What Lansoprazole Is
Lansoprazole is a proton pump inhibitor belonging to the benzimidazole class. It is used to treat acid-related disorders of the upper gastrointestinal tract, including gastric and duodenal ulcers, reflux esophagitis, ulceration associated with anti-inflammatory drugs and Zollinger-Ellison syndrome. The molecule is a prodrug with little activity of its own: it must be converted inside the acid-secreting cell before it can block acid production. That activation step explains why the drug is formulated as an enteric-coated delayed-release product and why its effect lasts far longer than its plasma half-life.
Step 1: How the Gastric Proton Pump Secretes Acid
Parietal cells in the gastric mucosa contain a membrane enzyme called the proton pump, or H+/K+-ATPase, which sits in the secretory canaliculus. The pump moves hydrogen ions from the cytoplasm into the gastric lumen and potassium ions in the opposite direction. This exchange is an active transport process that consumes ATP. Because hydrogen ion secretion is the final step in acid production, the gastric juice that results is essentially hydrochloric acid. Blocking the pump therefore blocks acid secretion at its source instead of merely buffering acid that is already present.
Step 2: Acid Activation of Lansoprazole
Lansoprazole is a weakly basic, fat-soluble compound, so it concentrates in the acidic environment of the secretory canaliculus. There the low pH triggers a rearrangement that converts the prodrug into a reactive sulfenamide intermediate. This intermediate binds to sulfhydryl groups on cysteine residues of the proton pump and forms a covalent disulfide bond that is effectively irreversible. The pump can no longer transport hydrogen ions, and the drug remains trapped at the canalicular membrane, which is why it accumulates exactly where it is needed.
Step 3: Why the Acid Suppression Lasts So Long
Because the inhibition is covalent and irreversible, acid secretion recovers only when the parietal cell synthesises new proton pump molecules. A single dose therefore produces prolonged suppression of both basal and stimulated acid secretion, and repeated daily dosing builds a steady-state effect. This is the pharmacological reason proton pump inhibitors are dosed once daily rather than repeatedly through the day.
Step 4: Clinical Consequences of Proton Pump Blockade
Gastric and duodenal ulcers: a lower acid load and reduced pepsin activity let the ulcer base heal and relieve pain.
Reflux esophagitis: less acidic and smaller volume refluxate reduces irritation of the esophageal mucosa, easing heartburn and retrosternal pain and supporting mucosal repair.
Zollinger-Ellison syndrome: the very high acid output driven by gastrin excess is controlled, reducing severe ulceration and diarrhoea.
Bacterial eradication therapy: acid suppression raises intragastric pH, which improves the stability and activity of co-administered antibiotics in standard regimens.
Anti-inflammatory drug injury: lowering intragastric acidity reduces the risk of mucosal damage in patients who must continue long-term treatment.
Formulation, Dosing and Metabolism
| Property | Detail |
|---|---|
| Drug class | Proton pump inhibitor, benzimidazole derivative |
| Molecular target | H+/K+-ATPase in gastric parietal cells |
| Type of inhibition | Covalent and irreversible |
| Typical adult dose | 15 to 30 mg once daily, higher in gastrinoma |
| Dosage form | Enteric-coated delayed-release capsules or tablets |
| Main metabolic route | Hepatic, via CYP2C19 and CYP3A4 |
Because lansoprazole is destroyed by gastric acid before it can be absorbed, the granules are enteric coated so that release occurs in the small intestine. Administration before the first meal of the day is preferred, since the number of actively secreting pumps is highest after a prolonged fast. Metabolism is mainly hepatic through CYP2C19, and genetic variation in this enzyme contributes to differences in exposure between patients, while co-administration of drugs handled by the same pathway can alter plasma levels.
FAQ
Q: Is lansoprazole an irreversible inhibitor?
Yes. The activated drug forms a covalent disulfide bond with the proton pump, so activity returns only after new pump molecules are synthesised.
Q: Why is lansoprazole supplied as an enteric-coated capsule?
The drug is acid labile. The enteric coat prevents release in the stomach so that the dose reaches the small intestine intact and can be absorbed.
Q: How is lansoprazole activated in the body?
It accumulates in the acidic secretory canaliculus of parietal cells, where acid converts it into a reactive sulfenamide that binds the pump.
Q: Which conditions are treated with lansoprazole?
Gastric and duodenal ulcers, reflux esophagitis, ulcers linked to anti-inflammatory drugs, bacterial eradication regimens and Zollinger-Ellison syndrome.
Q: Why does acid secretion recover slowly after treatment stops?
Because inhibition is covalent rather than competitive, secretion returns only as parietal cells replace the blocked pump protein.
Q: When should the dose be taken?
Before the first meal of the day, when a large population of newly activated proton pumps is available to be blocked.
