Opioid introduction and receptors 1
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Most of the opioid agonists in clinical use today are structural derivatives of what?
- Morphine and codeine alkaloids
- Which come from the latex of the opium poppy
Alkaloidal opioid agonists mimic the activity of two small endogenous pentapeptides, what are they called?
Enkephalins, endogenous opioid ligands, differ in structure only at the last amino acid in their 5 chain peptide, describe the difference:
- Leu-Enkephalin = TYR-GLY-GLY-PHE-“LEU”
- Met-Enkephalin is TYR-GLY-GLY-PHE-“MET”
What are enkephalins not used in the treatment of pain?
They are too short-lived to be of clinical use
What are the peptide analgesics on the market?
No peptide analgetic has yet found its way to market
What are the binding sites for alkaloidal opioids which mediate the analgetic response?
- u (mu, for morphine)
- K (kappa, for ethylketocyclazocine)
Enkephalin peptides prefer to bind to what type of opioid receptor?
Delta () receptor
Why is the Delta receptor that Enkephalins bind to called delta?
This receptor was first found in the vas “D”eferens
Why do opioids have a potential for abuse?
Due to the euphoric effects that opioid agonists produce
Patients using opioids for the treatment of ¬¬¬¬________ are much less likely to become addicted to these drugs than patients who need them for other reasons.
What is the major use-limiting side effect of opioids?
Why are opioid patients often under-medicated?
Due to careful practice to avoid abuse
What type of disease is Addiction?
- A primary, chronic neurobiologic disease with genetic, psychosocial and environmental factors influencing its development and manifestations
- involves a complex set of physiological and psychological responses to a drug’s chemical message
What are the two subclasses of Addiction?
- Tolerance and Dependence
- These two phenomena by themselves are not sufficient to define addiction
What is the definition of True addiction?
Strong psychosocial and genetic component, leading to drug craving and drug-seeking behavior in the absence of pain
What are the 4 C’s of drug additiction?
- Compulsive use
- Inability to Control the quantity taken
- Drug Craving
- Continued use despite negative consequences
Drug craving is a genetically based or learned behavior?
How long can Drug cravings last?
May last a lifetime
What is the main reason patients relapse after addiction?
What is the definition of Tolerance?
Increasingly larger dose of drug is required to produce the same degree of biological response that had previously been obtained with a lower dose
The mu receptor is what type of receptos?
Describe how analgesia and euphoria are produced by opioids at the mu receptor:
Mu receptor stimulation inhibits adenylate cyclase, which causes elevated cAMP levels that analgesia and euphoria
How does tolerance happen at the mu receptors?
- The body tries to maintain homeostasis by:
- Consistently depressed levels of cAMP stimulate the synthesis of new adenylate cyclase protein (upregulation) and a decrease in Gi synthesis
- mu receptor is absorbed back into the cell
How long must a patient be on an opioid to have Tolerance develop?
Chronically: several weeks or longer
What is the definition of Dependence?
Physiological need for drug to maintain "normal" functioning as defined by the adapted presence of the drug
Opioid withdrawal is usually severe, what are the main characteristics of it?
- Both physiological and psychological
- (physical and emotional distress)
(True/False)All patients on chronic opioid therapy will be dependent to some extent.
Tolerance and dependence apply to what activity of opioid action?
- Respiratory depressant actions
Tolerance and dependence DO NOT apply to what activities of opioid action?
What are the GI effects of opioids?
What drugs are often given concomitantly with opioids to counteract their GI activity?
Laxatives, such as Senna
Describe the pupillary response of opioids:
What is a diagnostic sign of opioid overdose in a patient experiencing respiratory distress and/or lack of consciousness or arousal?
Pin point pupils
What is a sign of signals the need for immediate antagonist therapy with opioid therapy?
Pin point pupils = Overdose
What is the Phenomenon of cross tolerance?
The ability of one compound to substitute for another and produce the same biological action
We say that one opioid is cross tolerant with another under what circumstance?
A person dependent on Opioid A can be suddenly switched to Opioid B without precipitating withdrawal symptoms
If two opioid analgetics are cross tolerant, what does this indicate?
- That they exert their agonist effects via the same receptor subtype
- i.e. one full mu agonist will be cross tolerant with another
Can an analgetic that acts at the K receptor be cross-tolerant with analgetics that work through the mu receptor?
- Must be the same receptor subtype
What is the risk of additiction to opioids for chronic pain patients?
What percent of addiction to opioids arise from genetic predisposition?
In addition to exhibiting tolerance and dependence, what must patients exhibit to be classified as addicted?
Must engage in destructive behavior patterns
Patients taking opioids for chronic pain will be _______ to and dependent on them
All patients taking opioids chronically can be classified as which of the following:
- Tolerant and Dependant
What is pseudoaddiction?
Patients with under-treated pain seek additional doses or “clock watch” until the time for their next dose of opioid
What is the difference between actual addiction and pseudoaddicted patients?
Pseudoaddiction disappears when their pain is relieved
What is hyperalgesia?
- Situation characterized by:
- New pain
- Exacerbation of existing pain
- Experiencing pain from non-painful events
Patients with hyperalgesia experience pain relief from what?
When dose of opioid is decreased, rather than increased
What should a clinician be mindful of when lower a dose in a hyperalgesia patient?
- Avoid precipitating withdrawal
- Consider rotating to a cross tolerant opioid to re-establish optimum pain control
- NMDA receptor antagonists may also have a therapeutic role
What is known to partially mediate the hyperalgesic response?
N-methyl-D-aspartate neurotransmitter system
Frequent office visits or telephone calls to the pharmacy, or requests for “interim prescriptions” of pain medication could sigsn of what?
- Worsening of pathology leading to untreated pain
- Disorganized lifestyle
- Physical/psychological dependence
Biochemical basis of euphoria is a __________ response.
Opioids that induce euphoria stimulate ______-coupled _____ receptors in the brain, leading to an inhibition of ________________.
A decrease in cAMP caused by opioids inhibits the release of what?
The inhibitory neurotransmitter GABA
GABA normally inhibits ________ release in the brain.
The decrease in GABA levels induced by mu receptor stimulation enhances _________release.
What aspect of opioid action causes euphoria?
Enhanced stimulation of dopamine receptors
Are people in pain believed to experience the euphoric effects of opioids?
What group of patients are thought to be able to feel euphoric effects of opioids?
Those not in pain
Individuals tolerant to mu agonists have significantly elevated levels of __________but _________ levels are kept low by high doses of opioid.
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