Lecture 9: Pain Pharmacology Flashcards
What is the key difference between an anesthetic and an analgesic?
Anesthetics involve depressing all CNS characteristics, aka loss of all sensory modalities. Usually accompanied by LOC.
Analgesics are pain only, no LOC.
What is the gate-control theory?
Non-painful stimuli shut the gate to painful stimuli, preventing pain sensation from traveling to the CNS.
What do we use non-opioid medications for?
Adjuvants
First-line therapy for pain
Anesthesia
What are the side effects of corticosteroids?
Adrenal suppression
Appetite stimulation/weight gain
Cataracts formation
Impaired glucose metabolism
Edema
CHF
Osteoporosis
PUD
Bleeding
Mood changes
Steroid Psychosis
Joint degradation/atrophy at injection site with repeated injections.
What is the mechanism of action of corticosteroids?
Inhibition of phospholipase A2, which decreases the production of arachidonic acid and the inflammatory mediators.
What are the two pathways NSAIDs target?
COX-1
COX-2
What is the MoA of an NSAID?
Inhibition of the COX pathway. Subsequently inhibits prostaglandin formation.
Inhibits urate crystal phagocytosis (gout)
What does COX-1 inhibition commonly cause?
GI issues
Some prostaglandins are protective to mucosa which inhibit acid erosion
What does COX-2 inhibition commonly cause?
Decreases prostaglandins which therefore decrease inflammation, pain, fever
ALSO causes platelet aggregation and vasoconstriction, which is why celebrex has a cardiac black box warning.
What is the PK of an NSAID?
Low pH causes absorption by intestinal and gastric mucosa.
Binds to albumin
Conjugated to inactive metabolites, renal excretion.
What lab test should I order before giving someone NSAIDs?
Renal function test, to check GFR.
What are the other names for tylenol?
Acetaminophen/Paracetamol.
Scientific name: N-acetyl-p-aminophenol (APAP)
What is the MoA for Tylenol?
It is a selective COX inhibitor that generally targets COX-2.
Metabolites of APAP bind to TRPA-1 receptors, suppressing signal transduction of dorsal horn.
Why is tylenol an antipyretic?
COX enzyme reduction decreases formation for prostaglandin H2, which decreases E2 in hypothalamus (responsible for thermoregulation).
What is the max dose of tylenol in adults?
3000mg/day
What kind of toxicity does excessive tylenol cause?
Hepatotoxicity
When is NAPQI formed?
APAP metabolite formed after CYP metabolism.
Hepatotoxic!
What two conditions can cause hepatotoxicity with tylenol?
High dosages and/or low glutathione, which is caused by excessive ETOH.
What kind of lab test should I order prior to tylenol use?
Liver function tests.
What are other non-opioid medications?
Lidocaine patch/cream
Antispasmodics
Compounding pharmacy topicals
Membrane stabilizers
How do opioids work in general?
Alkaloid opiates mimic the action of endogenous endorphins (enkephalins) that are normally produced for analgesia by attaching to opioid receptors.
What kind of receptor interaction are opioids?
Ligands binding to G-Protein coupled receptors.
What are the 3 opioid receptor subtypes?
Mu (u)
Kappa (k)
Delta
What is the main opioid receptor subtype?
Mu: responsible for analgesia, respiratory depression, GI SE, sedation, and pruritis.
What do kappa receptor subtypes control?
Analgesia, but mainly the consciousness effects, like hallucinations, euphoria, etc.
What do delta receptor subtypes control?
Analgesia possible.
Might offset respiratory depression from mu receptor subtypes.
What NTs does an opioid affect? How?
GABA inhibition, which inhibits substance P.
Activates dopamine.
Activation of receptor inhibits adenylate cyclase, decreases intracellular cAMP. Overall effect is reducing flow of nociceptive flow.
What are the two types of Mu receptors? What do they control?
Mu1 is responsible for analgesia and physical dependence.
Mu2 causes euphoria, respiratory depression, and constipation.
Where can I find opioid receptors other than the brain?
Digestive tract & pre-synaptical peripheral sensory neurons.
What are NMDA receptors? What is the significance?
Responsible for memory, enhances pain stimuli, suppressing CNS sensitization.
Antagonizing the NMDA receptors can help decrease tolerance to opioids. (Methadone)
What exactly is opium?
Dried milky latex from the opium poppy plant.
What are the 5 schedules of controlled substances? What are most opioids under?
Schedule 1-5, with schedule 1 being the most dangerous/addictive substances, such as LSD, heroin, cocaine, ecstasy, cannabis.
Most opioids are schedule II.
What are the pros and cons of short acting opioids?
Pros:
Good starter drug
Good for PRN use
Commonly prescribed
Cons:
Quick tolerance
Easy to abuse bc commonly prescribed
Highs and lows
What are the pros and cons of long-acting opioids?
Pros:
Sustained releases, long acting
Cons:
High risk for abuse
Not for opioid naive patients
What are the general SE of opioids?
Constipation, drowsiness, pruritis, respiratory depression, Hyperhidrosis, mental blunting, edema, dental loss, hypotestoteronism
What two medications are commonly used as adjuvants for opioids?
Ibuprofen and APAP/tylenol
What is the difference between dependence and addiction?
Dependence is when discontinuing an opioid causes withdrawal effects.
Addiction is when there is a psychological dependence and preoccupation with obtaining a supply despite harm to themselves or others. High incidence of recidivism.
Is tolerance inevitable?
Yes, due to neuroadaptation of the receptor.
When does pseudoaddiction occur?
Patients with both malignant and chronic pain. Most often seen in under-treatment of pain.
What are some drugs we give for opioid withdrawal?
Methadone
Clonidine
Suboxone
What is the weakest opioid agonist?
Tramadol