Pharmacology of Pain Flashcards
What are some weak opioids?
codeine, tramadol
What are some strong opioids?
morphine, fentanyl, (heroin)
What is the mechanism of action for opioids?
Over-arching mechanism at a cellular level is a depressant effect on cellular activity. Multiple sites within pain pathway, where activation of the opioid receptor leads to decreased perception or increased tolerance to pain.
Why is there an Anti-tussive effect to opioids?
Anti-tussive effect due to decreased activation of afferent nerves relaying cough stimulus from airways to brain
What is the primary target for Opioids?
opioid receptor
What are the mild side effects of opioids?
nausea & vomiting (increase activity in chemoreceptor trigger zone) and constipation (opioid receptors in GIT can reduce gut motility)
What are the symptoms of opioid overdose?
respiratory depression (direct and indirect inhibition of respiratory control centre.)
What is the mechanism of action of Co-amoxiclav?
Amoxicillin (like all penicillin like drugs) binds to bacterial penicillin binding proteins. This prevents transpeptidation (the cross linking process for bacterial cell wall synthesis)
Clavulanate is an inhibitor of beta lactamase. Beta lactamase is a bacterial enzyme that can degrade beta lactam anti-biotics and thus confer resistance to these anti-biotics.
What is the primary target site for Co-amoxiclav?
Amoxicillin = penicillin binding proteins
Clavulanate = beta lactamase
What are the side effects of Co-amoxiclav?
Amoxicillin is well tolerated. Most common side effects are nausea and diarrhoea.
Describe Amoxicillin
Amoxicillin is a semisynthetic antibiotic with a broad spectrum of bactericidal activity against many gram-positive and gram-negative microorganisms
What happens in hypersensitivity to penicillin?
Hypersensitivity to penicillins is relatively common. Usually associated with rash but can lead to anaphylactic reactions.
Where is Co-amoxiclav commonly prescribed?
hospital settings
What is the mechanism of action of Lactulose?
actulose is a non-absorbable disaccharide. It reaches the large bowel unchanged. This causes water retention via osmosis and an easier to pass stool. It can also be metabolised by colonic bacteria. The colonic metabolism of sugars has an additional laxative effect.
What is the primary target of Lactulose?
No drug target
What are the side effects of Lactulose?
Abdominal pain, diarrhoea, flatulence, nausea.
How quickly does Lactulose begin working?
Begins working within 8-12 hours but may take up to 2 days to improve constipation.
What is Lactulose’s effect on constipation?
Constipation is a very common side effect of opioids. Lactulose is often prescribed prior to commencement of opioid therapy to improve symptoms associated with constipation.
What is given for mild pain?
Nonopioid +/- adjuvant therapy
What is given for mild to moderate pain?
weak opioid +/- nonopioid +/- adjuvant therapy
What is given for moderate to severe pain?
Strong opioid +/- nonopijoid therapy +/- adjuvant therapy
What determines a drugs ability to get to the brain?
Lipid solubility as the major route for drug permeation to the brain is via passive diffusion
What is the effect of opioids at the pre-synaptic neurone?
inhibit ATP to cAMP conversion
inhibit calcium influx
enhance potassium reflux
What are the effects of morphine and naloxone on opioid receptors?
Morphine is an opioid receptor agonist. Naloxone is an opioid receptor antagonist. Agonists possess affinity and efficacy for a receptor. Antagonists only possess affinity for a receptor.
What is the relationship between morphine and codeine?
codeine is primarily a pro-drug for morphine. As you can see in the figure below, codeine can be metabolized to both norcodeine (inactive metabolite) AND morphine (active metabolite). In the liver, cytochrome P450 enzymes are responsible for this metabolism. CYP3A4 is responsible for ‘fast’ metabolism of codeine to norcodeine and CYP2A6 is responsible for ‘slow’ metabolism of codeine to morphine
