GI Drugs Flashcards by Nasiruddin Patel

GORD/GERD

Treatments = Antacids, Histamine H2 antagonists, PPI

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Antacids:

Drugs = Aluminium Salts, Magnesium Salts

Mechanism:
= Neutralise acid, inactivate pepsin/peptic enzymes
= Can heal ulcers

Aluminium Salts: maintain chloride reabsorption from intestine
- - - Constipation

Magnesium Salts: absorbs pepsin/inhibits pepsin
- - - Diarrhoea

!!! Calcium Salts/milk not used as they stimulate gastrin release = enhanced acid secretion

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Histamine H2 Antagonists

Drugs = Famotidine, Nizatidine, Cimetidine

Mechanism
= inhibitor of H2 receptor in parietal cells
= DEC. histamine induced cAMP
= DEC. stimulation of proton pump

+ DEC. Basal/food stimulated
+ DEC. pepsin
+ DEC. gastric juice

- - Diarrhoea
- - Headache
- - Dizziness

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PPI

Drugs = Omeprazole, Lansoprazole

Mechanism
= Inhibits H+/K+ ATPase by irreversible secretion
= Inhibits acid secretion
= Metabolised at acidic pH, thus given in enteric adminstered granules

+ H/K+ Atpase inhibition

Liver interaction = DEC dose in liver disease
Diarrhoea - Headaches

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IBD

Drugs = 5-ASA Aminosalicylates, Glucocorticoids, Antiproliferative Immunosuppressants, Calcineurin Inhibitors, TNF-a Inhibitors

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Aminosalicylates 5-ASA

Drugs = Balasalzide, Mesalazine (in UC!)

Mechanism
= Free-radical scavenger that decreases inflammation
= Acts on PPAR-Y nuclear receptor
= DEC. in Leukotriene’s B4 & IL-1

+ Maintains emission
+ Prevents leukocyte recruitment into bowel by inhibiting chemotaxis & cellular adhesion

- - Blood dyscrasias e.g. bleeding, bruising
- - Sore throat, diarrhoea, nephritis
- - Agranulocytosis (DEC. in WBC)
- - Hypospermia

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Glucocorticoids

Drugs = Budesonide, Prednisolone, Beclomethasone (CD!)

Mechanism
= Anti-inflammatory & immunosuppressive
= INC. in Lipocortin = DEC. in AA
= DEC. T-cell activation/proliferation
= Acute exacerbations via rectal foam

+ Gastro-resistant, enteric delivery
+ High 1st pass metabolism (= low conc.)

INC. in Cortisol = Cushing’s

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Antiproliferative Immunosuppressants

Drugs = Cyclophosphamide, Methotrexate, Azathioprine

Mechanism
= Generates fraudulent nucleotide 6-thio-GTP
= Long term maintenance, not for acute exacerbations

+ Steroid sparing = less long term risks

BM depression (inhibits RNA/DNA synthesis via IL2 block)
Pancreatitis

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Calcineurin Inhibitors (Immunomodulators)

Drugs = Ciclosporin, Tacrolimus

Mechanism
= IL-2 transcription = DEC. in lymphocyte proliferation

CD = effective for exacerbations
= reduced fistulas

UC = only if steroid therapy hasn’t worked

+ No BM suppression

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TNF-a Inhibitors

Drugs = Infliximab, Adalimumab (used in CD!)

Infliximab
= Neutralises TNF-a in ECF via chemical neutralisation
+ Acute flares, fistulas closure, remission
- TB, hepatitis, HF C/l, NHL

Adalimumab
= No dose? INC to weekly dose
!!! Discontinue if no response after 12 weeks

!!!!! Etanercept used as they cannot bind to & neutralise TNF-a

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IBS

Drugs = Antispasmodics, Peppermint Oil, Lubiprostone, Linaclotide

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Antispasmodics

Hyoscine Butylbromide/Buscopan (Muscarinic Cholinergic Antagonists)

= Induced by Ach & via M3 receptors where cholinergic reaction is blocked
+ DEC. absorption of ammonium compounds
- Dry mouth, blurred vision, urinary retention

Mebevarine (colofac)
= Direct action on smooth muscle of stomach, rather than stomach lining

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Lubiprostone

IBS-C

+ Generation of chloride rich fluid

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Diarrhoea

Loperamide

= U-opiod agonist
= DEC. myenteric plexus activity
= DEC. GI motility enhancing ion/water
- Constipation

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Constipation

Laxatives = INC. GI motility

• Bulk = Ispaghula Husk (Fybrogel)
= Absorbs weight in water

• Osmotic = Lactulose
= Treats high ammonium levels in HE
- - - Unsuitable for IBS due to bloating

• Stimulant = Senna
= Stimulates peristalsis by acting on
myenteric plexus

Dopamine Antagonists 
(Domperidone, Metoclopramide)

+ LOS + Gastric emptying
+ Enhance duodenal peristalsis

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Anti-Emetic Drugs

Cholinergic Muscarinic Antagonists

Drug = Hyoscine Hydrobromide (ear patch)

+ Travel sickness + Less drowsy (unlike H2A)
- - - Dry mouth, blurred vision

Histamine H1 Antagonists

Drugs = Cinnazirine, Cyclizine, Promethazine

+ Motion sickness
+ Stomach irritants, pregnancy sickness

Drowsiness, sedation

Dopamine (D2) Antagonists

• Metoclopramide

+ CTZ action
+ INC. in peripheral motility

- - Blockade of dopamine receptors = fatigue, INC. prolactin

• Domperidone
+ Doesn’t cross BBB = DEC. CNS effects
+ CTZ more accessible

Which antibody is effective in neutralising the cytokine, TNFalpha, in the treatment of Crohn’s disease?

Infliximab

Which antibiotic combination would be effective in treating H.pylori postive duodenal ulcers?

clarithromycin + amoxicillin

Which agent could you use to treat constipation in a patient resistant to the effect of senna?

Prucalopride

A 48 year old man with a history of polymyalgia rheumatic attends A & E complaining of abdominal pain and having noticed some blood in his stools. Amongst your differential diagnoses is peptic ulcer.

Select one of the following prescribed drugs most likely to contribute to his peptic ulcer disease?

Naproxen (COX inhibitor, which reduces prostaglandin synthesis, reducing protective mucosal barrier)

What is the most important difference between the antiemetics metoclopramide and domperidone?

Domperidone doesn’t cross the blood brain barrier

Which drug would be most useful in treating irritable bowel syndrome associated with constipation (IBS-C)?

Lubiprostone &/or Mebeverine (Colofac)

Which of the following drugs is commonly used to prevent travel sickness?

Hyoscine ear patch (Cholinergic Muscarinic Antagonist)

Why isn’t Loperamide used as an analgesic in palliative care?

Doesn't cross BBB (u-opiod agonist)

A 72 yeat old woman is admitted by her GP as she has not opened her bowels for 5 days. She denies any pain and feels well in herself. Her past medical history include hypertension, hypercholesterolemia and osteoarthritis. Which prescribed drug is most likely to be the cause of her constipation?

Co-codamol (u-opiod agonist = inhibiting myenteric plexus = reducing peristalsis = constipation

What is the major difference between proton pump inhibitors, Omeprazole and Rabeprazole?

Rabeprazole is NOT metabolised by the liver

Which drug mechanism would be most effective in treating diarrhoea?

U-opiod agonist

Which drug is most effective in anticipatory vomiting due to cancer chemotherapy?

Lorazepam (benzodiazepine)

Activation of which epithelial ion channel is used to treat IBS with constipation (IBS-C)?

Chloride

Which drug, together with antibiotics, is used to treat duodenal ulcer due to H. pylori?

PPI

Which preparation of a steroid might be most effective in treating ulcerative colitis?

Rectal foam

One of your patients, a 68 year old lady making a good recovery from hip surgery, requests a laxative as she has not opened her bowels for 4 days. She is now mobilising, but you attribute her constipation to recent immobility. She reports feeling slightly bloated but denies having cramps. An abdominal x-ray reveals no evidence of obstruction and digital rectal examination reveals fairly soft stools. She says she would prefer something by the oral route in the first instance. Which drug would be the most appropriate to relieve her constipation?

Senna