, rapidly crosses BBB
- Leveorphanol
- optical isomer is dextromorpha
- Meperidine
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Demerol
Preferred opiate for OB because it has less constipation, urine retention, fetal resp depression and does not prolong labor - Mechanism of action for Meperidine
- Broken to meperidinic acid (analgesia) and normeperidine (excitatory) in the liver
- Naloxone with meperidine
- Naloxone blocks the analgesic properties of meperidine, but not the excitatory, so it can lead to convulsions
- Diphenoxylate
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Lomotil
Insoluable so no absorbed. With atropine, works as a good antidiarrheal with no CNS effects - Fentanyl
- 80 potentcy of morphine
- Methadone
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Morphine plus
Little higher oral absorbed
Longer half life
Less withdrawl - Propoxyphene
- slightly less effective than codeine but less addictive because you get toxic before you get high of codeine
- 1-acetylmethadol
- long lasting opiod in depot form used for treatment of opiate addiction
- long lasting opiate in depot form for tx of opiate addiction
- 1-acetylmethadol
- less effective than codein but it has less addictive potential as well
- propoxyphene
- Pentazocin
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kappa agonist, mu antagonist
less respiratory distress than all others
but causes nightmares etc at high doses.
May precpitate withdrawl in morphine addicts - Less respiratory effects than morphine but causes dysphoric effects at high doses
- pentazocin
- Naloxone vs Naltrexone
- Naloxone has no oral availability, naltrexone does with longer effects
- dextromethorphan
- antitussive with no opiod effects except at very high doses
- drug of choice for ob analgesia
- meperidine
- insoluble opiate used with atropine for diarrhea
- diphenoxylate
- 80x the potency of morphine
- fentanyl
- opiate of choice for cough
- dextromethorphan
- tx of autonomic symptoms during opiate withdrawl
- clonidine
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Which cause more biliary spasm
Codein, Morphine, Meperidine, Methadone - Morphine=Meth>Meperidine>Codein
- Duration of action for meperidine vs morphine vs methadone
- Methadone>Morphine>Meperidine
- Respiratory depression of meperidine vs morphine vs methadone
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All have same effect on respiratory depression
Mixed actors like pentazocine have less respiratory depression