anaesthesia 5- analgesics

Question 0

what is analgesia?

Answer 0

absence of pain in presence of stimuli which is normally painful.

Question 1

pain - what is it?

Answer 1

unpleasant /emotional experience associated with actual/potential tissue damage.

Question 2

what are the neural mechanisms of pain?

Answer 2

1. unmyelinated slow (c fibres) and myelinated fast (ad fibre)
2. nociceptive cell bodies (dorsal root ganglia)
3. pain fibres terminate in superficial dorsal horn of spinal cord - perception of pain.
4. spinothalamic tract - thalamus.

Question 3

modulation of pain depends on?

Answer 3

thansmission depends on control at the dorsal horn, spinal cord and brain.

Question 4

what is the down -regulation of pain?

Answer 4

temporary suppression of pain transmission eg. to facilitate fight or flight. (adrenaline and endogenous hormone - blocked)

Question 5

what is the up-regulation of pain?

Answer 5

it enhances the pain transmission and ensures protection of injured tissue - avoid in surgery as can result inchronic pain (eeven in the absence of the stimulus!)

Question 6

where in the brain is the nociceptive info modulated? inhibition at? which receptors are located here?

Answer 6

at the dorsal horn, substantia gelatinosa. can be inhibited by ‘descending inhibatiry neurones) eg. PAG - periaqueductal grey in midbrain. and also SG substantia gelatinosa. both have opioid receptors!!!…..this is the predominant site of effects of the analgesics!!!

Question 7

what is hyperallgesia?

Answer 7

increased pain associated with mild noxious stimuli.

Question 8

what is allodynia?

Answer 8

pain produced by non-noxious stimuli eg. normal touch.

Question 9

what are the pharmacodynamics of analgesics? act at?

Answer 9

act at the site of injury and alter nerve conduction. they modify transmission in the dorsal horn. effect the emotional component and the central component.

Question 10

what are the 6 groups of analgesics?

Answer 10

1. opioids
2. nsaids
3. local anaesthetics
4. NMDA agonists
5. alpha 2 agonists
6. others

Question 11

what is a mjor example of an opioid? synthetics of this?

Answer 11

morphine!!!! it is not endogenous. but it is natural. synthetics of this eg. heroin, phenylpiperidine (fentanyl)

Question 12

pharmacokinetics of opioids?

Answer 12

metabolism - first pass with PO (in liver 1st)
half life - 3-6 hours
conjugated in liver
metabolist of morphine is active.

elinination - excreted in urine. hydrolysed in gut and morphine reabsorbed.

Question 13

what is an unwanted side effect of opioids?

Answer 13

sedation, resp depression, negative in heart, emesis, dysphoria, histamine release.

Question 14

opioid receptors? what kind of receptor? effect on camp? most receptors are where?

Answer 14

GPCR. inhibit camp. promote opening of k+ channels (more negaitve cell) inhibit ca channels and so blocks transmission.
mostly on supraspinal/spine.

Question 15

pharmacodynamics of opioids?

Answer 15

reduced neuronal esxcitability. (hyperpolarise)
reduced transmitter release
receptor and brain and spinal cord.
inhibits nociception and impulses and inhibits substance p.

Question 16

pharmacological effects of opioids? PNS effects?

Answer 16

alangesia, sedation, supress cough, supress resp centre. reduce gi motility, histamine release. supress vomiting, constrict pupil.

Question 17

give examples of full mu agonists? (receptor)

Answer 17

morphine, pehtidine, fentanyl, methadone

Question 18

pethidine has no effect on? compared to toher full agonists?

Answer 18

heart!

Question 19

morphine? schedule? metabolised to? causes emesis? side effects?

Answer 19

schedule 2 controlled drug. metabolised to morphine-6-glucuronidide.
causes emesis (vomit)
negative on heart and resp
reduces gi motility.

Question 20

pethidine? type of? why not use it i/v?

Answer 20

full mu agonist. shcedule 2 controlled drug. licensed for vet use.
spasmolitic, positive on heart, cause histamine release if given iv. must use im!!

Question 21

fentanyl? used for (duragesic?) shedule? onset? patches? or iv

Answer 21

supress mild-chronic pain. schedule 2 controlled drug. rapid onset, used in patches or i/v. rescue analgesic.

Question 22

methadone? type of? schedule? used for? which side effect is avoided?

Answer 22

full mu agonist. opioid. shcedule 2 but unlicensed. used for moderate pain. no emesis.

Question 23

partial mu agonists?eg?

Answer 23

buprenorphine

butorphanol.

Question 24

buprebnorphine - what type of drug? shcedule? used for?

Answer 24

partial mu agonist. schedule 3 controlled drug. partial mu agonist/antagonist
moderate pain
used for partail reversal of full mu agonist.

Question 25

butorphanol? type of drug? POM? anti-tussive?

Answer 25

patrtial mu agonist. POM - prescription only medicine.

licensed. mild pain . potent anti-tussive (coughing.)

Question 26

what is neuroleptanalgesia? 3 eg’s? hypnorm?? immobilon?

Answer 26

drug combinations used. semiconcious. eg. hypnorm - fentanyl and fluanisone.
large animal imobilon - etorphine and ACP.
small animal immobilon - etorphine and methotrimeprazine.