Analgesics (year 2) Flashcards
what are analgesics used for?
to manage pain
what is acute pain generally associated with?
tissue damage
animals rapidly alter behaviour when they have acute pain, why?
minimise damage and optimise healing conditions
describe chronic pain
persistent pain with no biological purpose of end point
what is the acronym used to remember the analgesics?
NO PLAN
what are the drugs used to manage acute pain?
NSAIDs Opioids Paracetamol Local anaesthetics Alpha2 agonists NMDA antagonists
what is the mode of action of NSAIDs?
they are COX inhibitors
what are the three effects of NSAIDs?
analgesia
anti-inflammatory
anti-pyrexia
what are the side effects of NSAIDs?
GI - vomiting, diarrhoea, ulcers
renal - alter blood flow
liver - idiosyncratic
clotting
give an example of an NSAID
meloxicam
what is the mechanism of action of opioids?
receptors throughout body but we target the dorsal horn of the spinal cord to reduce the action of excretory neurotransmitters in nociceptors
what are the three opioid receptors?
mu, kappa, delta
what are the different opioid receptors targeted for?
mu - analgesia
kappa - sedation, some analgesia
what are the three drug types that target opioid receptors?
full mu agonist
partial mu agonist
mu antagonist kappa agonist
what are some examples of full mu agonists?
morphine, methadone, pethidine, fentanyl
name a partial mu agonist
buprenorphine
why is buprenorphine (a partial mu agonist) used?
last longer fewer side effects lower schedule (less paper work)
name an opioid agonist-antagonist used in veterinary
butorphanol
why might butorphanol be used?
if you want sedation but don’t require analgesia
what are the effects of opioids?
analgesia and sedation
name some side effects of using opioids
bradycardia respiratory depression reduced GI motility excitment dysphoria euphoria vomiting
opioids have an antagonists available for the mu receptors, what is it called?
naloxone
how is paracetamol administered?
orally or IV
what are the effects of paracetamol?
analgesia and anti-pyrexia
what species should paracetamol not be used in?
cats - metabolise it to a toxic metabolite that damages RBCs
what are the side effects of paracetamol use?
hepatotoxicity
hypotension (IV administration)
name the two classes of local anaesthetic drugs
amides and esters
what are some examples of amides used as local anaesthetics?
lidocaine, bupivacaine, mepivacaine
where are amides metabolised?
liver
give an example of an ester used as a local anaesthetic
procaine
what is the mechanism of action of local anaesthetics?
act on sodium channels to prevent propagation of action potentials
are esters or amides longer acting local anaesthetics?
amides as they require metabolisation from the liver not just any tissue
what are the effects of local anaesthetics?
analgesia, anti-inflammatory, anti-arrhythmic
what are the some general features of local anaesthetics?
higher pKa means more ionising so the slower the onset of action
more lipid soluble the faster the onset
greater protein binding means longer duration of action
the more vasodilation it causes the shorter the duration of action
what are the side effects of local anaesthetics?
loss of autonomic tone
loss of motor activity
CNS toxicity
cardiac toxicity
alpha2 agonists are synergistic with which other analgesic group?
opioids
what is the mechanism of action NMDA antagonists?
block NMDA receptors involved in the pain pathway in the CNS
name an NMDA antagonist used for acute pain management
ketamine
what are the effects of ketamine?
analgesia and anaesthesia
what are the side effects if NMDA antagonists?
excitement, hypertonicity, myocardial depression, sympathetic stimulation
name some drugs used to manage chronic pain
gabapentin
amantadine
antidepressants
capsacin
what questions do we ask when choosing an analgesic?
What type of pain is expected?
What degree of pain is expected, or already present?
Which drugs are available?
How easy is a certain drug to administer to that individual?
Is the drug licensed in the species?
Is it safe to use?
