9. Drugs for Pain Flashcards
What is the difference between A and C pain fibres?
A is fast, sharp pain
C is slow, dull ache
What are the endogenous opioids?
Endorphins
Enkephalins
Dynorphins
What receptors do endorphins bind to?
Mu
What receptors do enkephalins bind to?
Delta and mu
What are the types of enkephalins?
Met-
Leu-
What receptors do dynorphins bind to?
Kappa
What are the types of dynorphins?
A and B
What kind of receptors are opioid receptors?
GPCRs
What is the MOA of opiates?
Bind to GPCR and inhibit adenylate cyclase to reduce cAMP> close Ca++ channels or open K+ channels> reduced NT release
What are the inhibitory neurotransmitters?
GABA (brain)
Glycine (peripheral)
What type of drug is morphine?
Strong opioid agonist
What are the effects of morphine?
Increase pain threshold without loss of consciousness
Euphoria at M or dysphoria at k
What are the adverse effects of opiates?
Respiratory depression, sedation
Pinpoint pupils in overdose
Nausea, vomiting, constipation
Tolerance, dependence
What is methadone used for?
Treatment of opiate addiction
What increases the efficacy of fentanyl compared to morphine?
Has a higher lipophilicity so it can cross the BBB much more rapidly
What non-analgesic effect does codeine have?
Antitussal
Name an analogue of codeine
Tramadol
What is the active metabolite of tramadol?
What is its other effects?
Dematralodol
Inhibits reuptake of NA and serotonin
What adverse effects are associated with tramadol?
Increased risk of seizures, serotonin syndrome and dependence
Name 2 opioid antagonists
Naloxone
Naltrexone
What are the functions of opioid antagonists?
Naloxone in overdoses
Naltrexone in withdrawal
What kind of drug is buprenorphine?
Mixed agonist; also has antagonist properties
Why is buprenorphine used?
In withdrawal it reduces high that other opiates would give
Less euphoria, sedation, milder withdrawal
Which opiate properties is tolerance developed to?
Analgesia
Euphoria
Respiratory depression
Emesis
What opiate properties is tolerance not developed to?
Pupillary constriction
Constipation
What is neuropathic pain?
Due to nerve damage caused by toxins, infections, autoimmunity or tumours
Numbness along path of nerve, burning or heavy sensation
Anticonvulsants and antidepressants used to treat
What is the MOA of anticonvulsants?
Inactivate Na+ channel to reduce neuronal excitability
Gapabentin acts on Ca++ channels
Name 3 anticonvulsants that act on Na+ channels
Carbamazepine
Lamotrigine
Phenytoin
What is the MOA of antidepressants?
Monoamine reuptake inhibitors
Name 2 topical anaesthetics
Lidocaine
Benzocaine
How do topical anaesthetics work?
Block Na+ preventing APs
How is systemic toxicity from an injected anaesthetic avoided?
Co-administer a vasoconstrictor to avoid seeping into vessels
eg. adrenaline
Name 2 general anaesthetics that target GABA channels
Barbituates and benzodiazepines
What channel does ketamine block?
NMDA (glutamate)
What is the limitation of halothane as an inhaled anaesthetic?
Must be given with oxygen
What is the limitation of desflurane?
Rapidly excreted
What channel does nitrous oxide block?
NMDA
What used to be used to describe the efficacy of inhaled anaesthetics?
Blood: gas partition coefficient
Blood: brain partition coefficient
What is now used to calculate the potency of inhaled anaesthetics?
Minimum alveolar concentration
What is the minimum alveolar concentration?
Volume of anaesthetic in inspired air that provides analgesia to 50% of population
