OSPAP Programme. Gastrointestinal Drugs. Dr. Adrian Moore Dale

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1 PAP Programme Dr. Adrian Moore Dale lide 1 of 26 PAP MPM14

2 Acid-Related Pathophysiology The stomach secretes: ydrochloric acid (Cl) aids digestion and also serves as a barrier to infection Bicarbonate (C 3- ) natural mechanism to prevent hyperacidity Pepsinogen an enzymatic precursor to pepsin, an enzyme that digests dietary proteins Intrinsic factor a glycoprotein that facilitates gastric absorption of vitamin B12 Mucus protects the stomach lining from both Cl and digestive enzymes Prostaglandins serve a variety of anti-inflammatory and protective functions lide 2 of 26 PAP MPM14

3 Glands of the tomach tomach is divided into three functional areas, each with specific glands Cardiac the uppermost area of the stomach by the cardiac sphincter, contains cardiac glands Pyloric pyloric zone is lowermost part of the stomach, contains the pyloric glands Gastric fundus is the larger part of the body of the stomach, contains gastric glands gastric glands play the most significant role in acid-related disorders cells of gastric gland are the largest in number and of primary importance in acid control lide 3 of 26 PAP MPM14

Cells of the Gastric Gland Parietal cells Produce and secrete Cl Primary site of action for many acid-controller drugs ydrochloric Acid ecreted by the

5 Cells of the Gastric Gland Parietal cells Produce and secrete Cl Primary site of action for many acid-controller drugs ydrochloric Acid ecreted by the parietal cells stimulated by food Large fatty meals Excessive amounts of alcohol Emotional stress Maintains stomach at p of 1 to 4 lide 15of 26 PAP MPM14

flow rate to + Cl is formed in the canaliculus Potassium ions exit the parietal cell as counterionsfor the chloride ions and

6 WEEK 34 The proton pump + /K + ATPase Pumps protons out of the parietal cell and potassium ions back in Requires energy provided by hydrolysis of ATP to ADP catalysed by ATPase Cl - departs through a separate ion channel (no energy); matched flow rate to + Cl is formed in the canaliculus Potassium ions exit the parietal cell as counterionsfor the chloride ions and are then pumped back in A separate potassium ion channel is used for K + ions leaving the cell K + canaliculus lide 6 of 26 PAP MPM14

7 Cells of the Gastric Gland (cont'd) Chief cells ecrete pepsinogen, a proenzyme Pepsinogen becomes pepsin when activated by exposure to acid Pepsin breaks down proteins (proteolytic) Mucoid cells Mucus-secreting cells (surface epithelial cells) Provide a protective mucous coat Protect against self-digestion by Cl lide 7 of 26 PAP MPM14

8 Acid-Related Diseases Imbalance of the three cells of the gastric gland and their secretions yperacidity most common overproduction of Cl by the parietal cells indigestion, sour stomach, heartburn, acid stomach PUD: peptic ulcer disease GERD: gastroesophageal reflux disease elicobacter pylori (. pylori) Bacterium found in GI tract of 90% of patients with duodenal ulcers, and 70% of those with gastric ulcers Combination therapy is used most often to eradicate. pylori lide 8 of 26 PAP MPM14

9 Acid-Controlling Agents Antacids any (non-corrosive) alkali could be used sodium (or potassium) bicarbonate calcium (or magnesium) carbonate aluminium hydroxide, magnesium trisilicate may include other agents to help alleviate condition; for example, alginates 2 antagonists cimetidine famotidine ranitidine Proton pump inhibitors lansoprazole (es)omeprazole rabeprazole pantoprazole lide 9 of 26 PAP MPM14

10 Antacids: Mechanism of Action Antacids D T prevent the over-production of acid Antacids D neutralize the acid once it s in the stomach Quick onset of relief but last for a short duration imple acid-base reaction Promote gastric mucosal defense mechanisms ecretion of: Mucus: protective barrier against Cl Bicarbonate: helps buffer acidic properties of Cl Prostaglandins: prevent activation of proton pump which results in Cl production Reduction of pain associated with acid-related disorders Raising gastric p from 1.3 to 1.6 neutralizes 50% of the gastric acid Raising gastric p 1 point (1.3 to 2.3) neutralizes 90% of the gastric acid Reducing acidity reduces pain lide 10 of 26 PAP MPM14

11 Alginates Polysaccharides derived from seaweeds Usually used as sodium salt Alginates gel in solution due to cross-linking Especially good in the presence of calcium ions Produces a raft Bicarbonate produces C 2 gas and floats raft Prevents reflux lide 11 of 26 PAP MPM14

12 2 Antagonists Reduce acid secretion All available TC in lower dosage forms Block histamine ( 2 ) at the receptors of acid-producing parietal cells production of hydrogen ions is reduced, resulting in decreased secretion from the parietal cells complete inhibition has not been shown Up to 90% inhibition of vagal and gastrin stimulated acid secretion occurs when histamine is blocked results in increase in p of the stomach lide 12 of 26 PAP MPM14

13 istamine and Gastric acid Antihistamines had no effect on Cl release KF team proposed a 2 receptor Most research groups sceptical no known 2 antagonist histamine may act by coincidentally acting at gastrin or acetylcholine receptor blocking 2 still leaves gastrin and ACh Gastrin antagonists were not easy to produce Antihistamines did not block all histamine actions dilation of blood vessels lide 13 of 26 PAP MPM14

14 Early Leads Use histamine as lead compound Many variations explored Key findings Tautomer I needs to be promoted Electron withdrawing side chain weakens basicity of α promoting tautomer I ide Chain Agonist have ionic binding Antagonists form -bonds lide 14 of 26 PAP MPM14

15 Cimetidine UK launch in 1976 biggest seller until 1988 when replaced by ranitidine Ranitidine Less side effects and 10 x more active than cimetidine All 2 antagonists may inhibit the absorption of drugs that require an acidic GI environment for absorption lide 15 of 26 PAP MPM14

Proton Pump Inhibitors (PPIs) Use of 2 antagonists allows release of acid mediated by acetylcholine or gastrin 2 antagonists largely replaced by PPI Proton pump pumps out + and it is replaced by

16 Proton Pump Inhibitors (PPIs) Use of 2 antagonists allows release of acid mediated by acetylcholine or gastrin 2 antagonists largely replaced by PPI Proton pump pumps out + and it is replaced by K + Requires energy (ATP) + produced by carbonic anhydrase (C 2 and 2 ) Irreversibly bind to + /K + ATPase enzyme Result: achlorhydria ALL gastric acid secretion is blocked lide 16 of 26 PAP MPM14

17 Proton Pump Inhibitors Almost total inhibition of gastric acid secretion Prodrugs Activated by strongly acidic conditions found in the canaliculae of parietal cells PPIs are lipophilic, weak bases omeprazole pk a 4.0; log P 2.23; bioavailability ~ 50%; BPPB ~ 95% V d ~0.4 Lkg -1, t 1/2 ~ 3h orally absorbed and delivered to parietal cells; free bases at blood p Inactive at neutral p Rapidly activated close to the target -once activated, react rapidly with the target + /K + -ATPase enzyme from systemic circulation, crosses membrane of parietal cells ionised in strongly acidic environment of secretory canaliculus of parietal cells unable to move back across the membrane resulting in accumulation in canaliculus protonation triggers an acid-catalysed conversion leading to covalent binding to a cysteine residue in the + /K + -ATPase enzyme and enzyme inhibition inhibition is irreversible and duration depends on regeneration of new pumps by parietal cells lide 17 of 26 PAP MPM14

18 pyridyl benzimidazole methylsulfinyl omeprazole 10, 20, 40 mg dispersible tablets(enterically coated pellets) 10,20,40mgcapsules 40 mg injection rabeprazol 10,20mgtablets F 3 C CF 2 lanzoprazole 15 mg capsules orodispersible tablet(enterically coated microgranules) 30 mg suspension sachet(enterically coated microgranules) pantoprazole 20,40mgtablets 40 mg injection lide 18 of 26 PAP MPM14

19 Proton Pump Inhibitors: Chirality meprazole originally marketed as a racemic mixture ulfoxides tetrahedral geometry cannot undergo pyramidal inversion (c.f. amines) omeprazole (chiral switching) -isomer : 90% gastric acid production inhibition R-isomer : 25% gastric acid production inhibition -isomer marketed as single enantiomer, esomeprazole lide 19 of 26 PAP MPM14

20 Proton Pump Inhibitors: Chirality PPIs are prodrugs Individual enantiomers are equi-potent in many pharmacodynamic test systems PPIs require an acid-mediated transformation to an achiral intermediated -omeprazole maintains intragastric p > 4 for longer reduced clearance increased systemic bioavailability interpatient variation is less other PPIs now undergoing evaluation as single enantiomer products lide 20 of 26 PAP MPM14

Proton Pump Inhibitors: Chirality Drug plasma concentrations and inhibition of pentagastrin-stimulated gastric acid secretion in healthy

21 Proton Pump Inhibitors: Chirality Drug plasma concentrations and inhibition of pentagastrin-stimulated gastric acid secretion in healthy subjects after oral administration of 15 mg of R-omeprazole, omeprazole and esomeprazole (-omeprazole) at time 0 lide 21 of 26 PAP MPM14

Proton Pump Inhibitors: Chirality Mean plasma concentration-time profiles on day 5 after daily doses of esomeprazole (40 and 20 mg) and omeprazole (20 mg) in patients with

22 Proton Pump Inhibitors: Chirality Mean plasma concentration-time profiles on day 5 after daily doses of esomeprazole (40 and 20 mg) and omeprazole (20 mg) in patients with gastroesophagealreflux disease 40 mg of esomeprazole taken orally showed much higher and more prolonged plasma concentration curves than 20 mg esomeprazole. lide 22 of 26 PAP MPM14

23 pyridinium sulfenamide sulfenic acid omeprazole 2 2 2

24 cysteineresidueof + /K + ATPAse 2 2 pyridinium sulfenic acid 2 pyridinium sulfenamide Covalent interactions with the sulphydrylgroups of cysteine residues in the extracellular domain of the + K + -ATPase in particular Cys813 thereby inhibiting its activity (omeprazole, Cys-813, Cys-892; lansoprazole, Cys-813, Cys-821, Cys-892; pantoprazole Cys-813)

25 eliobacterpylori igh rate of reappearance of stomach ulcers after PPI treatment with naturally present. pylori implicated: ighly motile;. pylori attaches to sugar molecules on the surfaces of cell lining stomach wall survives well at p close to stomach wall survives well in oxygen concentrations of ca. 5% secretes urease which hydrolyses urea, neutralising acid in local environment secrete proteins and toxins that interact with stomach epithelial cells leading to inflammation and damage potentially increases risk of gastric cancers antibiotics resistance -> eradication can be difficult (resting cocoid forms) difficulty in delivering antibiotics at therapeutic concentrations bismuth subcitrate and potassium dicitratobismuthate prevent adherence to mucosa enhance local prostaglandin synthesis, coat ulcer base, enhance adsorption of pepsin lide 25 of 26 PAP MPM14

26 eliobacterpylori Treatment 1 st line, usual to give three-part therapy for 1 week Proton pump inhibitor Two antibiotics Amoxicillin and either clarithromycin or metronidazole (clarithromycin and metronidazole) (metronidazole and tetracycline, also bismuth) lide 26 of 26 PAP MPM14

GASTROINTESTINAL AND ANTIEMETIC DRUGS. Submitted by: Shaema M. Ali

GASTROINTESTINAL AND ANTIEMETIC DRUGS Submitted by: Shaema M. Ali GASTROINTESTINAL AND ANTIEMETIC DRUGS by: Shaema M. Ali There are four common medical conditions involving the GI system 1) peptic ulcers