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Morphine
A potent opioid
- uses
- mechanism
- dose and half-life
- adverse drug reactions
- counter-indications and drug interactions
- metabolism and excretion
- dependency
Uses
- analgesia for severe pain (7-10)
- anxiolytic
- reduces sympathetic outflow
- vasodilation reduces cardiac filling pressures
- decreases MV02
Mechanism
1. Nociceptors
acts peripherally to decrease excitiability of sensory nerves
2. Spinal Cord
- prevents ascending pain transmission by binding presynaptic μ receptors, decreasing calcium influx and preventing vesicle release, especially glutamate
- binds postsynaptic μ receptors, increasing K+ influx and hyperpolarizes post-synaptic neurons
3. Supraspinal Sites
Disinhibition: activates μ receptors on descending GABA-releasing neurons in the periacqueductal gray in the midbrain, inhibiting them and inducing NE and 5-HT-production of pain inhibitory neurons. This leads to spinal block
4. Limbic System
affects emotional experience of pain, causing euphoria
Dose and Half Life
- half-life of 2 hours
Adverse Drug Reactions
short term
- constipation
- biliary colic
- respiratory depression
long term
Counter-Indications and Drug Interactions
Metabolism and Excretion
- metabolized by CP3A4 into M3G and M6G; variation
- metabolites (which don't cross the BBB) can be stored in muscle,
- excreted in urine