Pantopraz Mechanism of Action

Pharmacology: Pantoprazole is a substituted benzimidazole which inhibits the secretion of hydrochloric acid in the stomach by specific action on the proton pumps of the parietal cells.
Pantoprazole is converted to its active form in the acidic environment in the parietal cells where it inhibits the H⁺, K⁺ ATPase enzymes ie, the final stage in the production of hydrochloric acid in the stomach. The inhibition is dose-dependent and affects both basal and stimulated acid secretion. As with other proton-pump inhibitors and H₂-receptor inhibitors, treatment with pantoprazole causes a reduced acidity in the stomach and thereby an increase in gastrin in proportion to the reduction in acidity. The increase in gastrin is reversible. Since pantoprazole binds to the enzyme distal to the cell receptor level, the substance can affect hydrochloric acid secretion independently of stimulation by other substances (acetylcholine, histamine, gastrin). The effect is the same whether the product is given orally or intravenously.
Pharmacokinetics: Pantoprazole is rapidly absorbed and the maximal plasma concentration is achieved even after 1 single 40-mg oral dose. On average at about 2.5 hrs post dose the maximum serum concentrations of about 2-3 mcg/mL are achieved, and these values remain constant after multiple administration. Volume of distribution is about 0.15 L/kg and clearance is about 0.1 L/hr/kg. Terminal half-life is about 1 hr. There were few cases of subjects with delayed elimination. Because of the specific activation of pantoprazole in the parietal cell, the elimination half-life does not correlate with the much longer duration of action (inhibition of acid secretion). Pharmacokinetics does not vary after single or repeated administration. In the dose range of 10-80 mg, the plasma kinetics of pantoprazole are virtually linear after both oral and IV administration.
Pantoprazole's serum protein-binding is about 98%. The substance is almost exclusively metabolized in the liver. Renal elimination represents the major route of excretion (about 80%) for the metabolites of pantoprazole, the rest are excreted with the feces. The main metabolite in both the serum and urine is desmethylpantoprazole, which is conjugated with sulfate. The half-life of the main metabolite (about 1.5 hrs) is not much longer than that of pantoprazole.
Bioavailability: Pantoprazole is completely absorbed after oral administration. The absolute bioavailability from the tablet was found to be about 77%. Concomitant food intake had no influence on AUC, maximum serum concentration and thus bioavailability. Only the variability of the lag-time will be increased by concomitant food intake.
Characteristics in Patients/Special Groups of Subjects: No dose reduction is requested when pantoprazole is administered to patients with restricted kidney function (including dialysis patients). As with healthy subjects, pantoprazole's half-life is short. Only very small amounts of pantoprazole are dialyzed. Although the main metabolite has a moderately delayed half-life (2-3 hrs), excretion is still rapid and thus accumulation does not occur. Although for patients with liver cirrhosis (classes A and B according to Child) the half-life values increased between 7-9 hrs and the AUC values increased slightly by a factor of 5-7, the maximum serum concentration only increased slightly by a factor of 1.5 compared with healthy subjects. A slight increase in AUC and C_max in elderly volunteers compared with younger counterparts is also not clinically relevant.