Presynatpic/postsynaptic inhibition of opioid analgesics  

through Gi coupling

presynaptic = dec. in Ca2+ influx --> substance P release/ inhibits release of NT)

postsynaptic = inc. K+ efflux --> hyperpolarization

Morphine

Mu receptor agonist

Analgesia:inc. pain tolerance/dec. perception of pain / sedation

 Respiratory depression: dec. response to inc. CO2 levels (give naloxone)

CV: minimal, except vasodilation so avoid in head trauma

Smooth muscle: cicular constricts :. dec. GI peristalsis, constipation, urinary retention, miosis

Cough suppression: antitussive

N/V: stimulates CTZ in brain

Histamine: increases release  

Meperidine

Full agonist opioid, like morphine/heroin

Characteristics: also antimuscarinic (no miosis, tachycardia, no GI/GU/ gallbladder spasm)

Active metabolite (normeperidine) a serotonin reuptake inhibitor that can cause seizures

Methadone

Full agonist opioid

Uses: in maintenance of opiate addicts

Codeine

Partial agonist opioid

Cough suppressant, analgesia, used in combo w/ NSAIDS

Nalbuphine, Pentazocine

mixed agonist/antagonist opioid

Kappa receptor agonist = spinal analgesia, dysphoria

Mu receptor antagonist = precipitation of w/drawl

Naloxone, Naltrexone 

Antagonists of opioids

Naloxone (IV) reversal for respiratory depression

Naltrexone (PO) decrease craving for EtOH and used in opiate addiction

SE's of opioid analgesics

Withdrawl from opioid analgesics

yawning, lacrimation, rhinorrhea, salivation, anxiety, sweating, goose bumps, muscle cramps, spasms

Can manage w/ methadone, clonidine (for autonomic SE's)

Loperamide

Dextromethorphan