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Drug Formulary Y3 > Gastrointestinal Drugs > Flashcards

Gastrointestinal Drugs Flashcards

1
Q

What type of drug is Gaviscon and Peptac?

A

They both fall under ‘antacids & alginates’

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2
Q

How do the combination of antacids and alginates work?

A

Antacids work by buffering stomach acids, while alginates increase the viscosity. They react with stomach acid and form a floating raft, separating the gastric contents from the gastro-oesophageal junction.

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3
Q

What are the indication for use of antacids/alginates? (2)

A
  1. GORD - symptomatic relief of heartburn

2. Dyspepsia - symptomatic relief of indigestion

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4
Q

What are the contra-indications for using alginates/antacids?

A
  1. In combination with thickened milk preparations in infants
  2. In patients with renal failure; Na+ and K+ containing preparations should be used with caution
  3. People with diabetes should avoid sucrose containing preparations
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5
Q

What are the possible side effects of using antacids/alginates? (3)

A
  1. Nausea
  2. Constipation/Diarrhoea
  3. Headache
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6
Q

In what way can alginates reduce the absorption of other drugs?

A

The divalent cations in compound alginates can bind to other drugs

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7
Q

Why should antacids be taken at different times to other drugs?

A

They can reduce serum concentrations of many drugs, this applies to: ACE inhibitors, antibiotics (cephalosporins, ciprofloxacin and tetracyclines), bisphosphonates, digoxin, levothyroxine and PPIs.
They can also increase excretion of aspirin and lithium.

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8
Q

How long does it take for antacid/alginate compounds to work?

A

Symptoms should be relieved within 20 minutes - hours.

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9
Q

Name a H2-receptor antagonist?

A

Ranitidine
Cimetidine
Nizatidine

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10
Q

What is the mechanism of action of H2-receptor antagonists?

A

Histamine (H2) receptor antagonists reduce gastric acid secretion. Histamine regulates the proton pump, secreting gastric acid into the stomach lumen, so by blocking the histamine receptor, gastric acid secretion is suppressed. Histamine however is not the only regulator, so some gastric acid will still be secreted.

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11
Q

If PPIs are better at suppressing gastric acid secretion, why are H2-antagonist receptors still prescribed?

A

H2-receptor antagonists have a more rapid onset, so can be useful in certain situations, for example pre-operatively.

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12
Q

What are the indications for use of H2-receptor antagonists? (2)

A
  1. Peptic ulcer disease - for treatment and prevention (PPIs are usually first line though)
  2. GORD/dyspepsia - for relief of symptoms (once again PPIs are generally preferred)
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13
Q

When would you need to give a reduced dose of H2-receptor antagonists? (1)

A

In patients with renal impairment

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14
Q

What could using H2-receptor antagonists mask the worrying symptoms of?

A

Gastric cancer - they can disguise the symptoms, therefore care needs to be taken and investigations carried out if there are suspicions

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15
Q

Are there any side effects of using H2-receptor antagonists?

A

Generally well tolerated, however most common side effects include bowel disturbances (diarrhoea/constipation), headaches and dizziness.

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16
Q

What are the possible interactions when using H2-receptor antagonists?

A

There are no major drug interactions

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17
Q

How are H2-receptor antagonists eliminated from the body?

A

Excreted via the kidneys

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18
Q

Name 3 common proton pump inhibitors?

A
  1. Omeprazole (oldest one)
  2. Lansoprazole (most commonly prescribed)
  3. Pantoprazole
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19
Q

What is the mechanism of action of PPIs?

A

They irreversibly inhibit H+/K+-ATPase in gastric parietal cells (aka proton pump). As they target the final stages of gastric acid secretion, they suppress acid secretion almost entirely.

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20
Q

What are the indications for use of a PPI? (3)

A
  1. Peptic ulcer disease - first-line in prevention and treatment, including for NSAID induced ulcers.
  2. GORD/dyspepsia
  3. Helicobacter pylori infection - used in combination with antibiotic therapy
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21
Q

What is the contra-indication for use of a PPI? (1)

A

Patients at risk of osteoporosis should be identified and not treated with PPI’s for long periods of time, as they can increase the risk of fractures

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22
Q

What are the common side effects of using PPIs?

What other side effects can occur?

A 
Commonly:
GI disturbances
Headaches 
Others:
Hypomagnesaemia --> which can lead to tetany/ventricular arrhythmia
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23
Q

Why is there evidence of increased C.diff infections when using PPIs?

A

PPIs increase the gastric pH, so the body may be less effective at tackling infection.

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24
Q

What are the possible drug interactions when using PPIs?

A

Evidence suggests PPIs, in particular, Omeprazole, reduce the anti-platelet effect of Clopidogrel, by decreasing its activation by cytochrome P450 enzymes. Thus when prescribing PPIs alongside Clopidogrel, Lansoprazole/Pantoprazole are preferred.

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25
Q

How are PPIs eliminated?

A

Via the kidneys

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26
Q

Name 2 antimotility (anti-diarrhoeal) agents?

A
  1. Loperamide

2. Codeine phosphate

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27
Q

How does loperamide work?

A

Loperamide is an opioid that is pharmacologically similar to pethidine, however does not penetrate the CNS, so has no analgesic effects. Its action is to increase the non-propulsive contractions of the gut smooth muscle, but reduce propulsive (peristaltic) contractions. As a result, transit of bowel contents is slowed and anal sphincter tone is increased. Slower gut transit allows for more water reabsorption, so the stool hardens.

28
Q

What are the indications for use of Loperamide?

A

Diarrhoea

29
Q

When should Loperamide not be prescribed? (2)

A

Should be avoided in acute ulcerative colitis, where inhibition of peristalsis could result in perforation.
Should also be avoided in people whose diarrhoea has been caused by broad spectrum antibiotic use (C.diff colitis).

30
Q

Are there any side effects of using Loperamide?

A

Very few, occasionally constipation, flatulence and abdominal cramps.

31
Q

Are there any drug interactions when using Loperamide?

A

None of which are clinically significant

32
Q

What vague safety warning regarding anti motility drugs was released by the BNF in September 2017?

A

Abuse/misuse of this drug can result in serious cardiac adverse reactions.

33
Q

Name 3 types of stimulant laxatives?

A
  1. Senna bisacodyl
  2. Glycerol suppositories
  3. Docusate sodium
34
Q

What is the mechanism of action for stimulant laxatives? (2)

A

They increase water and electrolyte secretion from the colonic mucosa, thereby increasing the volume of colonic content and stimulating peristalsis.
They also have a direct pro-peristaltic action, although the exact mechanism differs between agents

35
Q

What are the indications for use of stimulant laxatives? (2)

A
  1. Constipation

2. Faecal impaction - as suppositories

36
Q

What are the contra-indications for using a stimulant laxative?

A

If there is a risk of intestinal obstruction, as this could induce perforation.
Suppositories should be avoided in haemorrhoids or anal fissures are present.

37
Q

Name 3 types of osmotic laxatives?

A
  1. Lactulose
  2. Macrogol
  3. Phosphate enema
38
Q

What are the indications for using osmotic laxatives? (4)

A
  1. Constipation
  2. Faecal impaction
  3. Bowel preparation - prior to surgery or endoscopy
  4. Hepatic encephalopathy
39
Q

What is the mechanism of action of osmotic laxatives?

A

These medicines are based on osmotically active substances (sugars and alcohols) that are not digested or absorbed, and which therefore remain in the gut lumen. They hold water in the stool, maintaining its volume and stimulating peristalsis.

40
Q

Why is lactulose particularly useful for patients with liver failure?

A

Lactulose reduces ammonia absorption. It does this by increasing gut transit rate and acidifying stools, which inhibits proliferation of ammonia-producing bacteria. Ammonia plays a major role in the pathogenesis of hepatic encephalopathy.

41
Q

What are the contra-indications for using osmotic laxatives? (2)

A
  1. Intestinal obstruction

2. Heart failure, ascites and electrolyte disturbances - phosphate enemas can cause significant fluid shifts

42
Q

In a patient with faecal impaction, which type of laxative is used in first-line treatment?

A

Glycerol suppositories (stimulant). Although phosphate enemas (osmotic) can be used, they are an irritant and are more likely to cause electrolyte disturbances.

43
Q

What are the side effects of using laxatives of any kind?

A
  1. Abdominal cramps
  2. Flatulence
  3. Occasional diarrhoea
  4. Nausea
44
Q

Which 2 side effects can bulk-forming laxatives rarely cause that osmotic and stimulant laxatives don’t?

A
  1. Faecal impaction

2. GI obstruction

45
Q

Are there any drug interactions when using laxatives of any kind?

A

No

46
Q

Name 3 types of bulk-forming laxatives?

A
  1. Ispagula husk
  2. Methycellulose
  3. Sterculia
47
Q

What are the indications for using bulk-forming laxatives? (2)

A
  1. Constipation/faecal impaction - particularly in patients who cannot increase their dietary fibre intake
  2. Mild chronic diarrhoea - associated with diverticular disease or IBS
48
Q

What is the mechanism of action of bulk-forming laxatives?

A

Bulk-forming laxatives contain a hydrophilic substance, such as a polysaccharide or cellulose, which is not absorbed or broken down in the gut. Like dietary fibre, this attracts water into the stool and increases its mass. Adequate fluid intake is therefore important to the action of bulk-forming laxatives. Increased stool bulk stimulates peristalsis and helps to relieve constipation.

49
Q

What are the contra-indications for using bulk-forming laxatives? (similar to other laxatives)

A
  1. Subacute or established intestinal obstruction

2. Faecal impaction?!? - strange as it also states this as an indication for use?!

50
Q

What type of supplement are bulk-forming laxatives?

A

Fibre supplement

51
Q

Name 2 aminosalicylates?

A
  1. Mesalazine

2. Sulfasalazine

52
Q

What is Mesalazine a first-line treatment for?

A

In mild to moderate ulcerative colitis

53
Q

What is Sulfasalazine used to treat?

A

Rheumatoid arthritis - it is used as a disease modifying anti-rheumatic drug (DMARD)

54
Q

How do both mesalazine and sulfasalazine exert their therapeutic effects?

A

They both release 5-aminosalicylic acid (5-ASA). The precise mechanism of action of 5-ASA is unknown, but it has both an anti-inflammatory and immunosuppressive effect, and appears to act topically on the gut rather than systemically.

55
Q

What side effects can mesalazine cause? (2)

A
  1. GI upset (nausea, dyspepsia)

2. Headache

56
Q

What side effects can sulfasalazine cause?

A
  1. Reversible decrease in the number of sperm (oligospermia)

2. Serious hypersensitivity reaction comprising of fever, rash and liver abnormalities

57
Q

What rare but serious complications can be caused by aminosalicylates?

A

Both drugs can cause blood abnormalities e.g. leucopenia, thrombocytopenia and renal impairment

58
Q

What are the contra-indications for using aminosalicylates?

A

Patients who have aspirin sensitivity should not take these as salicylates are like aspirin

59
Q

What are the possible drug interactions to consider when prescribing mesalazine?

A

Mesalazine tablets with a pH sensitive coating (Asacol MR) may interact with drugs that alter gut pH. For example PPIs increase gastric pH so may cause the coating to be broken down prematurely.
Lactulose lowers stool pH and may prevent 5-ASA release in the colon.

60
Q

Name 2 anti-emetics (dopamine D2-receptor antagonists)

A
  1. Metoclopramide

2. Domperidone (champagne!)

61
Q

What is the indication of use for anti-emetics?

A

Nausea and vomiting

62
Q

How do anti-emetics work in the gut?

A

Dopamine D2-receptors are found in the gut and normally promote relaxation of the stomach and lower oesophageal sphincter. The process of blocking these receptors has a pro-kinetic effect. This means metoclopramide/domperidone promotes gastric emptying which contributes to an antiemetic action.

63
Q

How do antiemetic drugs work in the brain?

A

Dopamine D2-receptors are also found in the chemoreceptor trigger zone (CTZ) in the medulla. The CTZ is the area responsible for sensing emetogenic substances in the blood (e.g. drugs). If the D2-receptor is blocked then the CTZ will not sense the emetogenic substances.

64
Q

When should antiemetics not be used?

A

Should be avoided in children and young adults.

They are contraindicated in patients with GI obstruction and perforation.

65
Q

What are the side effects of using antiemetics?

A

Diarrhoea - most common
Metoclopramide can induce extrapyramidal syndromes (movement abnormalities) via the same mechanism as antipsychotics (as it crosses the blood-brain barrier, unlike domperidone).

66
Q

When is the risk of metoclopramide-incuded extrapyramidal side effects increased?

A

When it is prescribed alongside antipsychotics

67
Q

Which two drugs should metoclopramide not be prescribed alongside?

A
  1. Antipsychotics

2. Dopaminergic agents for Parkinson’s disease

Drug Formulary Y3 (9 decks)

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