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Questions and Answers
Which of the following are types of acid-reducing agents? (Select all that apply)
What is the prototype drug for H2 antihistamines?
Cimetidine
Which of the following drugs are examples of Proton Pump Inhibitors?
What is the mechanism of action of Proton Pump Inhibitors?
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Cimetidine has a higher incidence of adverse effects compared to newer H2 blockers.
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What percentage of acid output can Cimetidine reduce over 24 hours?
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Which of the following is a side effect of Cimetidine?
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What is the role of Sucralfate in acid-related treatment?
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Match the drug with its primary action:
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What is the bioavailability percentage of Cimetidine?
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Study Notes
Gastric Acid Reduction
- H2 blockers: Cimetidine, Ranitidine, Famotidine, Roxatidine
- Suppress all phases of gastric acid secretion, including basal, psychic, and neurogenic
- Cimetidine is the prototype, it suppresses nocturnal basal gastric acid secretion more completely
- H2 blockers can prevent ulceration due to stress or drugs
Proton Pump Inhibitors
- Omeprazole, Lansoprazole, Pantoprazole, Rabeprazole, Esomeprazole are all PPIs.
- Inhibit the final common step in gastric acid secretion
- More effective than H2 blockers for acid-peptic disorders
- Can totally abolish HCl secretion, both resting and stimulated
- Omeprazole is the prototype, it is active at pH < 5
- PPIs irreversibly inactivate H+K+ATPase enzyme
- Acid secretion resumes only when new H+K+ATPase molecules are synthesized
- PPIs also inhibit gastric mucosal carbonic anhydrase
Antacids
- Neutralize gastric acid
- Systemic: Sodium Bicarbonate, Sod.Citrate
- Non Systemic: Magnesium Hydroxide, Mag.Trisilicate, Aluminium Hydroxide Gel, Magaldrate, Calcium Carbonate
Other Drugs For Acid Suppression
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Anticholinergics: Pirezepine, Propantheline, Oxyphenonium
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Prostaglandin Analogue: Misoprostol
Ulcer Protectives
- Sucralfate, Colloidal Bismuth subcitrate (CBS)
Anti-H.Pylori Drugs
- Amoxycillin, Clarithromycin, Metronidazole, Tinidazole, Tetracycline
Cimetidine
- 60-70% reduction of 24hr acid output
- 60-80% bioavailability. First pass hepatic metabolism
- Excreted in urine & bile
- T1/2: 2-3hrs
Adverse Effects of Cimetidine
- Headache, dizziness, bowel upset, dry mouth, rashes
- Confusion, restlessness, convulsions, coma
- Bolus IV administration can release histamine resulting in bradycardia, arrhythmia, cardiac arrest
- Cimetidine displaces dihydrotestosterone from its cytoplasmic receptor, increases prolactin levels, and decreases estradiol degradation by the liver
- Transient rise in aminotransferases
Cimetidine Drug Interactions
- Inhibits CYP 450 enzymes
- Interact with warfarin, phenobarbitone, theophylline and phenytoin
- Antacids reduce absorption of H2 blockers
- H2 Blockers reduce absorption of ketoconazole
Ranitidine
- 5x more potent than Cimetidine
- Longer duration of action (> 24hrs of suppression)
- Little effect outside the GIT, less permeability into the brain
- Does not inhibit hepatic metabolism
- Lower incidence of adverse effects overall
Famotidine
- Longer duration of action
- T1/2: 2.5-3.5 hrs
- 5-8 x more potent than Ranitidine
- Low affinity for CYP-450
- 40-50% bioavailability
- 70% excreted unchanged
Roxatidine
- Twice as potent and longer acting than Ranitidine
H2 Blockers in Duodenal Ulcers
- Rapid and marked pain relief in 2-3 days
- 60-85% heal at 4 weeks; 70-95% at 8 weeks
- About ½ the patients relapse, maintenance therapy reduces the relapse rate by 15-20%/year
H2 Blockers in Gastric Ulcers
- Healing rates somewhat lower 50-75% at 8 weeks)
- Can heal NSAID associated ulcers
- Less effective than PPIs & Misoprostol
H2 Blockers in Acute Stressful Conditions
- Hepatic coma, severe burns, trauma, prolonged intensive care, asphyxia neonatorum, etc.
- IV H2 blockers prevent gastric lesions and hemorrhage
H2 Blockers in Zollinger-Ellison Syndrome
- Gastrin secreting tumor
- H2 blockers in high doses control hyperacidity, but relief is incomplete
- PPIs are the drug of choice
- Definitive treatment is surgical
H2 Blockers in GERD
- Afford symptomatic relief and facilitate healing of oesophageal erosions
- 2-3 divided doses
H2 Blockers in Prophylaxis of Aspiration Pneumonia
- Preoperatively
Omeprazole
- Prototype PPI
- Best taken empty stomach
- Highly plasma protein bound
- Rapidly metabolized in the liver
- No dose adjustment required in elderly or renal/hepatic impairment
- Secretion resumes gradually over 3-5 days after discontinuation
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Description
This quiz covers the mechanisms and classifications of various acid-reducing agents, including H2 blockers, proton pump inhibitors (PPIs), and antacids. It highlights the prototypes of each class and their effects on gastric acid secretion. Test your knowledge on these medications and their therapeutic uses in managing acid-peptic disorders.
