Friday, June 20, 2008

Morphine and Other Opioid Drugs

An opioid is a chemical substance that has a morphine-like action in the body. The main use is for pain relief. These agents work by binding to opioid receptors, which are found principally in the central nervous system and the gastrointestinal tract. The receptors in these two organ systems mediate both the beneficial effects, and the undesirable side effects.
Amongst analgesics are a small number of agents which act on the central nervous system but not on the opioid receptor system and therefore have none of the other (narcotic) qualities of opioids although they may produce euphoria by relieving pain - a euphoria that, because of the way it is produced, does not form the basis of morbid seek orientation, habituation, physical dependence, or addiction.


Clinical use

Opioids have long been used to treat acute pain (such as post-operative pain). They have also been found to be invaluable in palliative care to alleviate the severe, chronic, disabling pain of terminal conditions such as cancer. Contrary to popular belief, high doses are not required to control the pain of advanced or end-stage disease, with the median dose in such patients being only 15mg oral morphine every four hours (90mg/24 hours), i.e. 50% of patients manage on lower doses, and requirements can level off for many months at a time despite the fact that opioids have some of the greatest potential for tolerance of any category of drugs.

In recent years there has been an increased use of opioids in the management of non-malignant chronic pain. This practice has grown from over 30 years experience in palliative care of long-term use of strong opioids which has shown that addiction is rare when the drug is being used for pain relief. The basis for the occurrence of iatrogenic addiction to opioids in this setting being several orders of magnitude lower than the general population is the result of a combination of factors. Open and voluminous communication and meticulous documentation amongst patient, any caretakers, physicians, and chemists (pharmacists) is one part of this; the aggressive and consistent use of opioid rotation, adjuvant analgesics, potentiators, and drugs which deal with other elements of the pain (NSAIDS) and opioid side effects (stimulants in some cases, antihistamines) both improve the prognosis for the patient and appear to contribute to the rarity of addiction in these cases.

Common adverse reactions in patients taking opioids for pain relief:

These include: nausea and vomiting, drowsiness, dry mouth, miosis, and constipation. Fortunately, most of these are not a problem.

Infrequent adverse reactions in patient taking opioids for pain relief:
These include: dose-related respiratory depression (see below), confusion, hallucinations, delirium, urticaria, hypothermia, bradycardia/tachycardia, orthostatic hypotension, dizziness, headache, urinary retention, ureteric or biliary spasm, muscle rigidity, myoclonus (with high doses), and flushing (due to histamine release, except fentanyl and remifentanil).

Find out more about Opioid in Wikipedia

1 comment:

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