Opioid Analgesics Flashcards
28 slides
opioid analgesics purpose
To relieve moderate-to-severe pain.
endogenous opioid peptides
name the 3 families:
peptide function:
three families: endorphins, enkephalins, & dynorphins
- peptides control pain and inflammation, regulate immune system, GI function, cardiovascular responses
Mu
strong agonist, high affinity with mu receptors in the CNS
–severe pain***
– possible symptoms: sedation, respiratory depression, constipation
strong agonist common drugs
- hydromorphone
- meperidine
- methandone **
- morphine **
- tramadol **
mild to moderate agonists
- treat moderate pain
common drugs:
1. codeine
2. hydrocodone
3. oxycodone
4. propoxyphene
mixed agonist-antagonists function
- exhibit agonist and antagonist like activity at the same time
– ex: activate kappa receptions and block or partially activate mu receptors
-
mixed agonist-antagonists
strengths
Less risk of the side effects associated with mu receptors.
mixed agonist-antagonists
weaknesses
➢ May produce more psychotropic effects.
➢ Maximal analgesic effect may not be as great as strong mu agonists
antagonists
function
do not produce analgesia, used to treat opioid ODs and addiction
antagonist primary agent
naloxone
pharmacokinetics
where does metabolic inactivation take place?
primarily in the liver, partially in kidneys, lungs, and CNS
mechanism of action
name the 3
- spinal effects
- supraspinal [brain] effects
- peripheral effects
mechanism of function
functions
- decreased ascending (Afferent) pain transmission + activate descending (efferent) pathways that decrease pain (spinal and supraspinal effects)
- At peripheral sensory nerve endings, opioids decrease
excitability of the neuron and inhibit the neuron from initiating
transmission of painful stimuli toward the spinal cord (peripheral effects).
spinal effects
Inhibitory effect is mediated
by opioid receptors that are
located on both presynaptic
and postsynaptic membranes
of pain- mediating synapses
supraspinal effects
*goal is to decrease pain
1. opioids bind to specific receptors in the midbrain periaqueductal gray matter (PAG) and disinhibit descending pathways that decrease pain.
2. Increased activity of descending pathways travels through the ventromedial medulla (VMM) to reach the dorsal horn of the spinal cord.
3. Neurons in descending pathways release serotonin and norepinephrine onto dorsal horn synapses and inhibit the ability of these synapses to transmit
painful impulses to the brain.
peripheral effects
decreased peripheral nerve endings’ sensibility and inhibit neuron from sending pain signals to brain
clinical applications
when are they used
- acute mod to severe pain following surgery, trauma, myocardial infarction
- chronic pain [cancer]
- not effective in treating sharp and intermittent pain
how are opioids administered
- orally administered opioids work best when given at scheduled intervals
- patient-controlled analgesia
opioids side effects
► Mental slowing and drowsiness (sedative properties)
► Respiratory depression (slow the breathing rate)
—— Can be sever or even fatal in seriously ill patients
► Orthostatic hypotension
► GI distress
—–Nausea, vomiting, and constipation (due to its anti-peristaltic
action
addiction
When an individual repeatedly ingests certain substances for mood-altering and pleasurable
experiences, such as the heroin
tolerance
The need to progressively (periodically) increase the dosage of a drug to achieve a therapeutic effect (to provide adequate relief) when the drug is used for prolonged periods
tolerance mechanisms
▪ Receptor down-regulation (removed by endocytosis) and desensitization.
▪ Loss of communication between the opioid receptor and the G protein.
how long does tolerance last
Tolerance seems to last approximately 1 to 2 weeks after the drug is removed
when does tolerance begin
Begins after the first dose of the narcotic, but the need for increased amounts of the drug usually becomes obvious after 2 to 3 weeks of administration.
physical dependence
The onset of withdrawal symptoms when the drug is abruptly removed
physical dependence
Withdrawal symptoms become evident within 6 to 10 hours after the last dose of the drug, and peak on day 2 or day 3 after the drug has been stopped; last about 5 days.
- risk of addiction is low when opioids are used appropriately
opioid-induced hyperalgesia
Certain patients may fail to respond to opioids or may report increased pain sensitivity (hyperalgesia)
- pain may worsen when drugs are reaching peak effect
- pain may reduce when effects are minimal
methadone
Methadone
➢ Offers several advantages, such as milder withdrawal symptoms
buprenorphine
An alternative; a mixed agonist– antagonist
hyperalgesia PT implication
