pharmacology of pain Flashcards
what are the main drugs used for pain?
Paracetamol
opioids:
Weak – codeine, tramadol
Strong – morphine, fentanyl, (heroin)
co-amoxiclav
lactulose
what is the mechanism of action of paracetamol?
Still not totally clear.
At peripheral sites, may inhibit a peroxidase enzyme which is involved in the conversion of arachidonic acid to prostaglandins (1st step in this pathway involves the enzyme, cyclooxygenase). The ability of paracetamol to inhibit peroxidase can be blocked if excessive levels of peroxide build up (as is commonly seen in inflammation)
Activation of descending serotonergic pathways possibly via 5HT3 receptor activation.
Inhibits reuptake of endogenous endocannabinoids, which would increase activation of cannabinoid receptors - this may contribute to activation of descending pathways.
what is the drug target of paracetamol?
Unclear.
5HT3 receptors/Cannabinoid reuptake proteins/Peroxidase
what are the side effects of paracetamol?
Relatively safe drug with few common side effects.
OVERDOSE:
Liver damage and less frequently renal damage.
Nausea and vomiting early features of poisoning (settle in 24h).
Onset of right subcostal pain after 24hindicates hepatic necrosis.
what are some facts about paracetamol?
Analgesic and anti-pyretic.
Does NOT possess anti-inflammatory activity.
A number of medications contain paracetamol, so care must be taken to avoid accidental overdose. Legal restrictions on sales of paracetamol have significantly reduced the number of fatalities from overdose in the UK although, regrettably, ingestion of large amounts of paracetamol remains a common method of suicide.
In 2020, paracetamol was the 14th most commonly prescribed drug in the West London area.
Probably the most commonly prescribed over the counter (OTC) medicine in the world.
what is the mechanism of action of 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.
Anti-tussive effect due to decreased activation of afferent nerves relaying cough stimulus from airways to brain
what is the drug target of opioids?
Opioid receptor
what are the side effects of opioids?
Mild – nausea & vomiting (increase activity in chemoreceptor trigger zone) and constipation (opioid receptors in GIT can reduce gut motility)
OVERDOSE - respiratory depression (direct and indirect inhibition of respiratory control centre.)
what are some facts about opioids?
Prescriptions for opioids in the UK have more than doubled in the last 20 years.
In 2020, several ‘weak’ opioids or weak opioid/paracetamol combinations were among the most commonly prescribed drugs in the West London area.
Co-codamol (paracetamol + codeine) = 26th
Co-dydramol (paracetamol + dihydrocodeine) = 60th
Tramadol = 69th
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 drug target of 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.
what are some facts about co-amoxiclav?
Amoxicillin is a semisynthetic antibiotic with a broad spectrum of bactericidal activity against many gram-positive and gram-negative microorganisms
Hypersensitivity to penicillins is relatively common. Usually associated with rash but can lead to anaphylactic reactions.
Co-amoxiclav is a commonly prescribed antibiotic in hospital settings.
what is the mechanism of action of lactulose?
Lactulose 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 drug target of lactulose?
No drug target
