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Yr 2 Gastrointestinal > Wk 3 - Pharmacology: Diarrhoea and Constipation > Flashcards

Wk 3 - Pharmacology: Diarrhoea and Constipation Flashcards

1
Q

What are the three main causes of diarrhoea?

A
  1. Infection: bacteria, virus, parasite
  2. Medications - 7% of adverse reactions
  3. Chronic bowel disorders
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2
Q

List some of the main infective diarrhoeal diseases?

A
  1. Bacteria: E.coli, Salmonella enteriditis/typhi, Vibrio cholera, Campylobacter jejuni, C.difficile, Shigella
  2. Virus: Norwalk virus, Rotavirus, Adenovirus
  3. Parasites: Cryptosporidium parvum, Entamoeba histolytica
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3
Q

What is the most common infective diarrhoeal disease in under 2s?

A

Rotavirus and Bacteria

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4
Q

What is the most common infective diarrhoeal disease in adults?

A
  • Viral
  • Bacteria
  • Camyplobacter
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5
Q

Describe what happens in infective diarrhoeal disease.

A
  • There is malabsorption of water and nutrients, which leads to dehydration and malnutrition.
  • Changes to gut wall - affect absorption.
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6
Q

List some medications that cause diarrhoea.

A
  1. Cholinergics - increase ACh
  2. Cytotoxic agents - loss of gut epithelia
  3. Broad-spectrum antibiotics - change in gut flora
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7
Q

What are some chronic bowel disorders that affect diarrhoea and also constipation?

A
  • IBD - ulcerative colitis and Crohns
  • Endocrine disease - diabetes and thyroid disease
  • IBS
  • Diverticular disease
  • Malabsorption syndromes eg coeliac disease, pancreatic insufficiency, cystic fibrosis
  • Psychological eg stress
  • Self-induced laxative abuse
  • Antibiotic-associated colitis
  • Chemotherapy GI irradiation
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8
Q

What are the physiological outcomes of diarrhoea?

A
  1. Dehydration – H2O, Na loss + cannot reuptake Na
  2. Metabolic acidosis – HCO3 loss
  3. Potassium depletion – K (hypokalaemia)
  4. Hypovolaemia
  5. Cardiovascular collapse
  6. Death
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9
Q

List the signs of dehydration (95% vs 90% dehydration).

A

95% dehydration:

  • Thirst
  • Skin turgor (worse as we age tho)
  • Tachycardia
  • Dry mucous membranes
  • Sunken eyes
  • LAck of tears
  • Sunken anterior fontanelle (hole at the top of the head)
  • Oliguria (good indicator esp in infants and children)

90% dehydration – life-threatening:

  • Anuria
  • Hypotension
  • Feeble and very rapid radial pulse
  • Cool and moist extermities
  • Diminished conciousness
  • Signs of hypovolaemic shock – leading to death
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10
Q

How is acute diarrhoea treated?

A
  1. Oral rehydration therapy – prevention or reversal of dehydration
  2. Antimotility drugs – relieve symptoms (not recommended in children + sometimes issue when the cause is infective as want to get rid of infective agent)
  3. Antisposmadics – reduce cramping and pain
  4. Antibacterials – usually no requires in simple episodes
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11
Q

What is oral rehydration therapy composed of?

A
  • Na
  • Glucose
  • K
  • Citrate
  • Cl
    • clean water

Usually isotonic then maybe hypotonic when rehydrated

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12
Q

What is the priority in acute diarrhoea?

A

Prevention or reversal of dehydration particularly in elderly and children

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13
Q

Why/how does oral rehydration therapy work?

A
  • ORS works because of the Sodium-Glucose Co-Transport System (SGLT1)
  • The co-transport of Na into epithelial cells via SGLT1 requires glucose
  • Two Na ions and one glucose are transported together across the membrane via the SGLT1 protein
  • Then Na/K ATPase transports Na back into blood and K into epithelial cells
  • Wherever Na goes, H2O follows
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14
Q

What are antimotility drugs?

A

Antimotility agents are drugs used to alleviate the symptoms of diarrhoea. They increase muscle tone but diminish propulsive activity + reduced awareness of urge.

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15
Q

What is the mechanism of action of antimotility drugs?

A

They bind to the μ opioid receptor in the submucosal plexus of the intestinal wall

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16
Q

List some antimotility drugs.

A

All opiates

  • Codeine
  • Morphine
  • Loperamide - relatively selective in GI tract, reduced BBB and central activity (so no euphoria)
  • Cophenotrope
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17
Q

What are some S/Es of antimotility drugs?

A

Nausea, vomiting, cramps, paralytic ileus (problem esp in Crohns)

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18
Q

What are antispasmodics?

A

Muscarinic antagonists that inhibit gastric emptying

19
Q

List some examples of antispasmodics.

A
  • Atropine (not really used for diarrhoea relief)
  • Propantheline
  • Dicycloverine
20
Q

In which condition are antispasmodics mostly used?

A

In IBS to reduce GI motility and spasms

21
Q

How do antispasmodics work ie mechanism of action?

A

Blocking parasympathetic action of the myenteric and submucosal neural plexus

22
Q

When would you normally prescribe antibiotics for a diarrhoeal episode?

A

Travellers diarrhoea give co-trimoxazole as prophylaxis

23
Q

What do you prescribe for pseudomembranous colitis or c.difficile?

A

Metronidazole or vancomycin

24
Q

What organism causes the majority of diarrhoeal disease?

A

Viruses

25
Q

What is the most important aspect of the treatment of diarrhoea?

A

Prevent dehydration using ORT

26
Q

What is the mechanism of action of antimotility drugs?

A

Diminish propulsive activity via mu opioid receptor

27
Q

List some reasons causing constipation.

A
  • Disease
  • Dehydration
  • Ignoring the urge
  • Laxative abuse
  • Travel
  • IBS
  • Milk
  • Medications
  • Reduced physical activity (elderly)
  • Chronic idiopathic constipation
  • Colon or rectal problems
28
Q

Constipation is most common among…

A
  1. Women (due to hormone changes)
  2. Over 65s (due to reduced physical activity)
  3. During and after pregnancy
29
Q

List some diseases associated with constipation.

A
  1. Neurological: MS, PD, Stroke, Spinal cord injury, Chronic idiopathic injury
  2. Metabolic/endocrine: Diabetes, Poor glycaemic control, Uraemia, Hyperkalaemia, Hypothyroidism
  3. Systemic disease: Amyloidosis, Lupus, Scleroderma

All generally lead to slower movement of stool through the colon

30
Q

List some medications that cause consipation.

A
  1. Pain meds (narcotics)
  2. Diuretics
  3. Antisposmadics
  4. Aluminium antacids
  5. Antidepressants
  6. Iron supplements
  7. Antiepileptics
31
Q

List the types of agents used to treat constipation (4).

A
  1. Bulk formers
  2. Stimulants
  3. Osmotics
  4. Foecal softners
32
Q

What are bulk-forming laxatives?

A
  • Unprocessed wheat bran OR
  • Ispaghula husk
  • Methylcellulose (also softener)
  • Sterculia polysacchride polymers
33
Q

How do bulk-forming laxatives relieve constipation?

A
  • Increasing foecal mass: bacterial proliferation and hydrophilic action
  • Stimulates peristalsis (reaction to mechanical stretch)
34
Q

List some stimulants used to relieve constipation.

A
  • Bisacodyl
  • Dantron
  • Senna

Decreasing order of stimulation

35
Q

How do stimulants work?

A

They increase intestinal motility. Anthraquinone group (dantron and senna) also stimulate smooth muscle activity.

Stimulate myenteric nerve plexus, increase gut motility, water and electrolyte transfer

36
Q

How long does it take for stimulants to take effect?

A

Usually 6-12hrs (Bisacodyl - 15 to 30 mins rectal admin)

37
Q

List some foecal softeners.

A
  • Liquid paraffin (not used anymore)
  • More used Arachis oil
38
Q

Traditionally liquid paraffin was used as a foecal softener but not anymore because of…

A
  1. Anal seepage and anal irritation
  2. Granulomatous reaction
  3. Lipoid pneumonia
  4. Reduced lipid-soluble vitamin uptake
39
Q

How do osmotic laxatives work?

A
  • Withdraw fluid from the bowel or retain the fluid they are administered with
  • Accelerate transfer through small intestine, large volume in colon
40
Q

List most commonly used osmotic laxatives.

A

Usually sugar or saline preparations

  • Lactulose - metabolised by gut bacteria - lactic and acetic acid have osmotic action (24hr)
  • Macrogols - ethylene glycol sequesters fluid - causes dehydration (so need extra fluid)

Also magnesium salts - rapid, need adequate fluid intake, often abused + can cause central effects in overdose

41
Q

What are bowel cleansers and when are they used?

A
  • Sodium acid phosphate, Sodium picosulfate.
  • Used before colonic surgery, colonoscopy, radiology.
42
Q

What are three potential side effects of stimulant laxatives?

A

Cramps, diarrhoea on long-term use, tolerance

43
Q

Who can be constipated?

A

Anyone but more in older, sedentary, pregnant, post-surgery, women, medication

Yr 2 Gastrointestinal (37 decks)

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