9.1 Opioids

Question 1

describe the 2 dimensions of pain

Answer 1

1. sensory dimension
   -what it feels like, where it is
2. affective dimension
   -emotional, upsetting side
   -projects to limbic system

Question 2

where’s the pain gate, and what does it include?

Answer 2

In dorsal horn of spinal cord

-pain fibres excitatory to cell body of second order neurone
-descending pathways from brain inhibitory to cell body of second order neurones
-inhibitory interneurones from mechanoreceptors in skin

Question 3

2 main types of pain fibres

Answer 3

a delta: fast, sharp pain

c: slow pain (unmyelinated)

both are primary sensory neurones

Question 4

receptor type that opioids act on

Answer 4

mu

Question 5

neurotransmitters of descending pathways from brain to pain gate

Answer 5

noradrenaline
5-ht (serotonin)

Question 6

neurotransmitters of inhibitory inteneurones to pain gate

Answer 6

GABA
enkephalins

Question 7

link depression to pain

Answer 7

weighted perception of pain due to a deficiency in serotonin so less inhibition of pain gate via descending pathways from brain

Question 8

3 locations of pathways which link to descending pathways of brain

common pathway

Answer 8

1. insular cortex: taste
2. amygdala: fear, stress, anxiety
3. hypothalamus: menstrual cycle

from origin to periaqueductal grey to rostral ventral medulla to spinal cord

Question 9

which type of G protein are endogenous opioid peptides

Answer 9

G alpha i

Question 10

name some therapeutic opioids

Answer 10

codeine
buprenorphine
diamorphine
fentanyl
morphine
tramadol

Question 11

effects of opioids

Answer 11

analgesia
antitussive
anaesthetic
anti diarrhoea
palliation

Question 12

how is codeine converted to morphine

Answer 12

prodrug metabolised by CYP2D6

Question 13

ADRs

Answer 13

constipation
drowsiness
euphoria (dopamine)
mitosis
nausea
respiratory depression

Question 14

contraindications for opioids

Answer 14

comatose
raised ICP
respiratory depression
paralytic ileus (slows GI)
asthmatics (histamine release by morphine)

Question 15

DDIs for opioids

Answer 15

AEDs, benzodiazepines: CNS depression
other opioids

Question 16

opioids used for opioid use disorder

Answer 16

buprenorphine
methadone

Question 17

opioid used for overdose. how does it work?

Answer 17

naloxone

competitive opioid receptor antagonist, rapid distribution

Question 18

why might naloxone need to be administered subsequent times in respiratory depression emergency?

Answer 18

short half life so may leave some opioid still there which could cause respiratory depression again

Question 19

signs of opioid overdose

Answer 19

mitosis
cyanosis
slow HR, weak pulse, low BP
slow, irregular breathing
non responsive

Question 20

why could opioid use disorder develop?

Answer 20

prevent GABA inhibition of mesolimbic pathway, so more dopamine is released which causes pleasure

and in some people, more drug may be needed over time to elicit the same response

Question 21

how does opioid withdrawal present?

Answer 21

excess of normal neuronal activity
-insomnia
-anxiety
-excess sweating
-enlarged pupils
-tachypnoea

Question 22

how do opioids produce their analgesic effect?

Answer 22

act on mu receptors, decrease cAMP signalling so inhibit nociceptive transmitters