Analgesic agents Flashcards
What are the three types of pain and what are opioids used for?
Nociceptive (tissue damage)
Inflammatory
Neuropathic pain
Opioids for nociceptive and inflammatory
How do opioids work?
Bind to their receptor in the presynaptic neuron, reduces the function of the Ca2+ channel.
It also binds to receptors in the postsynaptic neuron to increase the conducation of the K+ channel resulting in hyerpolarisation.
What are agonists, antagonists, agonist-antagonists and partial agonists of the opioid receptors?
Agonists: morphine, fentanyl, pethadine
Antagonists: naloxone, naltrexone
Agonist-antagonist (depending on the receptor): Nalorphine, pentazocine
Partial agonist: buprenorphine
What are the adverse effects of opioids?
Respiratory depression, nausea nad vomiting, drowsiness, constipation, itching, ilius, hypotension, bradycardia
Caution with COPD, sleep apnoea, elderly
What do you do for someone who is addicted?
Give methadone or buprenorphine,
Give clonidine to reduce the autonomic symptoms of withdrawal.
Give anti-diarrhea and anti-nausea/vomiting, and something for muscle cramps
OR do rapid detoxification, when patient is under general give lots of naltrexone.
What are the features of morphine?
Powerful analgesia, sedation, Cough suppression, miosis altered mood (euphoria and tranquility) Large volume of distribution Half-life of 3 hours.
Side effects: respiratory depression, nausea adn vomiting, constipation, addiction, pruritus, bradycardia, hypotension, biliary colic
IV, IM, oral
Oral bioavailability (25%)
Metabolised in the liver - some biproducts have analgesic effects.
What are the features of pethadine?
It is synthetic, less miosis, less biliary spasm
Causes dry mouth and tachycardia
Oral bioabailability 50%
Highly lipid soluble - fast onset.
IV and oral
Same side effects as other opioids.
One byproduct of metabolisim is a problem for patients with renal failure because it will accumulate.
Interacts with monoamine oxidase inhibitors (MAOI)
What are the features of fentanyl?
High lipid solubility (fast onset)
80-100 times more potent than morphine
IV, IM, transmucosal lozenges, nasal and sublingual spray, sublingual tablets, transdermal patches - but this is slow and cant rapidly change doses.
Transdermal iontophoresis - trnsdermal administration of ionizable drugs. Electrically cgarged components are propelled through the skin by an external electric field - patient has some control.
What are the features of methadone?
Fully synthetic
Well absorbed from all roues - oral (70%), rectal, subcutaneous, IV, sublingual,
Rapid onset of analgesia (30-60 mins)
No cognitive impairment or euphoria, safe in liver and renal failure.
Used for chronic pain, neuopathic pain (better than the others)
For opioid withdrawal or detox.
What are the features of tramadol?
Synthetic
Oral (70%)
Not strrong
Inhibit uptake of noradrenaline and serotonic,
Causes the release of endogenous opioids.
Side effects N and V
May cause serotonin syndrome (careful with antidepressants)
little respiratory depression, caution with epilepsy patients.
What are the features of codine?
Opiate
Mild to moderate pain,
Suppresses cough, anti-diarrhoeal
Drowsiness and constipation
Can cause dependence
Codeine is metabolised to morphine - ultra-rapid metabolisers are at a higher risk of toxic opioid effects and slow metabolisers may not receive adequate effects
What are coanalgesics and some examples?
adjuvant drugs whose primary purpose is not for pain relief by they can enhance the function of analgesics.
Tricyclic antidepressants, anticonvulsants, corticosteroids, clonidine
What is the other name for aspirin?
acetyl salicylic acid
What is the mechanism of action of NSAIDs?
They inhibit the cyclooxygenase enzymes, leading to suppression of prostanoids production in cells.
Newer agents only inhibit COX2.
This process is reversible for all drugs except for aspirin,
What do NSAIDs do?
Decrease inflammation by decreasing prostaglandins.
Reduce mild pain by decreasing by decreasing prostaglandins.
Anti-pyretic by decreasing PGE2
Anticoagulation by decreasing thromboxane A2 in platelets.