git - drugs for constipation and diarrhoea Flashcards
name 7 classes of drugs used for constipation
- bulk-forming laxatives
- stool surfactant agents (softeners)
- osmotic laxatives
- stimulant laxatives
- chloride channel activators
- opioid receptor antagnoists
- serotonin 5-HT4 receptor agonists
name 3 bulk-forming laxatives
- psyllium (plant fibre) - 1st line
- methylcellulose (semi-synthetic)
- polycarbophil (synthetic)
moa of bulk-forming agents
water gets absorbed into fibre mass, forming gel that distends colon (increases stool mass) → promote peristalsis
adverse effects/cautions of bulk-forming agents
- flatus, bloating, abdo pain (due to bacterial digestion of plant fibres)
- affect absorption of other oral drugs → do not use 2h before or after
- administer w lots of water
contraindication for bulk-forming agent
suspected obstruction
name 2 stool surfactant agents
- glycerin + NaCl (enema)
- mineral oil (oral)
moa of stool surfactant agents
- lowers surface tension, allowing water and lipids to penetrate
- ↑ stool mass → promote peristalsis
- ↑ softness of stool mass
- mineral oil lubricates + retards water absorption from stools
adverse effects of mineral oil
- aspiration → lipid pneumonitis (aspiration pneumonia)
- impair absorption of vit ADEK
name 4 osomotic laxatives
- lactulose (non-absorbable sugar)
- magnesium hydroxide/sodium phosphate (non-absorbable salts)
- macrogol (balanced PEG)
moa of osmotic laxatives
- osmotically-mediated water movements into bowel → increase stool liquidity and vol → stimulate peristalsis
adverse effects of lactulose
- severe flatus and abdo cramps
- must administer w lots of water
adverse effects of sodium phosphate
- hyperphosphatemia
- hypernatremia
- hypocalcemia
- hypokalemia
- arrythmia
- acute renal failure
contraindications for osmotic laxatives
- renal insufficiency
- cardiac disease
- frail elderly on diuretics
name 2 stimulant laxatives
- bisacodyl
- senna
moa of stimulant laxatives
produce migrating colonic contractions
use of stimulant laxatives
- LT use in neurologically impaired/bed bound pts
- bisacodyl combined w PEG to clean colon for colonoscopy
adverse effects of stimulant laxatives
- chronic use → dependence and destruction of myenteric plexus → colonic atony and dilation
adverse effects of senna
- brown pigmentation of colon
- possible carcinogenesis
why should milk prdts not be taken w bisacodyl
- cause enteric coating of bisacodyl to break down too fast → risk of gastric irritation → do not take within 1h of consuming milk prdts
only affects oral bisacodyl, can still prescribe rectal
name 1 Cl channel activator
lubiprostone
moa of Cl channel activators
- stimulate type 2 Cl channels
- increases Cl-rich fluid secretions
- stimulates motility and shortens intestinal transit time
used only when pt unresponsive to other laxatives
adverse effects of Cl channel activators
- return of constipation after discontinuation
- nausea
contraindication for Cl channel activators
pregnancy
name 1 opioid receptor antagonist
methylnaltrexone bromide
moa of opioid receptor antagonist
- for opioid-induced constipation
- block of intestinal μ opioid receptor
does not cross BBB, will not block analgesic effect of opioids
adverse effects of opioid receptor antagonists
- common: abdo pain, nausea, diarrhoea, flatulence, sweating
- rare: GI perforation
name 2 5-HT4 agonists
- cisapride
- prucalopride
moa of 5-HT4 agonists
- stimulation of 5-HT4 increases neurotransmitter release and smooth muscle motor activity → prokinetic effect on GI motilty
adverse effects of 5-HT4
- abdo pain, diarrhoea, nausea, dizziness, headache
- cisapride: adverse cardiovascular events (due to action on hERG K+ channel)
contraindication for 5-HT4 agonists
complete intestinal obstruction
name 6 classes of drugs used for diarrhoea
- opioid agonist
- colloidal bismuth cmpds
- intestinal adsorbents
- lactobacillus acidophilus
- bile salt-binding resins
- somatostatin-like peptides
drug classes for acute diarrhoea
- opioid agonists (1st line)
- intestinal adsorbents
- colloidal bismuth cmpds
- lactobacillus acidophilus
drug classes for chronic diarrhoea
- bile salt-binding resins
- somatostatin-like peptides
name 2 opioid agonists
- loperamide
- diphenoxylate + atropine
1st line for rapid relief of diarrhoea!
moa of opioid agonists
act on enteric nervous system → increase colonic transit time
adverse effects of opioid agonists
- at higher dose, diphenoxylate can have CNS effects incl addiction and abuse → LT use can cause dependence
- cardiac abnormalities on overdose of loperamide
loperamide does not cross BBB → no CNS effects
why is atropine added to diphenoxylate
- anticholinergic effects discourage abuse
- contributes to antidiarrhoeal action
moa of bismuth cmpds
- antimicrobial effect and binds enterotoxins
- salicylate (from bismuth subsalicylate) inhibits intestinal prostaglandin prodn and Cl secretion → anti-diarrhoeal effect
adverse effects of bismuth cmpds
- harmless blackening of stool and tongue
- encephalopathy
- use for short periods
- avoid in pts w renal insuff
- salicylate toxicity (w high dose of bismuth subsalicylate)
name 2 eg of intestinal adsorbents
- kaolin
- diosmectite
moa of intestinal adsorbents
- adsorbents of bacteria, bacterial toxins and fluid
- decrease stool liquidity and amt
adverse effects of intestinal adsorbents
- constipation
- bind and inhibit absorption of other meds → do not take within 2h of other meds
name 1 formulation of lactobacillus acidophilus
lacteol fort
moa of lactobacillus acidophilus
adheres onto surface of intestinal cells and normalises intestinal flora by competitive exclusion
contraindication for lactobacillus acidophilus
lactose intolerance
name 1 bile salt-binding resin
cholestyramine
moa of bile salt-binding resins
bind to bile salts, alleviating diarrhoea caused by excess faceal bile salts
adverse effects of bile salt-binding resins
- bloating, flatulence, constipation
- exacerbation of malabsorption of fat
- binds to other drugs → do not give within 2h of other oral drugs
name 1 somatostatin-like peptide
octreotide
moa of somatostatin-like peptides
- inhibit release of various transmitters and hormones (eg. gastrin, VIP, 5-HT)
- reduce intestinal and pancreatic secretions
- slow GI motility and inhibit GB contraction
clinical use of somatostatin-like peptides
secretory diarrhoea caused by GI and neuroendocrine tumours
adverse effects of somatostatin-like peptides
- reduced pancreatic secretion → steatorrhoea → vit ADEK def
- nausea, abdo pain, flatulence, diarrhoea
- gallstones
- prolonged treatment → hypothyroidism
- bradycardia
use of charcoal
emergency treatment in poisoning (prevents absorption of poisons)
why charcoal might not stop diarrhoea
some contain sorbitol - worsens diarrhoea by increasing poison elimination
adverse effects of charcoal
- n&v
- aspiration → bronchiolitis obliterans, empyema, ARDS
- do not use LT (inteferes w absorption of nutrients/drugs)
drug used for paediatric diarrhoea
racecadotril
moa of racecadotril
- converted to thiophan (indir opioid agonist)
- reduces intestinal hypersecretion wo affecting motility
- decreases stool o/p wo causing constipation
adverse effects of racecadotril
nausea, vomiting, headache, rash
contraindications for racecadotril
- < 3mths
- persistent diarrhoea (>14 days)
- pts who had angioedema with ACE-I
- fructose intolerance
- glucose-galactose malabsorption syndrome
- sucrase-isomaltase insuffiency
