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Medsci305 > Lectuer 16: analgesics > Flashcards

Lectuer 16: analgesics Flashcards

1
Q

What is pain?

A

-unpleasant sensory and emotional experience assoc with tissue damage or non tissue damage

  • subjective, difficult to quantify
  • similar harm can vary between patients
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2
Q

What must health professionals be aware of with regards to patient and pain?

A

accept patients response to pain

  • be observant
  • show empathy
  • consider if injury matches the level of pain reported
  • know the personality of the patient
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3
Q

How is pain management carried out?

A

-must be individualised to patient based on cause, severity of pain and chronicity

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4
Q

What is the Nociceptive pain pathway?

A
  • begins with tissue damage either due to mechanical, chemical or chemical hurt
  • pain signals are generated and are sent to the dorsal horn, then CNS
  • when the brain receives the signal, it responds by sending a descending inhibtion to relieve the pain message.
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5
Q

What does the nociceptive pathway tell us?

A
  • that there is more than one way to stop the pain.

- therefore local anaesthetis can block the nerve transmission at two sites

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6
Q

What are other possibilities for treating pain?

A
  • reduce signals at local site
  • reduce signals transffered to CNS
  • enhance descending inhibition pathway
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7
Q

What are non-pharmacological alternatives to treating pain?

A
  • transcutaneous electrical nerve stimulation
  • electrica stimulation to manage the pain
  • relaxation therapy (can reduce pain from scale 10 to scale 3)
  • nerve block
  • acupuncture: may induce activation of endogenous opiod system
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8
Q

What is TENS?

A

transcutaneousl electrical nerve stimulation

-electrodes are placed on skin to generate an electrical force that will help to relieve the pain

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9
Q

What are analgesis?

A
  • drugs that mediate pain relief

- we use different drugs to treat different types of pain e.g. for mild-mod pain we use mild drugs.

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10
Q

Why is it important to save the stronger drugs for more severe pain?

A

this increases the pain tolerance and will also help to manage the pain feelings

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11
Q

What are the two most common classes of analgesics?

A

Opioids and non-narotics

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12
Q

What are opioids?

A
  • substances (exogenous or endogenous) which bind to opiiod receptors
  • pharmacologically similar to opium or morphine
  • e.g. codeine, morphine, tramadol,
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13
Q

What are endogenous opioids?

A

-opioids which are naturally relied from the human body and can bind to receptors

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14
Q

What are exogenous opioids?

A

opioids which you have to take as either a drug or other material

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15
Q

What are primary analgesics used for?

A
  • cough suppressants and to control diarrhoea
  • hence elderly often use opioids to treat other medical conditions
  • provides analgesic without anti-pyretic effect
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16
Q

What is a common error with mild opioid use?

A

-the overestimation of the amount of drug used for pain killer purposes

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17
Q

What are are examples of endogenous opioids?

A
  • endorphins
  • dynophins
  • encephalins
  • nociceptins

these bind to your opioid receptors and help to explain the benefits/evidence of acupuncture.

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18
Q

What is the mechanism of action of opioids?

A
  • bind to opioid receptors which are widespread around the CNS
  • highest concentration of receptors is in the pons and pain modulation pathways
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19
Q

What are the 3 subtypes of opioid receptors?

A
  • mu
  • delta
  • kappa

these are distributed differently in different tissues and have different physiological effects in the body.

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20
Q

What is the mu opioid receptor?

A
  • mainly located in brain, spinal cord
  • causes analgesia, respiratory depression, euphoria, addiction
  • blocks all pain messages
21
Q

What is the kappa opioid receptor?

A
  • found in brain and spinal cord
  • causes analgesia, sedation,
  • blocks all non thermal pain messages
22
Q

What is the delta opioid receptor?

A
  • found in the brain

- causes analgesia, anti-depression, dependence

23
Q

Which opioid receptor should be activated/targeted in order to manage pain but reduce the risk of addiction?

A

kappa receptor

24
Q

Which opiod receptor should be used to avoid side effects like respiratory depression?

A

mu receptor

25
Q

What does morphine bind to?

A

-binds strongly to mu, but in kappa receptors are still the safest for analgesia

26
Q

What happens when opioid receptor mu is bound?

A
  • potassium channels open
  • membrane hyperpolarises
  • action potential pain is not sent
  • reduces neurotransmitter release
  • signal
27
Q

What happens when opioid receptor kappa is bound?

A
  • closes calcium channels
  • decreases calcium entry
  • reduces neurotransmitter release
  • pain message is not sent
28
Q

Why is kappa the preferred opioid receptor to target?

A
  • has lowered risk of dependence/addiction
  • no respiratory depression
  • reduced effect on reduction of GI motility
29
Q

What are pure opiates?

A
  • drugs directly extracted from opium plant without modification
  • e.g. morphine, thebaine, phenanthrenes,
  • these have a 4 ring structure
30
Q

What are semisynthetic opiods?

A
  • codeine
  • modified phenanthrenes
  • etorphine
  • oxycodone
  • naloxone
  • buprenorphine
31
Q

What are synthetic opiates?

A
  • pentazocine
  • pethidine
  • fentanyl
  • alfentanil
  • refmifentanil
  • methadone
32
Q

What are the reasons for synthetic opiods?

A
  • can increase potency and decrease side effects

- easier to isolate

33
Q

What is naloxone for?

A

it is an antagonist at opioid receptors and is used to treat opiate overdose

34
Q

What are the main uses for opioid drugs?

A
  • analgesia (acute and chronic pain)
  • induce general anaesthetic
  • co induction of general anaesthesia
  • palliative care
  • antitussive (cough suppressant)
35
Q

What are the three common agonists of mu receptors?

A

morphine, alfentanil, remifentanil

36
Q

How do the three agonists of mu receptors differ ?

A
  • their onset of action is different.
  • morphine is the slowest and alfentanil is the fastest
  • their duration of action is also different.
  • morphine lasts the longest while remifentail lasts the shortest
  • they are used for different purposes
  • remifentanil can be used as a controlled release drug
37
Q

What are the side effects of opioids?

A
  • the different receptors on different organs will have different effects
  • some side effects include respiratory depression, constipation, nausea, sedation
38
Q

What is causes tolerance of opioids?

A
  • mechanism uncertain but involves uncoupling of receptors from the G protein system
  • could also be due to down regulation of receptors and the upregulation of adenylate cyclase
39
Q

Why do some opioid drugs cause dependence?

A
  • depdence occurs when the upregulation of adenylate cylase is suddenly opposed.
  • the excessive production of cAMP will cause withdrawal symptoms
40
Q

What are the two main analogues of morphine?

A

codeine and heroin

41
Q

What is codeine?

A
  • use for moderate pain
  • in cough formulations as an antitussive
  • also used to treat diarrhoea
  • 30-60mg enough for painrelief
  • 15-30mg enough for cough suppressant
42
Q

What is heroin?

A
  • analogue of morphine with activity 2x that of morphine
  • has medicinal purposes (terminal patients)
  • polar groups in heroin are hidden so it crosses the bbb much more easily
  • side effects include euphoria, addiction,m tolerance
43
Q

How does heroin cause euphoria?

A
  • when it crosses the bbb, it activates and releases morphine
  • morphine binds to the delta receptor and inhibits the effect and production of GABA
  • Dopamine and its effects are no longer inhibited
  • there is more dopamine released causing euphoria
44
Q

What are the withdrawal symptoms of heroin?

A
  • different between patients
  • drug seeking behaviour
  • lacrimation
  • rhinorrhea
  • yawning
  • sweating
  • restlessness
  • mydriasis
  • tremors
  • nausea
  • tachycardia
  • cramps/spasms
  • general CNS hyper-excitability
  • potential CV collapse
45
Q

What is tramadol?

A
  • purely synthetic opioid drug
  • has multifunctions:
    1. full mu receptor agonist effect similar to morphine
    2. inhibits reuptake of serotonin and enhances its release in inhibitory descending pathways
  • pretty good pain management effects
  • available in oral and IV (70% bioavailabiltiy)
  • no significant CV or respiratory effects with low tolerance and abuse potential
46
Q

What is paracetamol?

A
  • most commonly used drug in NZ
  • actual mechanism not understood but several hypothesis:
    1. inhibits COX, selective for cox 2 to reduce side effects. has antipyretic effect
    2. increases serotonin in descending pathways
    3. modulation of neurotransmission in pain pathways in dorsal horn
  • can be oral or IV (oral bioavailability is 80%)
  • peak plasma levels after oral dose usually achieved within 30-60minutes
  • oral dose is 20-25mg/kg
  • pretty safe in pregnancy
  • mainly metabolised in liver
47
Q

What is significant about paracetamol toxicity?

A
  • rare but still severe and fatal
  • can cause skin disorders like stevens johnson’s syndrome
  • minimal toxic dose causes liver damage (7.5-10g of paracetamol - about 20 tablets)
  • for children this is 150-200mg/kg
  • often seen in suicide attempts
48
Q

What are the 3 different stages of toxicity responses to paracetamol toxicity?

A
  1. nausea/vomiting and malaise
  2. upper right quadrant abdominal pain, nausea, vomiting, tachycardia, hypotension
  3. hepatic necrosis and dysfunction, kidney dysfunction

Medsci305 (17 decks)

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