Analgesic Drugs Flashcards
Describe the WHO Pain ladder
- Strong opioid
- Weak opioid
- NSAIDs
- Paracetamol
What is the difference between an opiate and opioid?
Opiate - substances extracted from opium
Opioid - any agent that acts on opioid receptors (including endogenous peptides)
What descending pathway acts to modify pain?
Supraspinal antinociception
Describe the supraspinal antinociception pathway
Peri-aqueductual grey matter sends signals to the locus ceruleus and nucleus raphe magnus which project to dorsal horn of spinal cord and inhibit nociceptive transmission
What stimulates the peri-aqueductal grey matter?
Opioids and electrical stimulation
Where is the PAG?
Midbrain
Where is the locus ceruleus?
Pons
Where is the nucleus raphe magnus?
Medulla
What does the PAG excite?
Nucleus raphe magnus
Locus coruleus
What is the effect of PAG excitation of NRM and LC?
They excite 5HT and NA neurones which project to the dorsal horn and inhibit nociceptive transmission
Describe the cellular action of opioids
Inhibit opening of voltage activated calcium channels to prevent release of neurotransmitter
Opens potassium channels to suppress excitation
Inhibits adenylate cyclase
Name the three opioid receptors
MU
Delta
Kappa
What is the effect of opioids on the respiratory system?
Apnoea - blinding of medullary resp centre to carbon dioxide
What is the effect of opioids on the cardiovascular system?
Orthostatic hypertension - reduced sympathetic tone and bradycardia - histamine evoked vasodilation
What is the effect of opioids on the GI system?
Nausea, vomiting, constipation, intrabilary pressure
What is the effect of opioids on the CNS?
Confusion, euphoria, dysphoria, hallucinations, dizziness, hyperalgesia
What can morphine cause in asthmatics?
Degranulation and bronchospasm
How do most analgesic drugs work?
Prolonged activation of opioid receptors
Name opioid agonists
Morphine Diamorphine Coedine Fentanyl Pethidine Buprenophine Tramadol Methadone
Name an opioid antagonist
Naloxone
When is morphine used?
Severe acute pain
Chronic pain
Where is morphine broken down?
Liver
- M3G (inactive)
- M6G (analgesic activity)
Name the methods of administration of morphine
IV
IM, SC, oral
Epidural or intrathecal
What is another name for diamorphine?
Heroin
How is diamorphine different to morphine?
More lipophilic and has a rapid onset of action when administered IV as can enter CNS
When is codeine used?
Mild/moderate pain - hepatic metabolism to morphine
What are the higher potency derivatives of codeine?
Oxycodone and hydrocodone
In addition to pain relief what are the other effects of codeine?
Anti-diarrhoeal
Anti-tussive
Describe fentanyl
75-100 times more potent than morphine
Given IV to provide analgesia in anaesthetic
Transdermal, IV or sublingual delivery
When is pethidine used?
Acute pain in labour
Rapid onset
What drug can pethidine not be used with?
Monoamine oxidase inhibitors
When is buprenorphine used?
Chronic pain with patient controlled injection systems
What is the mechanism of action of tramadol?
Weak mu receptor agonist potentiates the descending pathways
What disease should tramadol be avoided in?
Epilepsy
Where does methadone work?
Weak mu receptor agonist
Acts on potassium channels
NMDA glutamate receptors
5HT receptors
What can methadone be used for?
Terminal cancer
Withdrawal
What does naloxone do?
Competitive antagonist of mu receptors and used to reverse opioid toxicity
Where do non-selective NSAIDs work?
COX 1 inhibitor
Where do selective NSAIDs work?
COX2 induced locally at sites of inflammation
Name non-selective NSAIDs
Aspirin
Ibuprofen
Diclofenac
Naproxen
Name selective NSAIDs
Etoricoxib
Celecoxib
Inmiracoxib
Name drugs that can be used in neuropathic pain
Gabapentin
Pregablin
Amitriptyline
Carbamazepine
How do gabapentin and pregablin work?
Reduce cell surface expression of a subunit of voltage gated calcium channels which are unregulated in damaged neurones
What can gabapentin and pregablin be used for?
Pregablin - diabetic neuropathy
Gabapentin - migraine
How does amitriptyline work?
Decrease reuptake of noradrenaline
Name a sodium channel blocker
Carbamazepine
What type of pain can carbamazepine be used for?
Trigeminal neuralgia