SM 236a, 240a, 244a - Pharmacology, Opioids, and Pain I, II, III Flashcards
Describe the action of buprenorphine on the mu opioid receptor
- Partial mu agonist = ceiling on agonism
- Binds the mu opioid receptor with high affinity
- Prevents other opioids from binding
- Makes naloxone reversal difficult in OD
- Use for opioid maintenance to treat addiction
What are the neurologic effects of opioid use?
- Analgesia
- Miosis
- Even in patients who are tolerant
What factors might increase a patient’s risk of UGI bleed when taking NSAIDs?
- Daily, long term use
- High doses of NSAIDs
- Combining NSAIDs with ASA
- ASA = aspirin
- Age
- Prior PUD or UGI bleed
- Anticoagulant use
- Alcohol or steroid use
Which NSAID is okay to use in patients with CV disease?
ASA (aspirin)
Butorphanol is classified as a mu opioid receptor…
A. Agonist
B. Antagonist
C. Agonist/Antagonist
D. Partial agonist
C. Agonist/Antagonist
- Analgesia is kappa mediated
- Does not have as much pain relieve as mu agonists, but fewer GI effects
- Can trigger withdrawl
- Do not use in opioid tolerant patients
What is Misoprostol?
- An agent that helps to protect the stomach lining from damage from NSAIDs
- Note – also causes diarrhea
A patient with oropharyngeal cancer is requiring management of pain due to tumor erosion into his mandible. A long duration opioid is desired in order to avoid his having to take medication frequently. Due to difficulty in swallowing, however, he can only consume liquids or tablets that are crushed and placed in applesauce. The best option is
- Sustained release morphine pills
- Sustained release oxycodone pills
- Hydromorphone pills
- Methadone
- Fentanyl lollipop
d. Methadone
Sustained release pills lose their duration when you crush them
Fentanyl lollipop is for acute pain; fast acting, short duration
Methadone is inherently long-acting; it has a long half life
Which opioids inhibit serotonin reuptake, leading to intense euphoria?
Merperidine
Tramadol
What is the difference between drug dependence and drug addiction?
- Dependence
- The patient will have physical withdrawal if the drug is stopped
- Addiction
- A psychological diagnosis involving misuse/abuse of the drug
What is the relevant metabolite of merperidine?
What are its effects?
Normeperidine
- 10 hour half life
- Causes CNS hyperactivity and seizures
- Cleared by the kidney
- Do NOT use in pts with renal failure
What is tolerance?
When prolonged use of a drug requires higher doses to achieve the same effect
How do opioid receptors vary person to person?
- Different density of mu, kappa, and delta receptors
- Due to different DNA
- Different variants of mu, kappa, and delta subgroups
- Due to splice variation
- These splice variants have different affinities
Result: Different opioids work differently for different people!
If a patient is having side effects but no analgesia, change the opioid
Increasing glycine and GABA in the CNS would have what effect on pain perception?
Glycine and GABA work through the descending pain pathway to intercept ascending nociceptive signals
More glycine and GABA = More descending action = decreased pain perception
Note: Prostaglandins inhibit the release of glycine and GABA
NSAIDs inhibit prostaglandins, and therefore increase glycine and GABA in the CNS
What is the role of COX-1 in protecting our stomach lining?
- Increase Mucous layer thickness
- Decrease pH gradient
- Increase Bicarbonate secretion
- Increase Mucosal blood flow
Naloxone is classified as a mu opioid receptor…
A. Agonist
B. Antagonist
C. Agonist/Antagonist
D. Partial agonist
B. Antagonist
Used for heroine/opioid overdose
Nonsteroidal antiinflammatory drugs exert their analgesic effect by
- Binding to prostaglandin receptors in peripheral inflamed tissue
- Inhibiting the action of prostaglandins on peripheral nerves
- Inhibiting the formation of prostaglandins
- Inhibiting the formation of arachidonic acid
- Inhibiting lipooxygenase
c. Inhibiting the formation of prostaglandins
Where does the sensory neuron (pain fiber) synapse with the secondary (central) neuron)?
Substantia gelatinosa (in the dorsal horn)
Morphine is classified as a mu opioid receptor…
A. Agonist
B. Antagonist
C. Agonist/Antagonist
D. Partial agonist
A. Agonist
What are the metabolites of oxycodone?
What provides analgesia – the parent drug or the metabolites?
Relevant metabolite = oxymorphone
14x more potent than oxycodone
Both the parent drug and the metabolie provide analgesia
Which somatosensory pathway is involved with pain, temperature, and crude touch?
Anterolateral pathway (including spinothalamic tract)
Describe the pain pathway from the site of tissue injury to the brain
-
Injured tisssue
- Prostaglandin, bradykinin, leukotriene
- Sensitized nociceptor detects pain, fires an action potential
- Pain travels up a sensory neuron to the dorsal horn
- Sensory neuron synapses with the secondary neuron in the dorsal horn
- Secondary neuron carries the pain signal to the brain
What protects our stomach lining from the acidic lumen?
Mucous layer containing HCO3
Which NSAIDs will not interfere with clotting?
COX2 selective NSAID
Ex: Celecoxib
Naltrexone is classified as a mu opioid receptor…
A. Agonist
B. Antagonist
C. Agonist/Antagonist
D. Partial agonist
B. Antagonist
Used to treat addiction
Why do NSAIDs work even when there is no inflammation?
NSAIDs prevent prostaglandin synthesis
- Prostaglandins are relesed in peripherl tissues due to inflammation, but they are also contituitively present in the CNS
- They normally work to amplify pain in the ascending pathway.
- Sensitize the second degree neurons to substance P and glutamate
- Inhibit the descending pathway by preventing glycine and GABA release
- They normally work to amplify pain in the ascending pathway.
- NSAIDs will prevent prostaglandins from having these effects on the CNS
Which NSAID will not increase a patient’s bleeding risk during surgery?
Celecoxib
COX2 selective inhibitor => will not interfere with platelet function
A patient comes to you suffering from pain following knee surgery 3 days ago. He reports that the opioid pain medication that he received from the orthopedic surgeon causes nausea and dysphoria but does nothing for his pain. He notes that a different opioid medication that he had from a prior surgery works well, and he requests you prescribe this for him instead.
What would the scientific justification be for prescribing this different opioid?
Different patients have splice variation in their mu, kappa, and delta receptrs
Different opioids have different affinities for these splice variants
Therefore, some opioids work better for some patients than others
What is the most common IV NSAID?
Ketorolac (no oral potency)
Same as ibuprofen, but ibuprofen is oral
What is pain?
Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
What is an opioid?
All drugs, both natural and synthetic, that bind to opioid receptors
- All opiates are opioids, but not all opioids are opiates
A transplant recipient is in the recovery room following a renal transplant surgery. The attending surgeon cancels the resident’s order to give a single dose of ketorolac for pain. The best reason for canceling the order is
- Ketorolac can cause microemboli in the new kidney
- Ketorolac can reduce blood flow to the new kidney
- Ketorolac can reduce sodium reabsorption in the new kidney
- Ketorolac can prolong postoperative ileus (cessation of peristalsis that occurs postop)
- Ketorolac can cause respiratory depression
b. Ketorolac can reduce blood flow to the new kidney
Ketorolac is an NSAID
NSAIDs inhibit prostaglandin synthesis, and will therefore prevent vasodilation in the afferent arteriole of the kidney
What sensations utilize the anteriolateral somatosensory pathways?
Pain, temperature, crude touch
Which NSAID may cause tinnitus (ringing in the ears)?
Aspirin (ASA)
Describe the mechanism of tramadol
- 2 mechanisms
- M1 metabolite is a mu opioid receptor agonist
- Parent drug blocks reuptake of 5-HT (serotonin) and norepinephrine
- Use caution if the patient is on other SSRIs
A patient in the ICU is recovering from a surgical resection of dead bowel. The patient is septic and requires hemodialysis three times a week. He is being given meperidine every 3 hours for control of his pain and to supplement his sedation. After two days on this regimen, you are called to his bedside because of seizures. The most appropriate therapy would be
- Naloxone to treat the meperidine induced seizure
- Benzodiazepines to treat the meperidine metabolite induced seizure
- Naloxone to control effects of delayed meperidine clearance
- Nalbuphine to antagonize the effect of the opioid while providing some analgesia
- Urgent dialysis to remove the accumulated meperidine
b. Benzodiazepines to treat the meperidine metabolite induced seizure
Normeperidine is a seizure-inducing metabolite of meperidine, normally cleared by the kidney
The seizures have nothing to do with the opioid recepotors, and should be treated as you would treat any seizure (with benzos)
What are the mechanisms of NSAID GI toxicity?
- Direct gastric irritation
- Most NSAIDs are weak acids
- Decreased cytoprotection via inhibition of COX1
- Decreased mucous layer thickness
- Increased pH gradient
- Decreased bicarb secretion
- Decreased mucosal blood flow
Describe the inflammatory prostaglandin synthesis pathway. Include the relevant enzymes and intermediates.
NSAIDS inhibit the synthesis of which of these intermediates?
- Cell injuory or other trigger causes phospholipid release
- Phospholipid -> Arachadonic acid
- Phospholipase A2
- Arachadonic acid -> Prostaglandin H2
- Cyclooxygenase (COX)
- NSAIDs act here to inhibit COX
- Prostaglandin H2 -> Tissue-specific prostaglandin
- Tissue specific PG synthase
How do prostaglandins enhance pain in the CNS?
Describe the mechanism
Prostaglandins act at the synapse between the nociceptor and the second-degree neuron in the dorsal horn
- Enhance substance P and glutamate release
- Sensitize the second degree neuron to substance P and glutamate
- Decrease glycine and GABA release from the descending pathway
- Descending pathway cannot effectively modulate the ascending pathway
These three mechanisms result in hyperalgesia
(Prevented by NSAIDs)
What do all NSAIDs have in common?
They inhibit cyclooxygenase (COX), the enzyme that makes prostaglandins
Which opioids might cause seizures?
- Morphine
- M-3-G metabolite produced by the liver may produce hyperalgesia, allodyina, myclonus, and seizure
- Merperidine
- Normeperidine metabolite has a 10 hour half life
- Cleared by the kidney - do not use in pts with renal failure
- Causes CNS hyperreactivity and seizures
- Normeperidine metabolite has a 10 hour half life
What are the differences between high lipohilicity opioids adn low lipophilicity opioids?
- High lipophilicity
- Fast onset, short duration
- Fentanyl, meperidine
- Low lipophilicity
- Slow onset, long duration
- Morphinne, hydromorphone
Hydromorphone is classified as a mu opioid receptor…
A. Agonist
B. Antagonist
C. Agonist/Antagonist
D. Partial agonist
A. Agonist
How do opioids affect the ascending pain pathway?
How do opioids affect the descending pain pathway?
- Ascending
- Opioids inhibit cellular adenylyl cyclase, which increases K+ currents and decreases Ca2+ currents
- This causes hyperpolarization of the neuron, and therefore decreased pain transmission
- Acts on the pre-synaptic and post-synaptic neurons in the dorsal horn
- Descending
- Opioids inhibit the inhibitors of the descending pathway
- Normally, inhibitory neurons prevent the descending pathway from affecting ascending pain transmission
- Opioids inhibit the GABA releasing inhibitory neurons in the periaqueductal grey and elsewhere
- This allows the descending pathway to block the ascending pain signals
Arachidonic acid is the precursor for which two substances?
Which enzymes are involved?
-
Arachidonic acid -> Prostaglandin H2
- Cyclooxygenase (COX)
- This is the pathway relevant to the pain pathway
- Arachidonic acid -> Leukotriene
- Lipooxygense
Which COX enzyme is involved in inflammation?
COX2
- Appears when inflammation/injury occurs - it is responsible for pain
- Most tissues
- Constitutitively active in some tissues
- CNS, kidney, uterus
- This means that selective COX2 inhibitors are not protective against kidney injury
What is dependence?
How is it different from tolerance?
-
Dependence
- Patient will have withdrawal if the drug is stopped
- The patient is physically dependent on the drug
- Tolerance
- Increased dose required for the same effect