Proton Pump Inhibitors bind to an enzyme system H+/K+ – ATPase. This system is the proton pump in the stomach’s parietal cells, and the drugs inhibiting it suppresses the secretion of hydrogen ions into the gastric lumen.
Drugs – esomeprazole, lansoprazole, omeprazole, pantoprazole, rabeprazole
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What are Antiulcer Drugs?
As the name suggests, the agents under this drug class are used to manage and treat ulcers in the stomach, both peptic and duodenal. Ulcers in the stomach occur when any part of GIT gets directly exposed to gastric acid and pepsin. The etiology of peptic ulcers is unclear, and several factors are responsible for triggering them.
Generally, it results from an imbalance between aggressive (pepsin, bile, Helicobacter pylori, acid) and defensive (gastric mucus, bicarbonates, prostaglandins nitric oxide, high mucosal blood flow, innate resistance of the mucosal cells) mechanisms. Thus, the drugs used for ulcers prevent aggressive factors and aid the defensive factors for an overall healing effect.
Proton Pump Inhibitors: Pharmacokinetic Properties
| PPIs | Volume of Distribution (Vd) | Half-life (t1/2) | Bioavailability | Protein Binding | Route of elimination | Metabolites |
| omeprazole | 0.3L/kg | 0.5 – 1 hr | 30 – 40% | 95% | 80% of a given dose is excreted in the urine, and the remainder via the bile. | Plasma metabolites:5-Hydroxy omeprazole,Omeprazole sulfide,Omeprazole sulfone,3-Hydroxy omeprazole.Urinary metabolites:Hydroxyomeprazole, Corresponding carboxylic acid. |
| Esomeprazole | 16L | 1 – 1.5 hrs | 90% | 97% | 80% of the oral dose of esomeprazole is excreted in the urine, and the remainder in the bile. | Plasma metabolites:5-O-desmethyl- and sulphone derivatives and Hydroxy esomeprazole.Urinary metabolites:Hydroxy omeprazole, Corresponding carboxylic acid. |
| Lansoprazole | 0.4 L/kg | 2 hrs or less | 80 – 90% | 97% | 14-23% eliminated in the urine (conjugated and unconjugated hydroxylated metabolites). | 5-Hydroxy lansoprazole,Lansoprazole sulfone. |
| Pantoprazole | 11.0-23.6 L | ~ 1 hr | 77% | ~ 98% | 71% of the dose was excreted in the urine as inactive metabolites, with 18% excreted in the bile. | Desmethylpantoprazole (main metabolite),Pantoprazole sulfate,Pantoprazole sulfone. |
| Rabeprazole | 0.34 L/kg | 1 – 2 hrs | 52% | 96.3% | 90% of the drug was eliminated in the urine | Thioether carboyxlic acid metabolite, Thioether glucuronide metabolite, Sulfone metabolite |