2. OPIOIDS
DEFINITION
Any natural or synthetic compound
that imitates properties of natural
narcotics
Is an analgesic that works by binding
to opioid receptors, which are found
principally in the central nervous
system and the gastrointestinal tract.
The receptors mediate both the
beneficial effects, and the undesirable
side effects.
3. CLASSIFICATION
Natural opiates
Alkaloids contained in the resin of the opium poppy
(morphine, codeine, thebaine)
Semi-synthetic opiates
Created from the natural opioids (hydromorphone,
hydrocodone, oxycodone,oxymorphone,
desomorphine, diacetylmorphine (Heroin)
Fully synthetic opioids
Created from chemical compounds (fentanyl,
pethidine, methadone, tramadol and propoxyphene)
Endogenous opioid peptides
Produced naturally in the body (endorphins,
enkephalins, dynorphins, and endomorphins)
4. PHARMACOKINETICS
Distribution - Widely distributed throughout body
tissue; concentration in kidney, liver and spleen is
higher than that in plasma. Only a small fraction
enters brain rather slowly. Morphine crosses
placenta.
Metabolism - Extensively in the liver. Metabolic-
breakdown is the primary method of opioid
duration
Excretion - Metabolites are excreted by the
kidneys. A small fraction is excreted in stool
through the biliary tract.
Routes of administration - Oral, Transmucosal,
I.V (most rapid acting), I.M and S.C
5. PHARMACODYNAMICS
They reduce pain by binding to receptor sites (mainly mu-
receptors) in the central and peripheral nervous system. After
stimulation of receptors they mimic the effects of naturally
occurring opiates that are apart of the body's own pain relief
system.
Processing of pain information is inhibited by a direct spinal
effect at the dorsal horn, which involves presynaptic inhibition of
the release of tachykinins like substance P.
Emotional response to pain altered by opioid actions on the
limbic cortex
Act presynaptically to block Ca2+ uptake and consequently
inhibit neurotransmitter release. Opioids have been shown to
inhibit the release of many neurotransmitters, including
substance P, acetylcholine, norepinephrine, glutamate, and
serotonin.
6. PHARMACOTHERAPUTICS
Opioids are prescribed to relieve severe pain in
acute, chronic and terminal illnesses. They are
also used to reduce anxiety, control diarrhea and
suppress coughing.
ADVERSE EFFECTS
ACUTE
Miosis, Respiratory Depression, Nausea and
vomiting, Sedation, Skeletal muscle hypertonus,
Euphoria, Constipation, Vasodilatation, Urinary
retention, Bradycardia, Biliary Spasm, Morphine
poisoning.
CHRONIC
Tolerance, Physical Dependence and Apnea (in
newborns)
7. DRUG INTERACTIONS
Drugs that may effect opioid analgesic activity
include amitriptyline, diazepam, phenytoin, protease
inhibitors and rifampin.
Drugs that may be affected by opioid analgesics
include carbamazepine, warfarin, beta-adrenergic
blockers and calcium channel blockers.
Use of opioid agonists with other drugs that
decrease respiration, such as alcohol, sedatives,
hypnotic and anesthetics, increase the risk of
severe respiratory depression.
Taking tricyclic antidepressants, phenothiazines, or
anticholinergics with opioid agonists may cause
sever constipation and urine retention.
