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Lower GI drugs Flashcards

1
Q

Important regulators of motility and water absorption

A
  • -Acetylcholine
  • -Serotonin
  • -Dopamine
  • -Enkephalins
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2
Q

Where is 5HT released from?

A

Enterochromaffin Cells (function as sensory receptors)

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3
Q

What drugs work at the level of the sensory neurons?

A

SSRI’s, bulk-forming laxatives, contact cathartics, 5HT3 antagonists, 5HT4 agonists

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4
Q

Afferent neuron NTs

A

cGRP, glutamate, substance P

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5
Q

5HT

A

Major player in lower GI pathology, especially IBS

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6
Q

SSRI drug names

A

Fluoxetine, paroxetine, sertraline

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7
Q

What are SSRI’s most beneficial in treating (related to GI)?

A

–Constipation predominant IBS

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8
Q

Mechanism of SSRIs in GI system

A

Decrease reuptake of 5HT into EC cells –> increase 5HT in synapse–> increase afferent activity –> increase peristalsis

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9
Q

Bulk laxative names

A

Dietary fiber, methylcellulose, polycarbophil, psyllium

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10
Q

Bulk laxative MOA

A
  • -Drugs that attract H2O and increase stool mass
  • -Act as “stool stabilizers”
  • -Increase lumen distention
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11
Q

How do bulk laxatives act on diarrhea?

A

Decrease bowel movements, make stool more solid and decrease pain

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12
Q

How do bulk laxatives act on constipation?

A

Increase bowel movements, makes stool more loose, decrease pain

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13
Q

What factors limit the use of bulk laxatives?

A
  1. Neurons generating peristaltic reflex must be functional (enteric system must be working)
  2. Cause of constipation must be known
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14
Q

Side effects of bulk laxatives

A

Allergies, increased flatulence, increased obstruction

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15
Q

Contact cathartic names

A

Anthraquinone derivatives, bisacodyl, castor oil

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16
Q

Anthraquinone derivative names

A

Casacara sagrada, danthron, senna

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17
Q

Bisacodyl

A
  • -Prodrug
  • -Almost 6 hr latency to effect
  • -Acts on large intestine
  • -Less potent than castor oil
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18
Q

Anthraquinones

A
  • -Act on large intestine

- -Less potent than castor oil

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19
Q

Castor oil

A
  • -Acts on both small and large intestine
  • -Short latency
  • -Extremely potent effects
  • -More significant side effects
  • -Activate ricinoteric acid
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20
Q

Contact cathartic MOA?

A

Thought to be irritation of mucosa

Not sure if dependent on enteric nervous system

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21
Q

Side effects of contact cathartics

A
  • -Dependency (can’t have BM until take the drug)
  • -Destroy myenteric plexus long term
  • -Pigmentation of the mucosa (“melonosis coli”)
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22
Q

Additional side effects of castor oil

A

Dehydration, electrolyte imbalance, uterine contractions

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23
Q

5HT3 receptor antagonist

A

Alosetron

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24
Q

Alosetron MOA

A
  • -Decrease afferent stimulation–> decreases peristalsis

- -Longer duration of action than antiemetic

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25
Q

Alosetron therapeutic uses

A

Diarrhea predominant IBS

  • -Only used when everything else has failed
  • -Restricted use (compassionate use only)
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26
Q

Alosetron side effects

A
  • -Constipation (30% of patients, 10% must stop drug, 0.1% require hospitalization)
  • -0.3% develop ischemic colitis–> can be fatal, increased with inhibitors and substrates of Cyp1A2
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27
Q

5HT4 receptor agonists

A

Cisapride (also a 5HT3 antagonist) and tegaserod (more selective)

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28
Q

5HT4 receptor agonists MOA

A

Receptors located on presynaptic terminals–> increase release of NT from afferent neurons–> increase peristalisis

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29
Q

5HT4 receptor agonists therapeutic use

A
  • -Used when no other options available, restricted availability
  • -Tegaserod: constipation predominant IBS
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30
Q

5HT4 receptor agonist side effects

A
  • -CV toxicity (esp. arrhythmias–long QT)

- -85% w/long QT had pre-existing conditions and/or admin of Cyp3A4 inhibitors

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31
Q

Opiates (that work in GI system) drug names

A
  • -Loperamide

- -Diphenoxylate

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32
Q

Opiate action in GI system

A

Decrease both GI motility and water excretion and are the most effective antidiarrheal drugs

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33
Q

Can loperamide or diphenoxylate cross the BBB?

A

Loperamide cannot, but diphenoxylate can sort of cross the BBB (so given via prescription)

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34
Q

What can be used to offset the constipation caused by opiate analgesics?

A

Alvimopan and methylnaltroxone

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35
Q

What are the Mu receptor antagonists?

A

Alvimopan and methylnaltroxone

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36
Q

Opiate MOA

A
  • -Inhibition of motility and secretion

- –Generally don’t cross the BBB very well

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37
Q

Why is diphenoxylate usually given with atropine?

A

Atropine blocks muscarinic receptors–> decreases contraction and also has unpleasant side effects making it less likely to be abused

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38
Q

Therapeutic uses of opiates in GI system?

A

–Most effective antidiarrheals and good against most forms of diarrhea

39
Q

Side effects of opiates

A
  • -Abdominal cramps
  • -TOXIC MEGACOLON if pt has ulcerative colitis
  • -HIGH doses of diphenoxylate–> euphoria –> can lead to physical dependence
40
Q

Mu receptor antagonists MOA

A
  • -Don’t cross BBB

- -Selective antagonists

41
Q

Therapeutic uses of Mu receptor antagnoists

A
  • -Constipation caused by opiate therapy
  • -Alvimopan: short-term use in hospitalized patients
  • -Methylnaloxone: long-term palliative care
42
Q

Alvimopan side effects

A

Increased risk of MI

43
Q

D2 receptor antagonist drug names

A

Domperidone (doesn’t cross BBB)

Metoclopramide (most widely available in the US)

44
Q

D2 receptor antagonist MOA

A

–Cholinomimetics (increased actions of Ach in gut –> inhibition of DA inhibition–> increases motility in entire gut–> prokinetic

45
Q

Domperidone therapeutic uses

A

–Compassionate use only in US. Impaired motility, esp. decreased gastric emptying (e.g . from vagotomy, diabetic gastroparesis)

46
Q

Metoclopramide use

A

Antiemetic

47
Q

D2 receptor antagonist side effects

A

–Somnolence, nervousness, agitation, anxiety, dystonia, tardive dyskinesia (irreversible), parkinsonism, increased prolactin release (menstrual disorders, impotence, galactorrhea)

48
Q

TCA’s MOA

A
  • -Decrease reuptake of postganglionic sympathetic neurons –> increase activation of alpha2 on presynaptic terminals of Ach postganglionic parasympathetic nerves–> decrease Ach release–> decrease motility.
  • -Decrease reuptake of DA–> increases activation of D2 receptors
49
Q

TCA drug names

A

Amitriptyline and desipramine

50
Q

What drugs stimulate motilin?

A

Macrolide antibiotics (eg erythromycin)

51
Q

What drugs influence chloride secretion?

A

Lubiprostone, linaclotide, crofelemer, octreotide, bismuth subsalicylate, opiates.

52
Q

How do osmotic cathartics and bile acid binding resins work?

A

Increasing or reducing the osmotic load in the colon

53
Q

MOA of lubiprostone

A
  • -Activates ClC-2–> increases Cl- secretion

- -Poorly absorbed–> almost no systemic effects

54
Q

Lubiprostone therapeutic uses

A

Chronic constipation and constipation-predominant IBS

55
Q

Lubiprostone side effects

A
  • -Diarrhea
  • -Nausea/HA
  • -Increased fetal loss–NOT for use during pregnancy
56
Q

Linaclotide MOA

A
  • -Activates guanylyl cyclase C (cGMP)–> activates CFTR–> increases Cl- secretion–> increases H2O lumen
  • -Very little systemic absorption
57
Q

Linaclotide therapeutic uses

A

Chronic constipation and constipation-predominant IBS

58
Q

Linaclotide side effects

A

Diarrhea
Increased maternal death
Increased mortality of juvenile mice (contraindicated in peds)

59
Q

Crofelemer MOA

A
  • -Voltage dependent inhibition of CFTR (and another Cl- channel)–> decreases Cl- secretion–> decreases Na+/H2O excretion–> firmer stool
  • -Little systemic absorption
60
Q

Crofelemer therapeutic uses

A

Diarrhea from anti-HIV drug treatment

61
Q

Somatostatin analogue drug name

A

Octreotide

62
Q

Octreotide MOA

A

Synthetic: longer T1/2 than somatostatin. Decreases fluid secretion. Low doses increase motility, high doses decrease motility

63
Q

Octreotide therapeutic uses

A

Off label: SEVERE diarrhea from dumping syndrome, short bowel syndrome, vagotomy, AIDS

64
Q

Octreotide side effects

A
  • -Impaired pancreatic secretion–> decreased fat absorption (can cause fat soluble vitamin deficiency)
  • -decreased GI motility (dose dependent)–> nausea, abdominal pain, flatulence
  • -decreased gallbladder contractility–> gallstones (50%), acute cholecystitis (rare)
  • -Insulin/glucagon imbalance
  • -Hypothyroidism and bradycardia
65
Q

Bismuth subsalicylate MOA

A

Salicylate decreases PG and Cl- secretion in LARGE INTESTINE, antimicrobial, bind enterotoxins

66
Q

Bismuth subsalicylate therapeutic uses

A

PREVENTION and tx of traveller’s diarrhea

67
Q

Bismuth subsalicylate side effects

A
  • -Blackening of stool and tongue

- -High doses: salicylate toxicity: tinnitus, acid-base disturbances etc.

68
Q

Osmotic cathartic drug names

A

Lactulose, magnesium hydroxide, sodium phosphate, polyethylene glycol electrolyte solution

69
Q

Osmotic cathartic MOA

A

Not absorbed–> increased H2O in lumen by osmosis

70
Q

Osmotic cathartic therapeutic uses

A

–Constipation: especially when enteric nervous system disrupted

71
Q

Lactulose therapeutic uses

A

Decreases [ammonia]–> treats portal systemic encephalopathy

72
Q

What can occur if osmotic laxatives are absorbed systemically?

A

Intravascular volume depletion and electrolyte imbalances (hyperphosphatemia, hypocalcemia, hypernatremia, hypokalemia).

73
Q

Who should osmotic cathartics be used with caution in?

A

Elderly, frail, have renal insufficiency or have significant cardiac disease

74
Q

What can Mg(OH)2 cause in patients with kidney failure?

A

Hypermagnesemia

75
Q

Lactulose side effects

A

Metabolized by gut bacteria–> SEVERE cramps, flatulence, discomfort

76
Q

Bile acid binding resin drug names

A

Cholestyramine, colestipol

77
Q

Bile acid binding resin MOA

A
  • -Decreased reabsorption of bile salts–> secretory diarrhea (Crohn’s disease or resection of terminal ileum)
  • -Bind unabsorbed bile acids–> decreases H2O secretion
78
Q

Bile acid binding resin side effects

A
  • -Bloating, flatulence, constipation, fecal impaction

- -Impairing absorption of other drugs and fat soluble vitamins

79
Q

Stool softener names

A

Docusate, mineral oil

80
Q

Docusate MOA

A

Surfactant

81
Q

Mineral oil MOA

A

Lubricates

82
Q

Stool softener therapeutic uses

A

Widespread clinically. Questionable effectiveness in all scenarios

83
Q

When should stool softeners not be used?

A

Cases of undiagnosed abdominal pain or unknown intestinal pathology

84
Q

Side effects of Mineral Oil

A 
Lipid pneumonitis (if aspirated) 
Can cause decreased absorption of fat soluble vitamins
85
Q

Prokinetics

A

Decrease motility throughout entire GI tract (not just the colon)

86
Q

Types of prokinetics

A
  1. D2 receptor antagonists (metoclopramide)
  2. Macrolides (erythromycin)
  3. 5HT4 agonists (Cisapride–restricted use)
87
Q

Prokinetic uses

A

Impaired gastric emptying and constipation (decreased motility in entire GI tract)

88
Q

Where are antidiarrheals NOT recommended?

A

Bloody diarrhea, high fever, systemic toxicity

89
Q

What should prescription of laxatives be secondary to?

A

Dietary modifications, increasing fluid uptake, and physical activity

90
Q

What has a mild effect and long latency?

A

Laxatives

–Softening of feces (1-3 days)

91
Q

What has an intermediate effect and latency?

A

Contact cathartics

–Semi-solid, soft stool (6-8 hrs)

92
Q

What has a strong effect and short latency?

A

Osmotic cathartics and castor oil

–Watery evacuation (1-3 hrs)

93
Q

Constipation predominant IBS treatment

A

Laxatives and cathartics. Tegaserod can be used (restricted availability)

94
Q

Diarrhea predominant IBS treatment

A

Opiates. Alosetran can be used (restricted availability)

GI (12 decks)

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