neuro pharm 6
Terms
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- Enkephalins
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– pentapeptides from proenkephalin, large polypeptide w/ multiple sequences of enkephalins
– Proenkephalin widely distributed in CNS, esp in areas associated w/ perception of pain
- YGGFM=Tyr-Gly-Gly-Phe-Met
- YGGFL= Tyr-Gly-Gly-Phe-Leu - Dynorphins
-
– 8-17 AA from prodynorphin
– distributed through CNS
- like proenkephalin - Endorphins
-
– 17-31 AAs from proopiomelanocortin (POMC)
– also has ACTH, melanocyte-stimulating hormone, β-endorphin, etc
– POMC limited to the arcuate nucleus and pituitary - μ receptor
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- supraspinal/spinal analgesia
– big resp depression
– causes euphoria and sedation
– big (+) reinforcement
– met-enkephalins and endorphins
– big GI tone
– morphine prototypical agonist
- only one that inhibits postsynaptic excitability - δ receptor
-
– supraspinal/spinal Analgesia
– plus or minus resp depression
– causes euphoria and dysphoria
– no (+) reinforcement
– leu-enkephalins
– no GI tone increase
– dynorphin prototypical agonist - κ receptor
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– spinal Analgesia
– some resp depression
– causes dysphoria (out of body)
– (+) reinforcement
– Dynorphins
– no GI tone increase
– leu-enkephalin is the prototypical agonist - Fentanyl
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- synthetic potent opiod agonist
– 15 – 30 minutes
– 100 times more potent than morphine
– Induction of general anesthesia
– Transdermal & sublingual for chronic pain - Heroin
-
- alkaloid potent opiod agonist
– Acetylmorphine (semi-synthetic)
– Fast acting - Morphine
-
- alkaloid potent opiod agonist
– 4 to 6 hrs
– Prototypical
– Reduces coughing - meperidine
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- synthetic potent opiod agonist Demerol
– 2-4 hrs, Reduces post-op shivering
– Does not reduce coughing
– Regional blocks (I.V. or I.M., epidural or intrathecal) - potent opioid agonists
-
- Tx of severe pain
– High affinity for μ-R
– Ultra-short acting - weaker opioid agonist
- Relieve moderate pain or post-operative analgesia
- Codeine
-
- alkaloid, weaker opioid agonist
– Lower abuse liability
– Moderate pain control
– Oxycodone similar structure and the more potent - mixed opioid agonists
- Useful for dependent patients & for post-op analgesia
- pentazocine
-
- mixed opioid agonists, synthetic Talwin
– κ-receptor agonist (dysphoria) w/ weak μ-receptor antagonist properties
– Moderate to severe pain - naloxone
-
- opiod antagonist
- 1-2 hrs (iv only) [t½ ~ 1 hr]
– Oral Availability 2%
– Non selective w/ μ>δ>κ – Acute tx of opioid intoxication (detox)
– Reverses overdose
– Precipitates withdrawal - naltrexone
-
- opiod antagonist
- 10 – 48 hours [t1/2 ~3 hr]
– Maintenance tx of opioid abuse
– Precipitates withdrawal à also used in detox
– Oral availability ~40% - dextromethorphan
- a synthetic Antitussive opioid
- Methadone
-
- synthetic opioid
– t1/2 ~14 hr
- Oral Availability ~92% - opioids + TCAs and & antipsychotics
- decrease seizure threshold and increase sedation + resp depression
- opioid plus MAOIs
- cause serotonin syndrome, HTN, hyperthermia, seizures, death (esp. meperidine)