GIT - constipation and diarrhoea Flashcards by Pang YongTing

Drugs for CONSTIPATION (7)

(BOSS COS)
Bulk-Forming Laxatives - increase water in stools
Osmotic Laxatives - increase water in stools
Stool Surfactant Agents (Softeners) - increase water in stools
Stimulant Laxatives - promote peristalsis/motility
Chloride Channel Activators - promote peristalsis/motility
Opioid Receptor Antagonists - promote peristalsis/motility
Serotonin 5-HT4-Receptor Agonists - promote peristalsis/motility

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Bulk forming agents

plant products/ synthetic fibres:
Psyllium
Methylcellulose
Polycarbophil

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bulk forming agents MOA

Indigestible, hydrophilic colloids (fiber)
Absorb water and form bulk, emollient gel that distends colon (increases stool mass)
Promotes peristalsis -> get rid of food more easily

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Stool Surfactant Agents (Softeners)

Docusate (oral or enema - fluid through rectum)
Glycerin (rectal suppository - solid medication through rectum)
Mineral oil (oral)

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Stool Surfactant Agents (Softeners) MOA

Lowers surface tension allowing water and lipids to penetrate
Mineral oil lubricates + retards water absorption from stool - so stools still fluid to be passed out

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Stool Surfactant Agents (Softeners) concerns

Aspiration can result in severe lipid pneumonitis

Long-term use can impair absorption of fat soluble vitamins (A, D, E and K)

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Osmotic Laxatives

nonabsorbable sugars/salts - sorbitol, lactulose, Mg(OH)2, sodium phosphate
polyethylene glycol (PEG)** - balanced with osmotically active sugars -> better choice! avoids significant electrolyte shifts

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osmotic laxatives MOA

Osmotically-mediated water movement into bowel increases stool liquidity and volume
Increased volume stimulates peristalsis
High doses can produce bowel evacuation (purgation) within 1 to 3 hours

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osmotic laxatives ADR

colonic bacteria act on the introduced sugars -> flatus and abdominal cramps
need to maintain adequate hydration
sodium phosphate: hypernatremia, hypocalcemia, hypokalaemia
may cause cardiac arrhythmias or acute renal failure due to tubular deposition of calcium phosphate

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osmotic laxatives (sodium phosphate) contraindications

Should not be used in patients who are frail, elderly, on diuretics, unable to maintain adequate hydration or who have renal insufficiency or cardiac disease

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Stimulant Laxatives (Cathartics)

Anthraquinone Derivatives:
Aloe, Senna and Cascara (oral or per rectum)
Diphenylmethane Derivatives:
Bisacodyl (faster bowel movement effect if done through rectum, also can be oral): used for bowel prep before colonoscopy

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Stimulant Laxatives MOA

Produce migrating colonic contractions

Colonic electrolyte and fluid secretion

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Stimulant Laxatives ADR

chronic use may lead to dependence -> long term use

brown pigmentation of the colon

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Chloride Channel Activators drug

Lubiprostone

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Chloride Channel Activators MOA

Stimulate type 2 chloride channels (ClC-2) in small intestine
Increases chloride-rich fluid secretions
Stimulates motility and shortens intestinal transit time

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Chloride Channel Activators ADR + contraindication

return of constipation after discontinuation of drug
nausea caused by delayed gastric emptying
NO PREGNANCY

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Opioid Receptor Antagonists

Methylnaltrexone bromide - more for palliative patients
1st line for cancer!!* subcutaneous injection every 2 days

Alvimopan - post GI surgery:
Orally ≤5 hrs before surgery & twice daily after surgery (not >7 days)

Opioid Receptor Antagonists MOA

treatment for opioid induced constipation
blockade of intestinal mu (μ) opioid receptors
– Does not readily cross blood-brain barrier so do not block CNS analgesic effects**

Opioid Receptor Antagonists ADR

only for short term use in hospitalised patients cause of risk of CVS toxicity

5-HT4-Receptor Agonists drugs (2)

Cisapride

Prucalopride

5-HT4-Receptor Agonists MOA

Stimulation of presynaptic 5-HT4 receptors on submucosal intrinsic primary afferent neurone (IPAN) terminals enhances release of neurotransmitters -> stimulate enteric neurons (EN) to promote peristaltic reflex and colonic mass movement

5-HT4-Receptor Agonists ADR

Cisapride: partial agonist. adverse CVS effects due to actions at hERG K+ channel
Prucalopride: high affinity agonist. no CVS effects

Drugs for diarrhoea

(BLOCKS)
Opioid Agonists - time
Colloidal Bismuth Compounds - stool freq and liquidity
Kaolin (clay) and Pectin (indigestable carbohydrate from apples) - stool liquidity
Bile Salt-Binding Resins
Somatostatin-like Peptides - motility
Lyophilizate of killed Lactobacillus acidophilus - intestinal flora

Opioid Agonists drugs (2)

Loperamide

Diphenoxylate

Opioid Agonists MOA

effects in ENS (enteric nervous system): increase colonic transit time

Opioid Agonists ADR

CNS effects: addiction and abuse; dependence - for diphenoxylate: given with atrophine (se: dry mouth) to discourage overdose

Colloidal Bismuth Compounds

Bismuth subsalicylate | Bismuth subcitrate potassium

Colloidal Bismuth Compounds MOA

has antimicrobial effect and binds enterotoxins which has benefit for treating traveller’s diarrhoea mucosal protective agents in acid-peptic diseases salicylate: inhibits intestinal prostaglandin production and chloride secretion, reduces stool frequency and liquidity in acute infectious diarrhoea - more solid poop

Kaolin and pectin MOA

Absorbents of bacterial toxins and fluid Decrease stool liquidity and number for acute diarrhoea

Kaolin and pectin ADR

bind to and inhibit absorption of other medications -> should not be taken within 2hrs of other medication not absorbed so less risk of adverse effects

Bile Salt-Binding Resins (3)

Cholestryamine colestipol colesevelam

Bile Salt-Binding Resins MOA

bind to bile salts alleviating diarrhoea caused by excess fecal bile salts - because of malabsorption of bile salts due to disease of the ileum (conjugated bile salts are normally absorbed in the terminal ileum)

Bile Salt-Binding Resins ADR

Bloating, flatulence, constipation and fecal impaction Exacerbation of malabsorption of fat if underlying deficiency is present affects absorption of other medication -> take 2hrs apart

Somatostatin-like Peptide drugs (2)

somatostatin (super short - 3min - T1/2 through IV) | Octreotide (longe T1/2=1.5hrs)

Somatostatin-like Peptides MOA

Inhibition of release of various transmitters and hormones (e.g. gastrin, VIP, 5-HT) Reduces intestinal and pancreatic secretions Slows gastrointestinal motility and inhibits gallbladder contraction For secretory diarrhoea caused by gastrointestinal neuroendocrine tumours/ vagotomy/ gastric dumping syndrome (rapid gastric emptying)/ short bowel syndrome/ AIDS

Somatostatin-like Peptides ADR

reducing pancreatic secretions: cause steatorrhea -> fat-soluble (ADEK) vit def Nausea, abdominal pain, flatulence and diarrhoea Formation of gall sludge or gallstones in 50% of patients Prolonged treatment can result in hypothyroidism/ bradycardia

Lyophilizate of killed Lactobacillus acidophilus

Lacteol forte - mixed w/ water

Lyophilizate of killed Lactobacillus acidophilus MOA

for travellers diarrhoea Adheres onto the surface of intestinal cells and normalizes the intestinal flora by competitive exclusion Prevents over colonization of these organisms

Lyophilizate of killed Lactobacillus acidophilus ADR | + contraindication

not systemically absorbed = little risk of ADR need to maintain hydration contraindicated in pts with lactose intolerance

Activated charcoal MOA

used for emergency treatment of certain types of poisoning: prevents poison from being absorbed from the stomach into the body not proven to treat diarrhoea yet - might bind to enterotoxins and prevent infectious diarrhoea?

Activated charcoal ADR

nausea and vomitting risk of charcoal entering the lungs -> respiratory side effects: bronchiolitis obliterans, empyema, and Adult Respiratory Distress Syndrome interferes with absorption of other nutrients/drugs