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Gastrointestinal Pharmacology Flashcards

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1
Q

What are the three common proton pump inhibitors and their indications.

A

Omeprazole

Lanzoprazole

Pantoprazole

Indications;

  • prevention and treatment of PUD
  • Symptomatic relief of dyspepsia and GORD
  • Eradication of H. Pylori
    • in conjunction with antibiotics such as amoxicillin, metronidazole, clarithromycin: OCA or OCM
  • Less common- Zollinger-Ellison syndrome (a gastrinoma: often pancreatic- non B-cell)
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2
Q

What is the mechanism of action of PPIs

A

Irreversible inhibition by covalent modification of the gastric gland parietal cell H+/K+-ATPase (the proton pump) present in the apical (canalicular membrane)

PPIs are produgs which are acticated in the acidic environment of the canaliculus, contributing to their effectiveness and selectivity of action.

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3
Q

What are the warnings and adverse effects or PPIs

A

Generally safe

  • diarrhoea (lanzoprazole)
  • Headache
  • Abdominal Pain
  • Nausea
  • Fatigue
  • Dizziness
  • Some evidence for increased risk of C.Diff infection
  • Prolonged use: rebound acid hypersecretion upon discontinuation

Warnings

  • may disguise symptoms of gastric cancer
  • in elderly, increased risk of bone fracture
  • Interactions with cytochrome P450 decreases the antiplatelet activity of clopidogrel and increases the effect of phenytoin and warfarin
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4
Q

What is the administration of PPIs

A
  • PO once daily or IV
  • PO best taken in the morning before food
  • IV (by slow injection or infusion)- to treat recurrent ulcer bleeding in high risk patients)
  • Low omeprazole dose is available OTC
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5
Q

What are three specific Histamine Type 2 receptor antagonists?

A
  • Ranitidine
  • Famotidine
  • Nizatidine
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6
Q

What is the mechanism of action of H2 receptor antagonists?

A

Competitive antagonism of the H2 receptor located on the basolateral membrane of acid secreting parietal cells of the gastric glands.

Histamine released from nearby eterochromaffin-like (ECL) cells of the gastric mucosa acts in a paracrine matter to increase the activity of the H+ /K+-ATPase of the parietal cells by increasing the intracellular concentration of cAMP which, via protein kinase A, promotes the trafficking of the H+ /K+-ATPase to the canalicilar mebrane.

It thus reduces gastric acid production but since other stimuli (e.g. ACh and gastrin) are still capable of directly stimulating the parietal cell via their respective receptors, they are less effective than PPIs

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7
Q

What are the two major indications of H2 receptor antagonists?

A
  1. prevention and treatment of PUD
  2. Symptomatic relief of dyspepsia (may be sufficient) and GORD
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8
Q

What are the adverse effects of H2 receptor antagonists?

A

Generally very safe, side effect profile superior to PPIs

  • bowel disturbance
  • headache
  • abdominal pain
  • dizziness
  • Cimetidine- Has anti-adrogenic effects (gynaecomastia and impotence) and may potentiate the anti-coagulant activity of warfarin
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9
Q

What is a major caution of H2 receptor antagonists?

A

It may disguise symptoms of gastric cancer

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10
Q

What is the dosing of H2 receptor antagonists?

A

PO (twice daily)
Evening dose important due to decreased buffering of gastric pH during fasting period.

Ranitidine is available OTC as low dose (150-300mg) preparations

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11
Q

When would you adjust the dosage of H2 receptor antagonists?

A

In moderate to severe renal impairment

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12
Q

What is the best choice for supression of acid secretion pre-operatively?

A

H2 receptor antagonists due to their rapid onset of action.

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13
Q

What are two common antimotility drugs?

A

Loperamide

Codeine Phosphate

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14
Q

What is the mechanism of action of Loperamide?

A

It is a synthetic opioid with agonist activity at u opioid receptors expressed by enteric neurons of the GI tract.

It increases the tone and rhythmic contractions of the intestine, constricts smooth muscle sphincters, but inhibits peristalsis.

It has additional antisecretory activity

‘era weenteric bit of opioid’

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15
Q

What is the mechanism of action of Codeine phosphate?

A

Similar to loperamide

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16
Q

What is the preferred antimotility drug?

A

Loperamide due to little CNS action

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17
Q

What are the major indications of antimotility drugs?

A
  1. Treatment of acute diarrhoea for symptomatic relied (usually in the context of gastritis caused by viral, or bacterial, infections)
  2. Symptomatic relief of diarrhoea associated with IBS
  3. Analgesia for acuter moderate pain (codeine)
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18
Q

What are the adverse effects of antimotility drugs?

A
  • constipation
  • abdominal cramping
  • flatulence
  • inappropriate inhibition of peristalsis may trigger serious conditions
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19
Q

What are the contraindications of antimotility drugs?

A
  • Acute ulcerative colitis (risk of megacolon and perforation)
  • Acute bloody diarrhoea (dysentry)
  • C.diff colitis
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20
Q

What are the warnings associated with antimotility drugs?

A
  • DO NOT give to patients with diarrhoea that develops in hospital settings until the probable cause is identified, and C.diff has been excluded
  • SHOULD NOT be used in children under 4
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21
Q

What is the administration of antimotility drugs?

A

PO as capsule, or tablet.

Loperamide low dose (2mg) is available OTC

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22
Q

What are three bulk forming laxatives?

A
  • Ispagula husk
  • methylcellulose
  • sterculia
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23
Q

What is the mechanism of action of bulk forming laxatives?

A
  • hydrophillic agents such as a polysaccharide or cellulose- indigestible
  • By osmosis- water is attracted to the stool, increasing bulk and stimulating peristalsis
  • Adequate fluid ingestion is imperative
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24
Q

What are the two major indications of bulk forming laxatives?

A
  1. constipation and faecal impaction. Gastritis caused by viral, or bacterial infection.
  2. Mild chronic diarrhoea associated with diverticular disease, or IBS
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25
What are the adverse effects of bulk forming laxatives?
* Abdominal distension * flatulence * rarely may cause faecal impaction and gastrointestinal obstruction
26
What are the contraindications of bulk forming laxatives?
Intestinal obstruction Ileus
27
What is the administration of bulk forming laxatives?
PO (as powders, granules, tablets) Around meal time and drink plenty of water Available OTC
28
What are four osmotic laxatives?
* lactulose * macrogols * citrate * phosphate enemas
29
What is the mechanism of action of osmotic laxatives?
Osmotically active agents (sugars, alcohols) that are neither digested, nor absorbed. By osmosis water is attracted to the stool, increasing bulk and stimulating peristalsis. Lactulose which is relatively slow to act reduces ammonia absorption by decreasing transmit time, acidifying the stool and inhibiting the proliferation of ammonia producing bacteria which is helpful in patients with liver failure. Rectal administration of phosphate enemas cause rapid bowel evacuation.
30
What are the three main indications of osmotic laxatives?
1. constipation and faecal impaction 2. bowel preparation 3. hepatic encephalopathy
31
What is the contraindication of osmotic laxatives?
Intestinal obstruction
32
What are the adverse effects of osmotic laxatives?
* abdominal cramps * diarrhoea * phosphate enemas cause local irritation and electrolyte disturbances
33
What are the warnings associated with osmotic laxatives?
Phosphate enemas may cause significant fluid shifts and should be used with causing in **heart failure** or when electrolyte disturbances are present.
34
What is the administration of osmotic laxatives?
PO (as powders dissolves in water, or as liquids) with, or without food. As enema, once only are as required but no more than once daily. Osmotic laxatives are available OTC
35
What is the first line treatment for faecal impaction?
A glycerol suppository (stimulant laxative) should be tried before a phosphate enema
36
What are four stimulant laxatives?
* Senna * Bisocodyl * Glycerol suppository * Docusate sodium
37
What is the mechanism of action of stimulant laxatives?
**Increase water** and **electrolyte secretion** from **colonic mucosa.** **Colonic content is increased** **stimulating peristalsis**, which may also occur by a **direct action** of the **enteric nervous system.** **Docusate sodium** has additional **faecal softening** action
38
What are the major indications for stimulant laxatives?
1. constipation 2. faecal impaction
39
What are the adverse effects of stimulant laxatives?
* abdominal pain * cramping * diarrhoea * Phosphate enemase cause irritation and electrolyte imbalances * Prolonged use causes irreversible atonic colon and reversible melanosis coli
40
What are the contraindications of stimulant laxatives?
Intestinal obstruction Risk of perforation
41
What are the warnings associated with stimulant laxatives?
rectal preparations should be avoided when anal fissures or haemorrhoids are present
42
What is the administration for Stimulant laxatives?
For constipation= PO For faecal impaction= As suppository Available OTC
43
When may stimulant laxatives by routinely prescribed?
To patients taking regular opioid analgesics
44
What is the mechanism of action of dopamine D2 receptor antagonists?
**Domperidone** is an antagonist of dopamine D2 receptors. Unlike **metoclopramide** which possesses additional antagonist activity at 5-HT3 and agonist activity at 5-HT4 receptors. **Domperidone does not cross the BBB.** D2 receptors are commonly expressed in the chemoreceptor trigger zone (CTZ) that lies outside the BBB. In the G.I. tract dopamine relaxes the stomach and lower oesophageal spincters and disrupts gastroduodenal coordination.
45
What are the major indications of D2 receptor antagonists?
1. treatment of nausea and vomitting in a wide range of conditions, but particularly when reduced gut motility is evident. **Domperidone** is used in drug/chemotherapy-induced nausea and vomiting 2. Treatment of GORD as add on in patients who do not respond to PPIs or H2 receptor antagonists
46
What is a rare indication of D2 receptor antagonists
Vomitting associated with emergency contraception
47
What are the adverse effects of D2 receptor antagonists?
* diarrhoea * **metoclopramide-** may cause movement disorders, motor restlessness, spasmodic torticollis, and oculogyric crisis
48
What are the contraindications of D2 receptor antagonists?
GI obstruction and perforation
49
What are the warnings associated with metoclopramide?
Best avoided in young children and yound adults whre extrapyrimidial effects are most common
50
What is the administration for D2 receptor antagonists?
PO up to three times daily Metoclopramide, but not domperidone is available for IM or IV injection
51
What are some H1 receptor antagonists?
Cyclizine Cinnarazine Promethazine
52
What is the mechanism of action of H1 receptor antagonists?
Competitive antagonism of H1 receptors in the vomitting centre and elsewhere in the CNS (*causing sedation*) Additional block of muscarinic (M1) ACh receptors in the vestibular apparatus probably contributes to their effectiveness
53
What is the major indication for H1 receptor antagonist?
Treatment of nausea and vomiting in a wide range of conditions, particularly motion sickness and vertigo. Post-operative nausea and vomiting. Less effective in treating nausea and emesis caused by agents that stimulate the chemoreceptor trigger zone directly
54
What are the adverse effects of H1 receptor antagonists?
Most commonly **drowsiness** and **sedation** (but drowsiness may contribute to clinical effect as newer agents that are less sedative have reduced antiemetic action). Cyclizine is least likely to cause sedation. Due to their **anti-cholinergic** action these agents may **reduce saliva secretion** causing a **dry mouth**. If administered IV they may cause a **transient tachycardia**
55
What are the warnings and cautions associated with H1 receptor antagonists?
Should be avoided in patients at risk of hepatic encephalopathy, or those with prostatic hyperplasia (antimuscarinic action increases the likelihood of urinary obstruction)
56
What is the administration of H1 receptor antagonists?
PO regularly, or as required. **Cyclizine** may be given IM, or IV (*e.g. in vomiting patients)* in the latter case by slow IV injection. IV administration is associated with unpleasant sensations (e.g. palpitations)
57
What are two examples of Phenothiazines?
Procloperazine Chloropromazine
58
What is the mechanism of action of Phenothiazines
Complex. Involves the competitive antagonism of dopamine D2, histamine H1 and muscarinic M1 receptors on the vomiting centre, vestibular system and peripherally in the gut
59
What are the major indications of Phenothiazines?
1. Treatment of nausea and vomitting in a wide range of conditions, particularly vertigo and sometimes chemotherapy induced nausea and vomitting 2. Psychiatric disorders (*e.g. schizophrenia)*
60
What are the adverse effects of phenothiazines?
Most commonly drowsiness and postural hypotension Extrapyrimidial symptoms Long term treatment= tardive dyskinesia or parkinsonism QT interval prolongation may occur, which is a class effect of antipsychotics
61
What is the contraindication for phenothiazines?
Avoid in severe liver disease
62
What is the administration of phenothiazines?
Orally, or deep IM, for acute episode with further oral doses as necessary
63
What are three 5-HT3 receptor antagonists?
Odansetron Granisetron Palonosetron
64
What is the mechanism of action of 5-HT3 receptor antagonists?
Competitive antagonism of inotropic 5-HT3 receptors. Located in the CTZ, nucleus tractus solitarus, and also peripherally on the terminals of vagal afferent fibres innervating the GI tract. They are ineffective in the treatment of motion sickness.
65
What are the major indications of 5-HT3 receptor antagonists?
1. Treatment of nausea and vomitting associated with chemo and radiotherapy 2. Following surgery involving the use og general anaesthetic agent
66
What are the uncommon indications of 5-HT3 receptor antagonists?
1. IBS (*diarrhoea predominant in female patients, for which alosetron is used*) 2. Hyperemesis gracidarum- use of odansetron is not licensed
67
What are the adverse effects of 5-HT3 receptor antagonists
Constipation Diarrhoea Headaches
68
What are the contraindications for 5-HT3 receptor antagonists?
* Severe or prolonged constipation * Intestinal obstruction * strictire * toxic megacolon * ischaemic colitis * chron's disease * ulcerative colitis * diverticulitis
69
What are the warnings and cautions associated with 5-HT3 receptor antagonists?
High dose **odensetron** maybe associated with a prolonged QT interval
70
What is the administration for 5-HT3 receptor antagonists
PO, PT, IM or IV ## Footnote *Dependant on clinical situation.*

Pharmacology (4 decks)

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