Morphine Essay Example
Morphine refers to a drug used in relieving moderate to severe postoperative and chronic pain. It belongs to a group of medicine known as analgesics (pain medicines) and acts on the central nervous system to relieve pain (Busse, 2006).
For morphine to produce an effect (such as pain relief), it has to be delivered to the specific cellular system in the body that mediates that mediates the effect. It has to interact with the neurons in the spinal cord and/or brain, which mediate the perception and sensation of pain in order to change the patient response to the painful stimulus. It can be administered orally through the mouth in form of a pill or liquid. It can also be administered through the rectum as a suppository and is also given by an injection with a hypodermic needle into the muscle (intramuscularly), into a vein (intravenously) or under the outer layer of skin (subcutaneously) (Busse, 2006).
Absorption and Distribution – gut / liver etc
Morphine is readily absorbed from the gastrointestinal tract. After absorption, it is rapidly distributed in the body including the brain, spleen, lungs, intestinal tract, liver, kidneys, and skeletal muscle. It has a large distribution volume and just one third of the circulating binds to the plasma proteins (Busse, 2006).
Metabolism and Excretion
After morphine is absorbed from the small intestines, it usually passes through the hepatic portal system to the liver whereby it is subjected to general metabolism by both conjugating as well as oxidative drug metabolizing enzyments (Busse, 2006). It takes 30 to 90 minutes for peak plasma drug concentration to be reached after oral administration and 15 to 20 minutes after intramuscular or subcutaneous administration. The main site of morphine metabolism is the liver, whereby it undergoes rapid glucuronidation. Its clearance from the system is very high and has a very short half life of about 2 hours. It is excreted in the urine within the first 24 hours.
Some of the drugs that interact with morphine are antipsychotic medications, antihistamines, alcohol, barbiturates, antidepressants, muscle relaxants, benzodiazepine sedatives, Monoamine oxidase inhibitors (MAOIs) and opiates or narcotics such as oxycodone and hydrocodone. The interaction may cause drowsiness, sedation, decreased motor skills, profound coma or sedation, hypotension, depression, and respiratory depression.
Morphine usually produce its major effect in the central nervous system mainly through k-,m 1-,m2 and d-receptors. m-1 receptors play a key role in decreased gastrointestinal activity, analgesia, pain modulation, euphoria, miosis, and respiratory depression (Busse, 2006). m 2 receptors play a key role in mental clouding, nausea drowsiness, and respiratory depression. d-receptors are involved in hallucinations, delusions, dysphoria and analgesia whereas k-receptors are involved in sedation, mild respiratory depression, dysphoria, and dieresis.
Busse, G. (2006). Morphine. New York: Infobase Publishing.
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