Drugs Affecting the Gastrointestinal Tract and Antiemetic Drugs Flashcards
Amoxicillin (AMOXIL, TRIMOX); “Bismuth compounds (PEPTO-BISMOL, KAOPECTATE)”; Clarithromycin (BIAXIN); Metronidazole (FLAGYL); Tetracycline (Sumycin)
Pharmacodynamics: Antimicrobial agent;
Indications for use: Used to treat gastric ulcers (duodenal as well) caused by H.pylori leading to rapid healing and low recurrence.
Clinical information: given as triple therapy (PPIs + Amoxicillin (Metronidazole if allergic) + Clarithromycin) alternatively there is quadruple therapy (pepto-bismol + metranidazole + tetracycline + PPI).
N.B Bismuth compounds can be used as an agent to modify fluid and electrolyte transport.
Cimetidine (TAGAMET); “Famotidine (PEPCID)”; Nizatidine (AXID); Ranitidine (ZANTAC)
Pharmacodynamics: H2 - histamine receptor blockers (reversible competitive antagonist);
Indications for use: used to treat peptic ulcers (if-NSAID induced then PPIs should be used), acute stress ulcers (temporary), gastroesophageal reflux disease;
Clinical information: also inhibits basal, food stimulated and nocturnal stimulation; the use of these has been diminished due to PPIs.
Dexlansoprazole (DEXILANT); Esomeprazole (NEXIUM); Lansoprazole (PREVACID); “Omeprazole (PRILOSEC)”; Pantoprazole (PROTONIX); Rabeprazole (ACIPHEX)
Pharmacodynamics: Proton pump inhibitors (PPIs) bind directly H+/K+ ATPase (lasts for 18 hours);
Indications for use: Used in treatment of GERD, prophylaxis in conjunction with NSAIDS to prevent ulcerations of the stomach, erosive esophagitis, active ulcers and diseases such as Zollinger - Ellison (gastrin producing tumor) and used in treatment of H.pylori ulcers.
“Misoprostol (CYTOTEC)”
Pharmacodynamics: Prostoglandin E inhibits gastric secretion and promotes secretion of mucus and bicarbonate;
Indications for use: Used to treat peptic ulcers caused by deficiency in prostoglandin E, should be given as prophylaxis for people who take NSAIDs;
Contraindication: pregnancy (can cause premature uterine contractions).
Dicyclomine (BENTYL)
Pharmacodynamics: Antimuscarinic agents;
Indications for use:
“Aluminium hydroxide (ALTERNAGEL)”; “Calcium carbonate (TUMS)”; “Magnesium hydroxide (MILK OF MAGNESIA)”; Sodium bicarbonate
Pharmacodynamics: Antacids weak bases that react with gastric acid to form water and reduce pepsin activity by inactivating it in alkaline conditions;
Indications for use: used to control symptoms of peptic ulcers and treat GERD;
Contraindication: in renal patients due to absorption of cations;
Side effects: Aluminium causes constipation and magnesium causes diarrhoea.
“Bismuth subsalicylate (PEPTO-BISMOL)”; Sucralfate (CARAFATE)
Pharmacodynamics: Mucosal protective agents;
Indications for use: Sucralfate used in treatment of peptic ulcer as aluminium and sucrose bind to proteins on necrotic tissue and form a protective gel;
Bismuth part of quadruple therapy to treat peptic ulcers inhibits pepsin, increases mucus secretion, interacts with glycoproteins forming a protective coating on the mucosa;
Contraindication: Sucrasulfate requires acid to should not be given with PPIs, H2 antagonists and antacids.
Prochlorperazine (COMPAZINE)
Pharmacodynamics: Phenothiazines block dopamine receptors;
Indications for use: used to control chemotherapy-induced nausea and vomiting.
Granisetron (KYTRIL); Palonosetron (ALOXI); “Ondansetron (ZOFRAN)”; Dolasetron (ANZEMET) (last two no longer used due to prolonging of QTc interval)
Pharmacodynamics: 5-HT3 serotonin receptor blockers (antagonists) in the periphery and the CTZ long duration and high efficacy;
Indications for use: used to control chemotherapy-induced and post operative nausea and vomiting;
Contraindications: ondansetron requires a dose adjustment in hepatically impaired patients.
“Metocloperamide (REGLAN)”
Pharmacodynammics: Substituted benzamides leading to inhibition of dopamine in the CTZ ;
Indications for use: used to control chemotherapy-induced (cisplatin) nausea and vomiting;
Side effects: Can cause extrapyrimidal effects so should not be used long term or for GERD.
Droperidol; Haloperidol (HALDOL)
Pharmacodynamics: Butyrophenones block dopamine receptors;
Indications for use: used to control chemotherapy-induced (cisplatin) nausea and vomiting;
Side - effects: prolongs QTc interval.
Alprazolam (XANAX); Lorazepam (ATIVAN)
Pharmacodynamics: Benzodiazepines GABA-A agonists mostly due to sedative, anxiolytic and amnesic properties (prophylaxis);
Indications for use: used to control chemotherapy-induced nausea and vomiting;
Contraindications: alcohol (CNS depression).
Dexamethasone (DECADRON); Methylprednisolone (MEDRIOL)
Pharmacodynamics: corticosteroids (blockade of prostoglandins?);
Indications for use: used to control chemotherapy-induced nausea and vomiting.
Aprepitant (EMEND)
Pharmacodynamics: Substance p/neurokinin-1 receptor blocker targets neurokinin receptor and blocks action of substance P;
Indications for use: used to control chemotherapy-induced nausea and vomiting;
Clinical information: Given along side dexamethasone and 5-HT3 antagonists;
Contraindications: metabolised by CYP3A4 so effects metabolism of warfarin and oral contraceptives.
How do H2 receptor antagonists regulate gastric acid secretion?
Secretion is stimulated by histamine as well as gastrin and ACh. Receptor binding –> activates protein kinase –> stimulates H+/K+ ATPase PP –> exchange of H+ and K+ into the stomach. Blocking of H2 reduces secretion.
What are the side effects of H2 receptor antagonists?
Mostly well tolerated. Cimetidine has endocrine effects (nonsteroidal anti-androgen) leading to gynocomastia and galactorrhea (release of prolactin), CNS effects (confusion and altered mental state in the elderly), inhibits CYP450 and the metabolism of warfarin, phenytoin and clopidogrel. All reduce the effect of drugs such as ketoconzole that require acid for absorption.
Diphenoxylate + atropine (LOMOTIL); “Loperamide (IMODIUM A-D)”
Pharmacodynamics: anti-motility agents have opioid like action on gut blocking pre-synaptic opioid receptors in the enteric NS decreasing peristalsis by reducing release of ACh;
Indications for use: Used in treatment of diarrhoea;
Side - effect: can cause toxic megacolon.
“Aluminium hydroxide” (ALTERNAGEL); Methylcellulose (CITRUCEL)
Pharmacodynamics: adsorb intestinal toxins and microorganisms and protecting the intestinal mucosa - methyl cellulose is also a bulk laxative;
Indications for use: treatment of diarrhoea;
Contraindication: interfere with the absorption of other drugs.
“Bisacodyl (CORRECTOL, DULCOLAX)”; Castor oil; “Senna (SENOKOT)”
Pharmacodynamics: irritants and stimulants - anthraquinone glycosides causing electrolyte and water secretion into bowels, bisacodyl acts on nerve fibres in the mucosa of the colon and castor oil’s product (ricinoleic acid) irritates the stomach producing peristalsis;
Indications for use: Used as laxatives;
Contraindications: can cause uterine contractions so should not be used in pregnancy.
Psyllium (METAMUCIL, FIBERALL)
Pharmacodynamics: Bulk laxative - hydrophilic colloids form gels in large intestine causing fluid retention and distention increasing peristalsis;
Indications for use: Used as a laxative;
Contraindications: Potentially can cause an obstruction so should not be given to those who are immobile.
“Magnesium citrate (CITROMA); Magnsium hydroxide (MILK OF MAGNESIA)”; Polyethylene glycol / “Sodium picosulfate” (used for gastric lavage before surgery) (MIRALAX, GOLYTELY, MOVIPREP, NULYTELY, TRILYTE); Lactulose
Pharmacodynamics: Saline and osmotic laxative - hold water via osmosis (increased salt or sugar concentration within the lumen) causing peristalsis;
Indications for use: Laxative (PEG specifically used for colonic lavage and causes less cramping and gas), lactulose used to treat hepatic encephalopathy as it reduces ammonia levels.
Docusate (COLACE, DOCU-SOFT)
Pharmacodynamics: stool softener - surface active agents –> emulsified with stool to produce softer feces;
Indications for use: prophylactic laxative;
Contraindications: should not be taken with mineral oil as it will be absorbed.
Glycerin suppositories, Mineral oil
Pharmacodynamics: lubricant;
Indications for use: laxative;
Clinical information: mineral oil should be taken upright to avoid aspiration and lipoid pneumonia.
Lubiprostone (AMITIZA)
Pharmacodynamics: Chloride channel activators increasing fluid secretion into the intestinal lumen;
Indications for use: laxative for chronic constipation as no tolerance, dependency, electrolyte imbalance or chronic constipation;
No contraindications as metabolism occurs in stomach and jejunum.
