Proton Pump Inhibitors and Acid Suppression Drugs
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Direct answer
Proton pump inhibitors are prodrugs that irreversibly block the H+/K+ ATPase of the gastric parietal cell, giving the most potent acid suppression of any common drug class. H2 receptor antagonists block histamine receptors and are less potent, while sucralfate forms a protective barrier over ulcers and misoprostol is a prostaglandin E1 analogue. Omeprazole, pantoprazole and rabeprazole are the commonly used PPIs, and all are activated only in the acidic canaliculus.
What you must remember
- PPI mechanism: the drug binds cysteine residues of the proton pump after activation, so acid secretion resumes only when new pumps are synthesised.
- Timing: PPIs are taken 30 to 60 minutes before a meal, because the pumps must be active for the drug to be activated.
- H2 blockers: famotidine and cimetidine are examples; cimetidine inhibits cytochrome P450 enzymes, and ranitidine has been withdrawn in many markets.
- Sucralfate: an aluminium salt that binds to the ulcer crater and must be separated from other drugs by about two hours.
- Misoprostol: a prostaglandin E1 analogue used to prevent NSAID ulcers, with diarrhoea as the main limit and pregnancy as an absolute contraindication.
- Long-term PPI adverse effects: Clostridioides difficile infection, hypomagnesaemia, fracture, vitamin B12 deficiency and interstitial nephritis.
- Absorption interactions: PPIs reduce absorption of iron, vitamin B12 and azole antifungals such as ketoconazole, which need an acidic stomach.
- Clopidogrel: omeprazole and esomeprazole reduce its activation through CYP2C19, so pantoprazole is preferred.
Choosing an acid suppression drug, by mechanism and use
The drugs differ in where they act along the acid pathway, and that difference decides both the indication and the adverse effects. The table compares the four classes most often tested, and each row names the one point a student is most likely to be asked about in the exam.
| Drug class | Mechanism | Typical use | Key point |
|---|---|---|---|
| PPI | Irreversible H+/K+ ATPase block | Peptic ulcer, GERD, NSAID gastroprotection | Most potent; take before meals |
| H2 blocker | Blocks histamine H2 receptors | Mild acid disorders, nocturnal acid | Less potent; renal dose adjustment |
| Sucralfate | Protective barrier over ulcer | Duodenal ulcer | Binds other drugs; separate doses |
| Misoprostol | PGE1 analogue, mucosal protection | NSAID ulcer prevention | Contraindicated in pregnancy |
The PPI is the most potent and most often prescribed class, while sucralfate and misoprostol protect the mucosa rather than suppress acid. Choosing a class is therefore a question of mechanism and indication, not simply of which drug is strongest.
Where the exam tries to catch you
The stem often describes timing, a combination or a pregnant patient, and the trap is a plausible but wrong drug.
- Trap: taking a PPI after meals for maximum effect Correct: a PPI is taken before meals, because the pumps must be active for the drug to work.
- Trap: treating sucralfate as an acid-suppressing drug Correct: it is a mucosal protectant that binds the ulcer crater, so it does not raise gastric pH.
- Trap: prescribing misoprostol in pregnancy Correct: it is contraindicated because it causes uterine contractions and abortion.
- Trap: considering omeprazole safe with clopidogrel Correct: pantoprazole is preferred because omeprazole reduces clopidogrel activation.
Frequently asked questions
Why are proton pump inhibitors taken before meals?
Proton pump inhibitors are taken before meals because they act only on active proton pumps, which are switched on by food. Taking the drug 30 to 60 minutes before eating gives the best acid suppression during the meal.
What is the main drug interaction of sucralfate?
Sucralfate binds other drugs in the gut and reduces their absorption, so it must be taken apart from them. Separating sucralfate from other drugs by about two hours is the usual advice, and fluoroquinolones and levothyroxine are classic examples affected.
What adverse effects follow long-term proton pump inhibitor therapy?
Long-term proton pump inhibitor therapy is associated with Clostridioides difficile infection, hypomagnesaemia, fractures, vitamin B12 deficiency and interstitial nephritis. The risk rises with duration, so the lowest effective dose and a periodic review are advised.
When is misoprostol used in gastroenterology?
Misoprostol is used to prevent NSAID-induced gastric ulcers, especially in patients at high risk who cannot take a proton pump inhibitor. Its use is limited by diarrhoea and it must never be given in pregnancy.