GI Pharmacology Flashcards by Hannah Thomas

What are the three main areas of GI pharmacology?

Drugs that suppress gastric acid
Drugs that affect gut motility and secretions
Drug treatment for inflammatory bowel diseases
Laxatives

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What are the main two conditions that are treated by acid-suppressing drugs?

Acid reflux (GORD)
Peptic ulcer disease

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Give three classes of drugs for acid suppression

H2 antagonists
Proton pump inhibitors
Antacids

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How do H2 antagonists work?

Block the H2 (histamine) receptors
- histamine released from ECL cells in the stomach stimulates parietal cells to produce stomach acid, therefore blocking the H2 receptors decreases acid production

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Give four examples of H2 antagonists

Cimetidine
Famotidine
Nicatidine
Ranitidine

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How do PPIs work? Give an example of a PPI

Reduce the number of hydrogen ions (protons) that are pumped into the stomach lumen

this reduces the amount of stomach acid being produced
e. g. omeprazole

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How do antacids work?

Directly neutralise hydrogen ions in the stomach lumen

- some also coat the surface of the oesophagus to protect against stomach acid

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Give some common ingredients in antacids

aluminium hydroxide
magnesium carbonate
magnesium trisilicate

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What conditions/symptoms are treated by drugs that affect gut motility?

Vomiting
Abdominal pain
Diarrhoea
Constipation
Irritable bowel syndrome

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What do prokinetic agents do? What are they used to treat?

Increase gut motility and gastric emptying

Treat gastroparesis, GORD

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Give two examples of prokinetic agents and describe how they work

Metoclopramide, Domperidone
Dopamine antagonists
Involves parasympathetic nervous system control of smooth muscle and sphincter tone (via ACh)

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Give two examples of drugs that decrease gastric motility and describe how they work

Loperamide (immodium), Opiates
Work via opiate receptors in GI tract to decrease ACh release
Decrease smooth muscle contraction
Increase anal sphincter tone

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Which class of drugs can be useful in IBS? 
Give an example
Describe the various mechanisms involved

Anti-spasmodics, e.g. Buscopan
1. Anti-cholinergic muscarinic antagonists (hyoscine buscopan, mebeverine)
inhibit smooth muscle constriction in the gut wall, producing muscle relaxation and reduction spasm.
2. Direct smooth muscle relaxants
3. Calcium-channel blockers (peppermint oil) reduce calcium required for smooth muscle contraction

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Describe the effect of fibre on stool constistency

Increase fibre to treat constipation

Decrease fibre to treat diarrhoea

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Describe how laxatives work and give four types (and an example for each type)

Either by increasing bulk of faeces or by drawing fluid into the gut

Bulk e.g. Isphagula
Osmotic e.g. Lactulose
Stimulant e.g. Senna
Softeners e.g. Arachis oil

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Describe the potential issues with laxative use

Do not give if there may be an obstruction
Consider lifestyle changes first
Route of administration: oral or rectal
Need for other measures, e.g. osmotic laxatives require adequate fluid intake in order to work
Ensure patient is actually in need of them
Misuse

What classes of drugs are used to treat inflammatory bowel disease?

Aminosalicyclates
Corticosteroids
Immunosuppressants
Biologics

Describe the use of aminosalicyclates in treating IBD

Anti-inflammatory
Metabolised in the liver
Oral or rectal administration

Give two examples of aminosalicyclates

Mesalazine, Olsalazine

Describe the side-effects and potential adverse effects related to aminosalicyclates

Nausea is common
Potential to cause GI upset, blood dyscrasia, renal impairment
Chemically similar to salicyclates which some patients are allergic to - must be avoided if this is the case
Use with caution (or not at all) in patients with pre-existing renal impairment

Describe the use to corticosteroids in treating IBD

Anti-inflammatory
Given orally, IV or rectally
Often used to settle acute attacks

Why must you be cautious with long term use of steroids?

Risk of Addisonian crisis if steroids are withdrawn too abruptly

Describe the concerns/contraindications associated with steroid use

Osteoporosis
Cushingoid features including weight gain, DM, HT
Increased susceptibility to infection
Addisonian crisis with abrupt withdrawal

Describe the use of immunosuppressants in the treatment of IBD and give an example

E.g. Azathioprine
Prevents the formation of purines required for DNA synthesis, so reduces immune cell proliferation
Good for when reducing dose of steroids

What are the risks associated with using immunosuppressants?

Adverse effects: bone marrow suppression, azathioprine hypersensitivity, organ damage Numerous drug interactions

Which organs are most at risk of being damaged by immunosuppressant use?

Lung Liver Pancreas

What are biologics and what are they used for? Give an example

Anti-TNFa antibodies E.g. infliximab Mouse-human chimeric antibody to TNFa Used to treat IBD, psoriasis and rheumatoid arthritis

How to biologics work?

Prevents action of TNFa, a key cytokine in inflammatory response Addresses inflammatory response but not underlying disease processes

Give three contraindications for infliximab

Current TB or other serious infection Multiple sclerosis Pregnancy/breast feeding

What are the potential adverse effects of Infliximab?

``` Risk of infection, particularly TB Infusion reaction - fever, itch Anaemia, thrombocytopenia, neutropenia Malignancy Possible demyelination ```

Give five other examples of biologics (aside from infliximab)

``` Certolizumab Adalimumab Natalizumab Golimumab Vedolizumab ```

Give two drugs that affect biliary secretions

Cholestyramine - reduces bilirubin | Ursodeoxycholic Acid - dissolves/prevents gallstones

Describe the effects of cholestyramine

Used to treat pruritis from biliary cause Reduces bile salts by binding with them in the gut and hen excreting as an insoluble complex May affect absorption of other drugs - must be taken separately May affect soluble vitamin absorption so may decrease vitamin K level - this affects clotting so must be careful if a patient is also on warfarin

Describe the uses/effects of ursodeoxycholic acid

used to treat gallstones and primary biliary cirrhosis inhibits an enzyme involved in the formation of cholesterol, altering amount in bile and slowly dissolving non-calcified stones

Define pharmacodynamics

How a drug affects an organism

Define pharmacokinetics

How an organism affects a drug

What are the main effects of antibiotic-induced changes to the gut flora?

Loss of oral contraceptive pill (OCP) activity Reduced vitamin K absorption (increased prothrombin time) Overgrowth of pathogenic bacteria (e.g. Clostridium difficile)

Which scoring system is used to classify prognosis in chronic liver disease and cirrhosis? What is its role in prescribing?

Child-Pugh score Classify patients as high or low risk (Class A, B, C) Helps to decide strength of treatment needed and extend of effect on ADME of other drugs (particularly warfarin and other anticoagulants)

Give an example of a commonly used drug that can injure the liver

Paracetamol