Pharmacological effects of morphine

PHARMACOLOGICAL EFFECTS OF MORPHINE

Antinociception

  • Severe cancer pain is tolerated more when morphine is given; relieves all types of pain, but most effective against continuous dull aching pain
    sharp, stabbing, shooting pain also relieved by morphine.
  • When morphine is given to a pain free individual :
    • Morphine causes miosis (pinpoint pupils) due to kappa receptor effect
    • Pinpoint pupils show still responsive to bright light
    • Oculomotor nerve (Cranial Nerve 3) is stimulated by kappa receptor site 
    • If kappa receptor is blocked, mydriasis from sigma effect will result
    • Atropine partially blocks effect indicating parasympathetic system involved
    • High doses (overdose situation) of morphine cause excitatory and spinal reflexes
    • High doses of many OPIOID agents cause convulsions  due to stimulation at sigma receptor

CNS

  • Is the primary site of action of morphine.
  • Morphine causes sedation effect, with no loss of consciousness,analgesia, euphoria, mood change mental cloudiness
  • Depending on the dose and its primary and continuous depression of respiration leads to : decrease rate, decrease volume and decrease tidal exchange.

CVS

  • Morphine produces vasodilatation
  • Morphine causes the release of histamine and
  • Suppression of central adrenergic tone and
  • Suppression of reflex vasoconstriction

GIT

  • Increase in tone and decrease in mobility leads to constipation
  • Decreased concentration of HCl secretion
  • Increased tone in stomach, small intestine, and large intestine delay of passage of food (gastric contents) so more reabsorption of water leading to constipation effect.

On smooth muscles

  • Biliary tract - marked increase in the pressure in the biliary tract
  • Increase due to contraction of Sphincter of Oddi urinary bladder
  • Tone of detrusor muscle increased, feel urinary urgency
  • Have urinary retention due to increased muscle tone where sphincter closed off

Bronchial muscle

  • Bronchoconstriction can result
  • Contraindicated in asthmatics, particularly before surgery

Uterus

  • Contraction of uterus can prolong labor

Neuroendocrine effect

  • Inhibit the release of gonadotropin-releasing hormone (GnRH) and corticotropin-releasing factor (CRF)
  • Decreasing circulating concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), ACTH, and beta endorphin. TSH unaffected.
Last modified: Wednesday, 16 May 2012, 4:59 AM