#5 - Gastrointestinal Flashcards
Aluminium and magnesium containing antacids
= Sodium bicarbonate not given as co2 stimulates gastrin release and so produces acid rebound effect and is absorbed by intestine so can cause systemic alkalosis.
• Magnesium hydroxide insoluble but reacts with hcl to form Mgcl + H20. Poorly absorbed from the intestines = risk of causing alkalosis is low. Magnesium trisilicate reacts slowly with gastric acid.
• Magnesium salts can produce a laxative effect and so may cause a diarrhoea.
• Aluminium hydroxide not well absorbed from intestines & neutralise HCL over a long period of hours causes constipation. So given together as they cancel each other out
• Aluminium hydroxide (C), Magnesium Carbonate (OS), Magnesium Trisilicate (T)(OS)
• Indications can include = Dyspepsia, hyperphosphatemia
Alginates are sometimes combined with antacid as it increases mucus viscosity so increasing its adherence to the intensities mucosa which makes a supporting barrier forming nature of the mucus of mucous membrane.
H2-receptor antagonists
greatly reduces gastric acid secretion but not completely as Ach and gastrin are still active
• Located on parietal cells. When stimulated by histamine released from enterochromafin cells causing the release HCL using a proton pump. Secrete H+ out K+ in. Then K+ out and Cl- out together. = HCL
• They inhibit all h2 receptor, are shorter acting and more affinity to h2 receptors in the stomach.
• Cimetidine is a cytochrome p450 inhibitor which is involved in drug metabolism.
• Cimetidine (T)(OS)(SYR), Ranitidine (T)(ET)(OS)(SYR)(INJ)
• Indications can include =Benign gastric and duodenal ulceration, chronic episodic dyspepsia, prophylaxis of NSAID-associated gastric or duodenal ulcer, GORD, gastric acid reduction, prophylaxis of stress ulceration
Proton pump inhibitors
= Irreversible inhibition of H+/K+-ATPase in gastric parietal cells
• Are inactive when administered but are activated in strong acid. They are weak bases.
• Carried around body until reach canaliculi, pass through membrane unionised liphophillic bases but once in acidic environment become protonated and cannot now come back.
• Irreversibly inhibit H+/K+-ATPase in parietal cells which causes almost no gastric acid to be produced.
• To overcome this the stomach produces new pumps, which means PPIs need to be administered daily
• Lansoprazole (T)(ODT)(SYR), Omeprazole (T)(C)(II)(INJ)
• Indications can include =Benign gastric ulcer, duodenal ulcer, NSAID-associated gastric or duodenal ulcer Eradication of H pylori associated ulcer or ulcer-like dyspepsia, Zollinger-Ellison syndrome, GORD, acid related dyspepsia
Antimotility
Agonist of the opioid µ–receptors in the gastrointestinal tract
• It is lipophilic slowly absorbed and prone to metabolism – it selectively agonises the opioid receptors in the GI tract. It cannot cross BBB and has few central actions = unlikely to cause problems of dependence
• After stimulation of the mu opioid receptors in the intestine K+ ion channels open hyperpolarizes cells and inhibits the release of neurotransmitters like acetylcholine. This reduces bowel motility.
• Loperamide (T)(C)(ODT)(OS)
• Indications can include = Acute diarrhoea and chronic diarrhoea
Aminosalicylates
Release of 5-aminosalicylic acid (5-ASA)
• Unknown mechanism of action in treating inlamamtory bowel conditions. Used for Ulceraterive Colitis
• Mesalazine (Foam/Retention Enema)(Rectal Foam)(SUP)(T)(GRAN) Sulfasalazine(T)(SUS)(ECT)(SUP)
• Indications can include = Mild to moderate and severe ulcerative colitis and maintenance of remission
Drugs effecting the immune response
= Inhibits dihydrofolate reductase
• Patients who fail to respond to anti-inflammatory steroids and 5-aminosalycylic acid can be treated with immunosuppressants such as methotrexate
• Methotrexate (T)(INJ)
• Indications can include = Inflammatory bowel disease and Crohn’s disease (unlicensed indication)
Cytokine modulators
= is a TNF inhibitor
• Used in management of severe active Chrons disease and ulcerative colitis in patients who have not had an adequate response to treatment with a corticosteroid and an immunosuppressant or if they are not intolerant of these medications.
• Risk of anaphylactic shock and delayed hypersensitivity reactions so only administered in hospital.
• Infliximab (II)
• Indications can include = Severe active Crohn’s disease and severe ulcerative colitis
Bulk-forming laxatives
Increase faecal mass, stimulating peristalsis and cause water to be retained in the stool.
• All contain polysaccharides like cellulose which is indigestible remains in lumen of intestines = bulking out intestinal contents stimulating mucousal stretch receptor to induce peristaltic movements.
• Ispaghula Husk (GRAN)(POWDER)
• Indications can include = Constipation
Stimulant laxatives
= Stimulate an increase in intestinal motility
• Stimulate/irritate the mucousa and myenteric plexus to produce intestinal movements – can cause cramps
• Senna (GRAN)(SYR)(T)
• Indications can include = Constipation
Osmotic laxatives
Holds water in the stool
• Bulk out intestinal contents with water - retain water in the bowel by osmotic effects also softening stools
• Lactulose (S)( Macrogols (Oral Powder)
• Indications can include = Constipation
Drugs used in nausea and vomiting
= Dopamine D2 antagonist
• Block dopamine D2 receptors on the CTZ & antagonize muscarinic and histamine receptors
• Metoclopramide also acts on the gi tract where it increases motility to treat gastro-oesophageal reflux
• Prochlorperazine (T)(SYR)(INJ)(BUCCAL TAB) Domperidone (T)(OS) Metoclopramide (T)(OS)(INJ)
• Indications can include = Severe nausea, vomiting, vertigo, labyrinthine disorders
5HT3-receptor antagonists
- Acts directly on the 5-HT3 receptors of the CTZ as well as 5-HT3 receptors that occur in places like the intestine. Although 5-HT3 is widely used throughout the body, the GI tract holds 90% of the body’s total.
- Ondansetron (T)(OS)(ODT)(FILM)(INJ)(SUP)(ORAL LYPHILISATES)
- Indications can include = Moderate and severe emetogenic chemotherapy or radiotherapy
Antihistamines
Histamine H1 receptor antagonist
• Antagonizes H1 receptors on the vomiting centre, however they are not very effective against CTZ stimuli
• Cyclizine (T)(INJ)
• Indications can include = Nausea, vomiting, vertigo, motion sickness, labyrinthine disorders
