GI Drugs Flashcards
PPIs- PKs?
Omeprazole is a prodrug activated by stomach acid!
PPIs- ADRs?
GI disturbance, headache, rash, osteoporosis
PPIs- DDIs?
CYP inhibitor- increase MTX, decrease clopidogrel (reduced activation by CYP!)
H2 antagonists- mechanism?
Antagonise H2 receptors -> decrease acid secretion, acts immediately and has short half life so take 2 x day
H2 antagonists- ADRs?
GI disturbance, headache, gynaecomastia, hypotension
H2 antagonists- DDIs?
Cimetidine is CYP inhibitor- increase AEDs, aminophylline, decrease clopidogrel
PPIs- mechanism?
Inhibit H+/K+ ATPase (omeprazole IRREVERSIBLY inhibits!) -> decrease acid secretion! Takes days to have full effect (take out all pumps!)
Domperidone- mechanism?
Dopamine (D2) antagonist -> inhibits vomiting response from trigger centre in 4th ventricle (postrema) ALSO increase rate of stomach emptying
Domperidone- uses?
Acute N&V esp in parkinsons (caused by L-dopa)
Ondansteron -mechanism?
Serotonin antagonist -> Inhibits postrema in 4th ventricle, inhibits vagal vomiting signals from GI tract
Domperidone- ADRs?
Increased prolactin-> galactorrhoea, dystonia
Ondansteron - uses?
Iatrogenic vomiting- chemotherapy and post op nausea
Ondansteron- ADRs
Headache, constipation, flushing
Hyoscine - mechanism?
ACh antagonist in vestibular apparatus -> stops MOTION SICKNESS
Hyoscine ADRs
Anti-cholinergic effects plus bradycardia (unexpected!!)
Cyclizine- mechanism?
Histamine (H1) antagonist -> inhibits vomiting centre in medulla and vestibular apparatus
Cyclizine- uses?
Acute N&V
Cyclizine- ADRs
Long QT, sedation
Metoclopramide- mechanism?
D2 antagonist, anti-cholinergic AND serotonin antagonist
Metoclopramide- uses?
GI causes of N&V, migraine, post op nausea
Metoclopramide- ADRs
Galactorrhoea, dystonia, extra pyramidal signs (avoid in parkinsons)
Drugs for hard faeces constipation?
Bulk forming, faecal softeners, osmotic laxatives
Soft faeces constipation?
Stimulant laxatives e.g. Senna
Bulk forming laxatives mechanism?
E.g isphaghula, indigestible vegetable fibre!! (Yum)
When don’t use bulk laxatives?
Ulceration/adhesions -> obstruction!!
Faecal softeners- example, mechanism, uses?
E.g. Arachis oil, glycerol -> lubricate and soften stool, use in adhesions (no obstruction risk!), haemorrhoids and anal fissures
Osmotic laxatives- Mg/Na salts mechanism, example, uses?
E.g. Phosphate enema -> Increase water retention -> increase peristalsis, quick acting! Use in resistant constipation for urgent relief!!
Osmotic laxatives - lactulose mechanism, uses?
Galactose and fructose, bacteria FERMENT it -> acetic and latic acid -> osmotic effect, use in LIVER FAILURE (decreased ammonia)
Stimulant laxatives- example, mechanism?
Senna -> excite sensory nerves -> increase water and electrolyte retention -> increase peristalsis!
Stimulant laxatives- ADRs and contra indications
Abdo cramps, colonic atony, hypokalaemia DONT use in OBSTRUCTION
Anti motility drugs- example, mechanism?
Loperamide (opiate analogue) -> opioid receptors in bowel -> decrease motility, increase time for water and salt resorption, increase anal tone, decrease defecation reflex
Loperamide- indications and contraindications
Use in chronic diarrhoea NOT in IBD as -> toxic megacolon
Anti-spasmodics- example, mechanism, uses?
Meberavine, anti-muscarinic-> decrease spasms and painful cramps, maintain motility, use with bulk forming agent to treat IBS!
