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Regulation of acid secretion (Antacids (Preparations (drugs): …
Regulation of acid secretion
Proton Pump Inhibitors
Drugs:
Omeprazole, esomeprazole, lansoprazole, pantoprazole, rabeprazole
Mechanism of action:
Irreversibly inhibits the H+/K+ ATPase (the proton pump) on parietal cells
Clinical effects:
Inhibits the final step of acid secretion which stimulates both basal & food stimulated acid secretion
This reduces acid secretion by 99%
Adverse effects:
Well tolerated
Drug interactions:
Some inhibition of cytochrome P450 enzymes
H2 receptor antagonists
Drugs:
Cimetidine, famotidine, nizatidine, ranitidine
Mechanism of action:
Competitively inhibits histamine & gastrin stimulated acid secretion by antagonising H2 receptors on parietal cells
Clinical effects:
Decreases both basal & food stimulated acid secretion by 90% or more
Adverse effects:
Well tolerated
Cimetidine has a modest affinity for androgen receptors and can cause gynaecomastia & sexual dysfunction in males
Drug interactions:
Cimetidine inhibits many cytochrome P450 enzymes resulting in many drug interactions
Antacids
Preparations (drugs):
Aluminium/calcium/magnesium/sodium salts of hydroxide/carbonate
Mechanism of action:
Basic salts neutralise gastric acid (acid + base --> salt + water)
Clinical effects:
Neutralisation of gastric acid
Adverse effects:
Constipation (Aluminium/calcium products)
Diarrhoea (Magnesium products)
Precautions:
Aluminium/magnesium products can cause hypermagnasaemia and aluminium toxicity in patients with renal failure
Sodium products should be avoided in those with hypertension, cardiac failure, renal impairment, ascites & peripheral oedema
Drug interactions:
May impair the absorption of other orally administered drugs
Cytoprotective agents
Sucralfate
Mechanism of action:
A complex of aluminium hydroxide & sulphated sucrose which releases aluminium in the presence of acid
The residual complex can form complex gels with mucous which decreases the degradation of mucous by pepsin and limits the diffusion of H+
Adverse effects:
Constipation (<15% chance)
Risk of aluminium toxicity with renal impairment
Drug interactions:
May impair the absorption of orally administered drugs
Bismuth subcitrate
Mechanism of action:
Increases mucous glycoprotein secretion and may also bind to gastric mucous layer to act as a diffusion barrier to H+
Has a cytoprotective effect and increases mucosal secretion of prostaglandins & bicarbonate
Also is bactericidal effects against Helicobacter pylori and prevents adhesion of H. pylori to epithelial cells
Adverse effects:
May cause nausea, vomiting and blackening of the tongue and faeces
May reach toxic levels with renal impairment which can cause encephalopathy
Availability:
Not available in Australia but may be available through the Special Access Scheme
Misoprostol
Mechanism of action:
Mimics prostaglandin E1 which activates different EP receptors on different cells
Clinical effects:
Protects GI mucosa by increasing the secretion of mucous & bicarbonate and decreases basal & food stimulated acid secretion
Adverse effects:
Poorly tolerated
Commonly causes nausea, vomiting, diarrhoea, uterine cramps (an abortion drug)