pain & analgesic drugs Flashcards
what is pain
a subjective unpleasant sensory or emotional experience associated with actual or potential tissue damage or described in terms of such damage
what is nociception
detection of noxious stimuli or stimuli that are capable of damaging tissue
4 processes in pain perception
1) transduction
2) transmission
3) perception
4) modulation
what is transduction
detection of physical stimuli into nerve input
- pain nerve endings
what is transmission
action potential travels along nerves to CNS
what is perception
the feeling/awareness of sensations in periphery
- happens in the cortex
what is modulation
CNS release inhibitors which decrease info going to brain
- less perception of pain
what is acute pain
- sudden onset
- subsides with treatment
- nociceptive stimulus causes
- sharp or dull (different receptors)
what is chronic pain
- long lasting (>6 weeks)
- persistent or recurring
- difficult to treat
- many different causes (not always from stimulus)
what is allodynia
pain from stimuli that’s not normally painful
what is hyperalgesia
heightened pain detection
what is causalgia
burning sensations
what is neuropathic pain
from damaged nerve fibers
somatic pain
superficial (skin, mucosal membranes, joints, bones)
visceral pain
vascular, organ, deep, respiratory
referred pain
occurs away from area of real cause
- heart attack felt in left arm
cancer pain
chronic, breakthrough
phantom pain
pain felt after amputation
success of analgesic drugs depends on type of pain
acute > chronic
two types of medication for pain
1) analgesic
2) anesthetic
analgesic medication
selectively blocks sensation of pain without blocking other symptoms or loss of consciousness
- not treating cause of pain
anesthetic medication
local anesthetic blocks all nerve conduction and all local sensations (pain, temperature, touch, etc)
general anesthetics cause loss of sensations and unconsciousness
type of analgesic drugs
opioids
opioid sites of action
1) higher centers (brain/cortex) to alter psychological response to pain
- brain detects pain, and regulates intensity and emotion around response
2) reduce neurotransmitter release from terminal pain fibers in dorsal horn of spinal cord
- modulation (dampen response and nociception sent to brain)
opioids general info
- drugs that bind to opioid receptors
- natural or synthetic
- agonists (bind to receptors and cause same effect of what normally binds to it
what is an opiate
any drug derived from opium (natural source - resin from poppy seeds)
- codeine, morphine
morphine is better at binding to receptor sites bc of slight difference in structure making it more effective
opioid receptor sites
all opioid analgesics are full agonists or partial agonists at mu or kappa receptors (for algesia)
there are mu, kappa, and delta opioid receptors
agonist receptors
drugs that bind to these receptors produce a cell response
- full agonist: good at binding and easily produce maximal response
- partial agonist: not as good at producing response
mu receptors
- very strong and present
- for algesia
- found in brain (cortex for feeling and perception of pain, and the thalamus, medulla, limbic system and amygdala for emotional response)
- spinal cord
kappa receptors
- less amount
- for algesia
- brain and spinal cord
- may cause dysphoria (unpleasant response and sensation) and hallucinations
pharmacological properties of opioids (important ones)
- analgesia: mu & kappa receptors, good for dull and persistent pain
- sedation and mental clouding: calmness and can’t think clearly
- euphoria and tranquility: dopaminergic pathways (drug abuse)
- antitussive: cough reflex depressed
- depression of resp center: less breaths/min, shallow breathing, drive for breathing decreases, potential for coma and stopping breathing
- constipation: increase GI muscle tone
other pharmacological properties of opioids
- nausea and vomiting
- miosis (pinpoint pupil): parasympathetic nerve
- tolerance and serious dependence (more drug needed for same pain relief effect)
- postural hypotension
- dilation of cutaneous blood vessels (warm skin)
- urinary urgency, difficulty urinating
- biliary colic and epigastric distress
opioid analgesic examples
- morphine (golden standard)
- methadone (longer action)
- fentanyl (non-naive pt)
- diamorphine (heroin)
- levorphanol
- hydromorphone
- oxycodone (not as strong, less risk for longer use)
- codeine (not as strong, less risk for longer use)
opioid indications
- alleviate mild-moderate-severe pain (often given with adjuvant analgesic agents to assist with pain relief - work at different areas along pain pathway)
- cough center suppression (codeine)
- treatment of diarrhea (loperamide)
- balanced anesthesia (fentanyl)
morphine general info
- acute and chronic pain
- the standard (other analgesics compared to it for dosing )
- 10 mg IM standard (equals to 0.1 mg fentanyl, 200mg codeine)
- IV, IM, SC, PO, intrathecal (CSF)
morphine metabolism
t1/2 = 2-4 hours
- extensive liver metabolism (first pass)
- inactivation
- PO dose is 30-40 mg
- liver disease: not as much metabolism = potential overdose if a higher PO dose taken to counteract first pass metabolism
morphine and pregnancy/breastfeeding
risk exists for physical dependance (of baby)
- can lead to physical reactions
- crosses placenta or enters breastmilk
short half life allows for timing with breastfeeding
analgesics and cancer pain
chronic pain requires ATC treatment (often combination of opioids, NSAIDs, and adjuvants)
- MS contin ATC (sustained release morphine around the clock)
breakthrough pain are transient episodes of pain while chronic pain is controlled (rescue medication)
WHO pain management ladder
1) pain: nonopioid and adjuvant if needed
2) increase in pain: opioid for mild to moderate pain and non opioid + adjuvant if needed
3) persisting/increasing pain: opioid for moderate to severe pain and non opioid + adjuvant if needed
NSAIDs
non steroidal anti inflammatory drugs
- most common non narcotic analgesic
adjuvants
- antidepressants (amitriptyline - elavil)
- antiseizure drugs (carbamazepine)
- glucocorticoids
morphine contraindications and cautions
- asthma or respiratory insufficiency (resp depression)
- hepatic dysfunction (caution for dosage - PO)
- elevated ICP (exacerbates condition)
- pregnancy
opioid adverse effects
- respiratory depression (hold next dose if <12 breath/min)
- CNS depression (sedation, dampen brain activity - possible coma)
- N & V (greatest on first dose)
- constipation (no tolerance development)
- hypotension (dilation of peripheral vessels - histamine release)
- itchiness (histamine release)
- urinary retention
- diaphoresis and flushing
- pupil constriction (miosis)
opioid interactions
CNS depressants
- cumulative effects
- antipsychotics, antihistamines, sedatives (benzodiazepines, barbiturates)
- ethanol/alcohol
moderate opioid analgesics
- codeine (3-methylmorphine)
- oxycodone
- buprenorphine
safer because the lower the effect on pain relief the lower the adverse effects
codeine
- agonist
- less algesia and resp depression
- liver metabolizes into morphine which gives more relief (~10% PO dose)
- unpredictable effect: don’t know how much will convert to morphine
- antitussive
- often combined: acetaminophen in tylenol, acetylsalicyclic acid in 222s or 292
oxycodone (oxycontin or percodan)
- agonist
- metabolism required for activation
- abuse potential
- common use with acetaminophen
- was overprescribed
naloxone (narcan, naltrexone)
- antagonist
- used for complete or partial reversal of respiratory depression from overdose
- opioid cannot bind to receptor bc naloxone is there
- short half life: level of naloxone may drop faster than opioid so may need to give another dose if s&s of overdose come back
- IM/SC/nasal spray
methylnaltrexone
- antagonist
- treat opioid induced constipation
- stop increase in muscle tone and decrease in peristalsis by attaching to receptor
- last resort after diet and laxatives
treating opioid addiction
1) methadone program (doesn’t give the same high but still satisfies craving, slowly lower the dose)
2) buprenorphine and naloxone (suboxone) SL
- b: can act as a partial agonist and give some degree of pain relief
- b: agonist-antagonist if morphine in system at the same time buprenorphine more likely to bind over morphine and give partial analgesic effect
- n: added to get around misuse, naloxone poorly absorbed and has high first pass metabolism but if someone tried to crush it and inject it then naloxone would take effect
opioid tolerance
common physiological result of chronic opioid treatment
- need more drug for same amount of relief
physical dependence of opioids
- abstinence syndrome will occur if drug is abruptly withdrawn
- drug must be administered to maintain normal function
- withdrawal symptoms not dangerous but unpleasant
- symptoms may take 2 weeks to get under control (anxiety, chills, hot flash, joint pain, lacrimation, cramping, vomiting, diarrhea, etc)
opioid nursing implications
- take oral form with food to minimize GI upset
- withhold if vital signs abnormal (esp respiratory rate)
- take with adequate fluid and fiber and stool softeners to minimize constipation
- change positions slowly (orthostatic hypotension)
