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GI Pharm > GI Laxatives/Anti-diarrheals/Anti-emetics > Flashcards

GI Laxatives/Anti-diarrheals/Anti-emetics Flashcards

1
Q

Physiology of water secretion/absorption/secretion in GI tract?

A

a. 9L of water enter gut per day→2L from diet + 7L secreted from body
b. All but 1L absorbed in small intestine (J&I)
c. 1L enters colon, which absorbs ~900 mL
d. Only ~100-200 mL of water normally excreted in stool each day.

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2
Q

5 Type of Laxatives?

A

Laxatives (increase water in stool or stimulate muscle; constipation = too little water in stool)

  1. Dietary Fiber and Bulk-forming laxatives
  2. Surfactant laxatives
  3. Osmotic laxatives→a. Mg-containing b. PEG-electrolyte solutions
  4. Stimulant laxatives→the most potent class
  5. Miscellaneous laxatives
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3
Q

MoA of dietary fiber and bulk-forming laxatives? (3)`

A

Increase volume and stimulate evacuation
1. Increase delivery of water into the colon (retains water)
2. Increase bulk (distention→reflex contraction of bowel)
3. Decrease pressure in the sigmoid colon
Net Result = more formed stools

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4
Q

Bulk-forming laxative agents? (3)

A
  1. Psyllium husk
  2. Methyl-cellulose (semisynthetic cellulose)
  3. Polycarbophil
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5
Q

Psyllium: characteristics and ADEs?

A

a. Characteristics: hydrophilic muciloid that forms gelatinous mass when mixed with water
b. ADEs:
1. Allergic rxns
2. Flatulence
3. Borborygmi
4. Intestinal obstruction
5. May inhibit Coumarin absorption

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6
Q

Methyl-cellulose: characteristics and ADEs?

A

a. Characteristics: Hydrophilic and digestible; forms a colloid mass with water
b. ADEs:
1. May bind an impede drug absorption

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7
Q

Polycarbophil: characteristics and ADEs?

A

a. Characteristics: hydrophilic polyacrylic resins; absorb 60-100x their weight in water
b. ADEs:
1. Ca2+ polycarbophils release Ca which is contraindicated with Tetracycline

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8
Q

Surfactant laxative agents?

A 
Lubricate/soften stool, ease passage
1. Docusates (aka Diocytl Sodium Sulfosuccinate)
2. Poloxamers
3. Castor Oil
Glycerin suppositories?? Mineral Oil??
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9
Q

Characteristics and ADEs of Docusates (Dioctyl Sodium Sulfosuccinate)?

A

a. Characteristics:
1. Anionic surfactant; weakly active
2. Primary use = stool softener to reduce the strain of defecation
3. No effect on intestinal peristalsis
b. ADEs:
1. NOT for use during abdominal pain, or n/v
2. Can irritate intestinal mucosa and increase intestinal absorption of other drugs→recommended for short-term use

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10
Q

Poloxamers: characteristics and ADEs?

A

a. Characteristics: Non-ionic surfactant; similar to docusates; stool softener
b. ADEs:
1. Diarrhea
2. Not for use during abdominal pain or n/v

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11
Q

Characteristics and ADEs of Castor Oil?

A

a. Characteristics:
1. Rapid-acting and effective anionic surfactant that produces CATHARSIS (complete evacuation of bowels)
2. Stimulates intestinal peristalsis
b. ADEs:
1. Colic
2. Dehydration (drink alot of H2O)
3. Electrolyte imbalance w/ overdose
4. Contraindicated in pregnancy (can induce uterine contraction in pregnant women)

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12
Q

Stimulant laxative agents? (3)

A

Stimulate bowel activity
The MOST POTENT class of laxatives
1. Bisacodyl (a diphenylmethane) (synthetic)
2. Anthraquinones (natural)→Senna and Cascara Sagrade Extract

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13
Q

MoA of Stimulant laxatives? (5)

A

Stimulate bowel activities

a. Predominantly act on the large bowel (colon)
b. Increase the permeability of intestinal mucosa
c. Increase back diffusion (leakiness) of water and electrolytes
d. Increase propulsive contractility of the colon stimulating colonic myenteric plexus (more rapid transit=less time for absorption)
e. Stimulate PG synthesis and increase intestinal secretions

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14
Q

Characteristics and ADEs of Bisacodyl (diphenylmethane)?

A

a. Characteristics:
1. Prodrug converted by enteric bacteria into desacetyl active form.
2. Administered in enteric-coated tablet (doesn’t dissolve til colon)
b. ADEs: overdosing can cause:
1. Excessive fluid and electrolyte loss (drink fluids)
2. Intestinal enterocyte damage leading to colonic inflammatory response

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15
Q

Characteristics and ADEs of the Natural stimulant laxative anthraquinones→Senna and Cascara Sagrade Extract?

A 
Characteristics:
1. Natural derivatives of Lilliaceae plants
2. More gentle than synthetic stimulants
3. Act by promoting colonic motility
ADEs: Large doses can cause:
1. Abdominal pain
2. Nephritis
3. Melanotic pigmentation of colonic mucosa/stool (not blood)
4. Abnromal urine coloration
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16
Q

What are Osmotic (and saline) Laxatives?

A

Laxatives containing magnesium cations or other non-absorbable molecules. They exert an osmotic effect which retains water in the GI tract lumen.

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17
Q

What are the types of osmotic laxatives? (3 classes, 7 total)

A

A. Magnesium-containing laxatives
1. Mg Sulfate 2. Mg Hydroxide 3. Mg Citrate (cathartic)
B. Phosphate-containing→Buffered Phosphate
C. Non-digestible Sugars and Alcohols
1. Lactulose
2. Glycerin
3. Polyethylene Glycol (PEG) Electrolyte Solution

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18
Q

MoA of Mg-containing laxatives?

A

a. Osmotic effect (draws water into lumen)

b. Cause release of CCK→increases intestinal motility and secretion

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19
Q

How is Buffered Phosphate given?

A

Given as a fleet enema (to the colon via the anus) or as oral sodium phosphate tablets

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20
Q

Actions of Lactulose? (2)

A

Lactulose is a non-absorbable semisynthetic disaccharide:

  1. Osmotic effect→non-absorbable→draws water into lumen
  2. Fecal Acidifier→metabolized by enteric bacteria to organic acids (lactic, formic, and acetic acid)→acidification traps ammonia in the ammonium form which is not toxic
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21
Q

Glycerin effects? (2)

A

Given as suppository; has osmotic and lubricant (eases passage) effects

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22
Q

Can PEG be used for colonoscopy prep?

A

Yes, b/c it can cause complete evacuation

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23
Q

Two Miscellaneous laxative agents? Effects?

A
  1. Haley’s Mineral Oil→a mixture of hydrocarbons that penetrates and softens stool
  2. Castor Oil→an emulsion that irritates mucosa and produces a cathartic effect
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24
Q

Two agents used in treatment of constipation-predominant IBS (IBS-C)

A
  1. Lubiprostone→targets the chloride channel

2. Linaclotide→targets gaunylate cyclase

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25
Q

MoA and effect of Lubiprostone?

A

Specifically activates intestinal Cl- channels in a PKA-dependent fashion.
Cl channel activation→increased intestinal fluid secretion and motility
This alleviates the symptoms associated w/ chronic idiopathic constipation

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26
Q

MoA of Linaclotide?

A

Peptide agonist of Guanylat Cyclase-2C→increased cGMP→indirect activation of the Cl- channel.

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27
Q

What is Laxative Abuse?

A

a. Laxative abuse is constipation that requires several days to accumulate bulk.
b. Lag in defecation is interpreted as continued constipation
c. Take more laxatives→vicious cycle
d. If continued, bowel becomes unresponsive

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28
Q

3 Groups of Anti-diarrheal Agents?

A
  1. Agents that absorb water
  2. Adsorbers of etiological factors in the lumen
  3. Agents that alter intestinal motility
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29
Q

MoA and examples (2) of anti-diarrheal agents that absorb water?

A

MoA: Pull/draw water and swell, producing more formed stool.
Examples: Cellulose derivatives, Semisynthetic polysaccharides

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30
Q

Examples (2) and MoA of anti-diarrheals that adsorb etiologic factors in the GI lumen?

A
  1. Bismuth Subsalicylate
  2. Charcoal
    MoA: adsorb harmful bacteria, viruses, or toxin
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31
Q

Bismuth subsalicylate is effective in prevention/treatment of what? (2)

A

a. Prevention of traveler’s diarrhea (ie in Mexico)

b. Treatment of H. pylori infections (bacteriostatic effects)

32
Q

What two drug classes of anti-diarrheals alter intestinal motility?

A
  1. Opiates

2. Anticholinergics

33
Q

MoA/effects (5) of Opiates in Rx of diarrhea? Net Result of Opiates?

A
  1. Decrease salivary, gastric, and intestinal secretions
  2. Decrease motility of stomach and intestines
  3. Increase muscle tone
  4. Increase the tone of intestinal sphincters, inclduding the external anal sphincter→REDUCED URGENCY
  5. They are anti-spasmodics that decrease cramps
    Net Result = opiates INCREASE THE CONTACT TIME b/t ingested matter and the absorptive intestinal epithelium
34
Q

Opioid agents specifically formulated for diarrhea? (3)

A
  1. Paregoric
  2. Diphenoxylate w/ Atropine
  3. Loperamide
35
Q

Why Diphenoxylate+Atropine combination?

A

Atropine prevents abuse by reducing the tolerable dose

36
Q

MoA of Loperamide? (2)

A
  1. Interacts with opioid receptors

2. binds to and inhibits the Ca-binding protein Calmodulin

37
Q

MoA and and main effect of Anti-cholinergics in the Rx of diarrhea?

A

MoA: block cholinergic receptors and reduce vagal (Ach) stimulation
Mainly used for diarrhea b/c of their anti-spasmodic effect which alleviates cramps.

38
Q

Anticholinergic agents used in Rx of diarrhea? (2) What is special about their structure?

A
  1. Propantheline
  2. Dicyclomine
    These are quarternary ammonium derivatives of atropine so they cannot cross BBB and have minimal side effects.
39
Q

How do the 2 anticholinergic agents compare?

A

a. Dicyclomine is more suited to alleviate cramps in diarrhea
b. Propantheline is frequently used for urinary retention

40
Q

Emetic agent used to induce vomiting? MoA?

A

Tincture of Ipecac (Emetine)→acts on medullary vomiting center (VC) to induce vomiting

41
Q

Anti-emetic Agents (5 Classes) used in the Rx of N/V?

A
  1. Anticholinergics: Scopolamine
  2. H1 Antihistamines (antagonists)
  3. Antidopaminergics
  4. Serotonin Antagonists
  5. Miscellaneous→Dronabinol, Corticosteroids, Aprepitant, Benzodiazepine
42
Q

Which two anti-emetic classes are used in the Rx of Motion Sickness?

A
  1. Scopolamine

2. H1 Antihistamines

43
Q

MoA of Scopolamine?

A

Antimuscarinic:
Cochlear sensation of motion is projected via cholinergic fibers of the auditory nerve (CN 8) to the chemoreceptor trigger zone (CTZ). Scopolamine is an anticholinergic that blocks the activation of these Muscarinic 1 (M1) receptors by Ach.

44
Q

Use of Scopolamine? ADEs?

A

Prophylactic only→for motion sickness arising from exposure to severe motion (at sea)
ADE’s:
1. SEDATION
2. Extrapyramidal effects (drowsiness, dry mouth)

45
Q

H1 Antihistamine MoA? (2)

A
  1. Antihistamine effects (block H1-R’s in inner ear and CNS)

2. Anticholinergic effects (these are older antihistamines)

46
Q

H1 Antihistamine agents? (4)

A 
A. Ethanolamine derivatives
1. Dimenhydrinate
B. Piperazine derivatives
1. Cyclizine   2. Meclizine
C. Phenothiazine derivatives
1. Promethazine
Read slide about specifics
47
Q

Which H1 antihistamine is used for vestibular disturbances (Vertigo, Menier’s)?

A

Meclizine

48
Q

Side effect of Promethazine?

A

Sedation

49
Q

What is the major type of signaling in the Chemoreceptor Trigger Zone (CTZ) involved in emesis?

A

Dopaminergic signaling via D2 receptors

50
Q

MoA of Anti-dopaminergics as anti-emetic agents?

A

Block D2-R’s in the CTZ

51
Q

Anti-dopaminergic agents used in Rx of N/V? (6)

A 
A. Phenothiazines
1. Chlorpromazine
2. Prochlorperazine
3. Thiethylperazine
B. Butyrophenone derivatives
1. Droperidol
C. Benzamide derivatives
1. Metoclopramide
2. Trimethobenzamide
52
Q

What are the phenothiazine anti-dopaminergics? (3)

A
  1. Chlorpromazine
  2. Prochlorperazine
  3. Thiethylperazine
53
Q

MoA of Chlorpromazine (2)? Clinical uses?

A 
Centrally acting:
1. Antimuscarinic (M1)
2. Antidopaminergic (D2)
Clinical uses: 
a. N/V
b. Intractable hiccough (hiccups)
54
Q

MoA of Thiethylperazine? (2)

A

Inhibits both CTZ and VC

55
Q

MoA and clinical use of Droperidol?

A

MoA: blocks D2-R’s in CTZ.

Clinically used post-operatively for N/V

56
Q

MoA (2) and clinical uses (2) of Metoclopramide as an anti-emetic agent?

A

MoA:
1. D2 antagonist that blocks chemotherapy-induced activation of D2-R’s in CTZ.
2. Stimulates gastric emptying (less gastric contents to vomit up)
Clinical Use: given prophylactically prior to cancer chemotherapy and in prevention of postoperative N/V.

57
Q

ADEs of Anti-dopaminergics?

A

Extrapyramidal effects→therefore, only for short-term use

58
Q

Anti-emetic Serotonin antagonist agents? (4)

A

the “-SETRON’s”
1. Ondansetron
2. Granisetron
3. Dolasetron
4. Palonosetron
These are the MOST EFFECTIVE anti-emetics currently available

59
Q

MoA of Serotonin (5HT) Antagonists as anti-emetics?

A
  1. Block 5HT3-R’s in stomach and small intestines. (Stomach/S.I. transmit their stimuli thru vagal and sympathetic afferents to the CTZ and VC thru the solitary tract nucleus.)
  2. Block 5HT3-R’s in CTZ that are intimately involved in stimulating the VC to produce emesis.
60
Q

How are serotonin antagonists used in anti-emetic therapy?

A

Alone or in combination with other drugs, such as glucocorticoids and benzodiazepines

61
Q

Describe Ondansetron?

A

a. A selective 5HT3 blocker

b. Effective in preventing emesis by high-dose cytotoxic drugs such as Cisplatinum/radiation

62
Q

Which serotonin antagonist is more potent than Ondansetron?

A

Granisetron

63
Q

Which 5HT3 blocker has the longest half-life?

A

Dolasetron

64
Q

Concurrent use of what drug with 5HT3 blockers significantly increases their potency?

A

Dexamethasone (glucocorticoid)

65
Q

What are miscellaneous anti-emetic drugs given?

A

Agents given with aforementioned anti-emetics to: 1. Increase their potency

  1. Reduce the dose of each individual agent
  2. Reduce their combined side effects
66
Q

What are the 4 miscellaneous agents used in anti-emetic treatment?

A
  1. Dronabinol
  2. Corticosteroids
  3. Aprepitant
  4. Benzodiazepines
67
Q

MoA of Dronabinol?

A

A major active substance in marijuana that stimulates the CB1-R subtype of cannabinoid receptors

68
Q

Indication and ADE of Dronabinol?

A

Principally used as an anti-emetic in cancer chemotherapy ONLY when pt’s have failed to respond to other anti-emetics
ADE: Psychomimetic reactions not induced with other anti-emetics (monitor carefully)

69
Q

Which two corticosteroids are used as anti-emetics?

A
  1. Dexamethasone

2. Methyl prednisolone

70
Q

MoA and Clinical Use of corticosteroids?

A

Clinical Use: they enhance the overall effect and reduce side effects when combined w/ other anti-emetics
MoA: inhibit PG production associated w/ chemo or radiation therapies

71
Q

MoA and Clinical Use of Aprepitant?

A

MoA: Substance P/Neurokinin 1 (NK1) receptor antagonist that crosses the BBB and inhibits emesis via central actions.
Clinical Use: As an adjunct drug for preventing emesis induced by cytotoxic chemotherapy drugs such as Cisplatin.

72
Q

Pharmacokinetics of Aprepitant? (3)

A
  1. t1/2 = 9-13h
  2. Tmax reached w/in 4h orally
  3. Completely metabolized by hepatic CYP3A4
73
Q

Which two benzodiazepines are used as anti-emetics?

A
  1. Lorazepam

2. Alprazolam

74
Q

Clinical use of benzodiazepines?

A

As an adjunct to other anti-emetics.
They are effective in pt’s w/anticipatory vomiting b/c they cause somnolence/amnesia lasting for hours. Given one day prior to initiation of chemotherapy.

75
Q

Anti-emetic regimen in cancer chemotherapy?

A

5HT3 antagonist with miscellaneous anti-emetics added as required to achieve high efficacy

GI Pharm (7 decks)

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