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F. Gastrointestinal Drugs > 2. Drugs used in Constipation & Diarrhoea > Flashcards

2. Drugs used in Constipation & Diarrhoea Flashcards

1
Q

What are the 7 major group of drugs used to treat constipation

A
  1. Bulk-forming laxative
  2. Stool surfactant agents
  3. Osmotic laxatives
  4. Stimulant laxatives
  5. Chloride channel activators
  6. Opioid receptor antagonist
  7. Serotonin 5-HT4 receptor agonists
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2
Q

Examples of bulk-forming laxatives

A
  1. Plant Products/Fibers:
    • Psyllium, Sterculia, Agar, Bran
  2. Semi-synthetic:
    • Methylcellulose
  3. Synthetic Fibers:
    • Polycarbophil
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3
Q

MOA of bulk forming agents

A
  1. Indigestible, hydrophilic colloids (fiber)
  2. Absorb water and form bulk, emollient gel that distends colon (increases stool mass)
  3. Promotes peristalsis
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4
Q

Main concerns / adverse effects of bulk forming agents

A
  1. Bacterial digestion of plant fibers within the colon may lead to flatus, bloating and abdominal pain
    • Avoid if suspected obstruction
  2. Interaction with absorption of other drugs
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5
Q

Examples of stool surfactant agents (softeners)

A
  1. Docusate (oral or enema)
  2. Glycerine (rectal suppository)
  3. Mineral oil (oral)
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6
Q

MOA of stool surfactant agents

A
  1. Lowers surface tension allowing water and lipids to penetrate
  2. Mineral oil lubricates + retards water absorption from stool
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7
Q

Main concerns / adverse effects of stool surfactant agents (softeners)

A

Mineral oil:

  1. Not palatable but may be mixed with fruit juice
  2. Aspiration can result in severe lipid pneumonitis
  3. Long-term use can impair the absorption of fat soluble vitamins (A,D,E and K)
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8
Q

Examples of osmotic laxatives

A
  1. Nonabsorbable sugars or salts
    - Sugars: Sorbitol, lactulose
    - Salts: Magnesium hydroxide; Magnesium citrate; Sodium phosphate
  2. Balanced Polyethylene Glycol (PEG): Balanced, isotonic solution of osmotically active sugar (PEG) and various salts
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9
Q

MOA of osmotic laxatives

A
  1. Osmotically-mediated water movement into bowel increases stool liquidity and volume
  2. Increased volume stimulates peristalsis
  3. High doses can produce bowel evacuation (purgation) within 1 to 3 hours
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10
Q

Main concerns/adverse effects of osmotic laxatives

A
  1. Colonic bacteria act on sugars → severe flatus and abdominal cramps
  2. Important to maintain adequate hydration by increasing oral fluid intake
  3. Sodium phosphate can cause:
    - Hyperphosphataemia, hypernatraemia and hypocalcaemia, hypokalaemia
    - Normally not clinically significant but may cause cardiac arrhythmias or acute renal failure due to tubular deposition of calcium phosphate (nephrocalcinosis)
    - 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

Balanced PEG is a safer alternative!

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11
Q

Examples of stimulant laxatives (cathartics)

A
  1. Anthraquinone derivatives
    - Aloe, Senna, Cascara (oral or per rectum)
    - Produce bowel movements in 6 to 12 hrs (oral) or 2 hrs (rectal)
  2. Diphenylmethane derivatives
    - Bisacodyl (oral or per rectum)
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12
Q

MOA of stimulant laxatives (cathartics)

A
  1. Produce migrating colonic contractions
  2. Mechanisms poorly understood but may include:
    • Direct stimulation of enteric nervous system
    • Colonic electrolyte and fluid secretion
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13
Q

Main concerns / adverse effects of stimulant laxatives

A
  1. Long-term use may be required in patients who are neurologically impaired or bed-bound
  2. Has been concern that chronic use may lead to dependence and destruction of myenteric plexus resulting in colonic atony and dilation but more recent evidence does not support this
  3. Anthraquinone Derivatives
    - chronic use leads to brown pigmentation of colon (melanosis coli)
    - has been concern regarding possible carcinogenesis but epidemiological studies do not support an association with colorectal cancer
  4. Diphenylmethane derivatives
    - phenolphthalein withdrawn due to cardiac toxicity
    - bisacodyl appears to be safe
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14
Q

Examples of chloride channel activators

A

Lubiprostone

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15
Q

MOA of chloride channel activators

A
  1. Stimulate type 2 chloride channels in small intestine
  2. Increase chloride-rich fluid secretions
  3. Stimulates motility and shortens intestinal transit time
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16
Q

Major concerns / adverse effects of chloride channel activators

A
  1. Return of constipation after discontinuation
  2. Avoid in pregnancy
  3. Nausea due to delayed gastric emptying
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17
Q

Examples of opioid receptor antagonist

A
  1. Methylnaltrexone bromide → administered subcutaneously every 2 days
  2. Alvimopan
18
Q

MOA of opioid receptor antagonists

A
  1. Effects mainly mediated through blockade of intestinal mu opioid receptors
  2. Do not readily cross the BBB so do not block CNS analgesic effects
19
Q

Major concerns / adverse effects of Alvimopan

A

Alvimopan → restricted to short-term use in hospitalised patients due to possible cardiovascular toxicity

20
Q

Example of 5-HT4-Receptor agonist

A
  1. Prucalopride

2. Cisapride

21
Q

MOA of 5-HT4-Receptor agonists

A

Stimulation of presynaptic 5-HT4 receptors on submucosal intrinsic primary afferent neurons (IPAN) terminals enhances release of neurotransmitters

  • E.g. calcitonin gene-related peptide (CGRP)
  • Stimulates enteric neurons (ENs) to promote peristaltic reflex and colonic mass movement
22
Q

Major concerns/adverse effects of 5-HT4-Receptor agonists

A

Cisapride:

  • 5-HT4 partial agonist
  • Adverse cardiovascular events due to actions at hERG K+ channel

Prucalopride:

  • High-affinity 5-HT4 agonist
  • Does not appear to have significant cardiovascular effects
23
Q

What are the 6 major antidiarrhoeal agents

A
  1. Opioid agonists
  2. Colloidal Bismuth Compounds
  3. Kaolin and Pectin
  4. Bile salt-binding resins
  5. Somatostatin-like peptides
  6. Lyophilizate of killed Lactobacillus acidophilus
24
Q

Examples of opioid agonists

A
  1. Loperamide

2. Diphenoxylate

25
Q

MOA of opioid agonists

A

Actions in the enteric nervous system increase colonic transit time

26
Q

Major concerns / adverse effects of opioid agonists

A

Potential for CNS effects including addiction and abuse

  • Loperamide → does not cross BBB
  • Diphenoxylate → At higher doses can have CNS effects and long-term use can lead to dependence → preparation with atropine to discourage overdose → leads to anticholinergic effects (e.g dry mouth) which can also contribute to antidiarrhoeal action
27
Q

Examples of colloidal bismuth compound

A
  1. Bismuth subsalicylate

2. Bismuth subcitrate potassium

28
Q

MOA of colloidal bismuth compounds

A
  1. Precise mechanisms of action not known
  2. Bismuth has antimicrobial effect and binds enterotoxins which has benefit for treating traveller’s diarrhoea
  3. Bismuth compounds also used as mucosal protective agents in acid-peptic diseases (e.g. peptic ulcers)
  4. Bismuth subsalicylate:
    • Rapid dissociation in stomach allowing absorption of salicylate
    • Salicylate inhibits intestinal prostaglandin production and chloride secretion
    • Reduces stool frequency and liquidity in acute infectious diarrhoea
29
Q

Major concerns / adverse effects of colloidal bismuth compounds

A
  1. Although > 99% of bismuth is eliminated in stool <1% is absorbed and stored in many tissues, elimination is by slow renal excretion
  2. But generally safety profile of bismuth formulations is good
  3. Harmless blackening of the stool, which may be confused for
    gastrointestinal bleeding
  4. Harmless darkening of tongue (liquid formulations)
  5. Prolonged use may rarely produce bismuth toxicity resulting in encephalopathy (ataxia, headaches, confusion, seizures)
    • Use only for short periods
    • Avoid in patients with renal insufficiency
  6. Salicylate toxicity with high does of bismuth subsalicylate
30
Q

MOA of kaolin and pectin

A
  1. Absorbents of bacterial toxins and fluid
  2. Decrease stool liquidity and number
  3. Useful in acute diarrhoea but seldom used chronically
31
Q

Major concerns / adverse effects of kaolin and pectin

A
  1. Not absorbed so little risk of significant adverse effects
  2. Constipation is only likely adverse effect
  3. Can bind to and inhibit absorption of other medications:
    - should not be taken within 2hours of other medications
32
Q

Examples of bile salt-binding resins

A
  1. Cholestryamine
  2. Colestipol
  3. Colesevelam
33
Q

MOA of bile salt-binding resins

A
  1. Conjugated bile salts are normally absorbed in the terminal ileum
  2. Disease of the ileum (e.g. Crohn’s disease) or surgical resection leads to malabsorption of bile salts resulting in colonic secretory diarrhoea
  3. Bile salt-binding resins bind to bile salts alleviating diarrhoea caused by excess fecal bile salts
34
Q

Major concerns / adverse effects of bile-salt binding resins

A
  1. Bloating, flatulence, constipation and fecal impaction
  2. Exacerbation of malabsorption of fat if underlying deficiency is present
  3. Cholestyramine and Colestipol bind to a number of drugs and should not be given within 2hrs of other drugs
35
Q

Examples of somatostatin-like peptides

A

Octreotide

36
Q

MOA of somatostatin-like peptide

A
  1. Somatostatin is a 14-amino acid peptide released in the GI tract and pancreas and from the hypothalamus
  2. Wide-spread physiological effects including:
    - 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
  3. Use for secretory diarrhoea caused by gastrointestinal neuroendocrine tumours (carcinoid and VIP-oma)
  4. Can also treat diarrhoea due to vagotomy, gastric dumping syndrome, short bowel syndrome and AIDs
37
Q

Major concerns / adverse effects of somatostatin-like peptides

A
  1. Impaired pancreatic secretion can cause steatorrhoea → lead to fat-soluble vitamin deficiency
  2. Nausea, abdominal pain, flatulence and diarrhoea
  3. Formation of gall sludge or gallstones in 50% of patients, rarely leading to acute cholecystitis
  4. Prolonged treatment can result in hypothyroidism
  5. Bradycardia
38
Q

Example of lysophilizate of killed lactobacillus acidophilus

A

Lacteol forte

39
Q

MOA of lacteol forte

A
  1. Use in bacterial or “traveler’s diarrhoea”
  2. Preparation contains heat-inactivated Lactobacillus acidophilus
  3. Adheres onto the surface of intestinal cells and normalizes the intestinal flora by competitive exclusion
  4. By interfering with the intestinal adherence of other micro-organisms, over colonization of these organisms is prevented
40
Q

Major concerns / adverse effects of lacteol forte

A
  1. Not systemically absorbed therefore little risk of adverse effects
  2. Important to maintain hydration
  3. Contraindicated in patients with lactose intolerance as formulation contains lactose monohydrate
41
Q

Does activated charcoal prevent diarrhoea

A

Has not shown to be effective in relieving diarrhoea in controlled clinical trials and meta-analyses

F. Gastrointestinal Drugs (3 decks)

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