Morphine

PD Properties

Full agonist at mu receptors

Actions

Reduce release of Substance P

Enhance reward pathway

Blocks release of multiple HPA axis hormones

Induces pupillary constriction

Direct stimulation of chemoreceptor trigger zone

Decrease vascular peripheral resistance

Respiratory depression (caused by decreased responsiveness to CO2+ other effects) rare in clinical dosing (caution with those with respiratory problems)

Muscular rigidity at higher doses

Blocks nocioception along several points of the pain transmission pathways

Inhibits GI motility

Increases bladder sphincter tone

Dilation of cutaneous blood vessels

Immunosuppression

Alters thermoregulation

PK Properties

Absorption: absorbed from GI tract, but significant 1st pass metabolism (bioavailability 25%), typically given parentally or intrathecal or via epidural

Distribution: PPB- 30%; does not concentrate in tissue

Metabolism: conjugation; 1 metabolite same action as parent (extends t1/2)

Elimination: via kidney