9.1 Opioids Flashcards
describe the 2 dimensions of pain
- sensory dimension
-what it feels like, where it is - affective dimension
-emotional, upsetting side
-projects to limbic system
where’s the pain gate, and what does it include?
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
2 main types of pain fibres
a delta: fast, sharp pain
c: slow pain (unmyelinated)
both are primary sensory neurones
receptor type that opioids act on
mu
neurotransmitters of descending pathways from brain to pain gate
noradrenaline
5-ht (serotonin)
neurotransmitters of inhibitory inteneurones to pain gate
GABA
enkephalins
link depression to pain
weighted perception of pain due to a deficiency in serotonin so less inhibition of pain gate via descending pathways from brain
3 locations of pathways which link to descending pathways of brain
common pathway
- insular cortex: taste
- amygdala: fear, stress, anxiety
- hypothalamus: menstrual cycle
from origin to periaqueductal grey to rostral ventral medulla to spinal cord
which type of G protein are endogenous opioid peptides
G alpha i
name some therapeutic opioids
codeine
buprenorphine
diamorphine
fentanyl
morphine
tramadol
effects of opioids
analgesia
antitussive
anaesthetic
anti diarrhoea
palliation
how is codeine converted to morphine
prodrug metabolised by CYP2D6
ADRs
constipation
drowsiness
euphoria (dopamine)
mitosis
nausea
respiratory depression
contraindications for opioids
comatose
raised ICP
respiratory depression
paralytic ileus (slows GI)
asthmatics (histamine release by morphine)
DDIs for opioids
AEDs, benzodiazepines: CNS depression
other opioids
opioids used for opioid use disorder
buprenorphine
methadone
opioid used for overdose. how does it work?
naloxone
competitive opioid receptor antagonist, rapid distribution
why might naloxone need to be administered subsequent times in respiratory depression emergency?
short half life so may leave some opioid still there which could cause respiratory depression again
signs of opioid overdose
mitosis
cyanosis
slow HR, weak pulse, low BP
slow, irregular breathing
non responsive
why could opioid use disorder develop?
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
how does opioid withdrawal present?
excess of normal neuronal activity
-insomnia
-anxiety
-excess sweating
-enlarged pupils
-tachypnoea
how do opioids produce their analgesic effect?
act on mu receptors, decrease cAMP signalling so inhibit nociceptive transmitters
