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Pharmacology: Pantoprazole is a proton pump inhibitor. It accumulates in the acidic compartment of parietal cells and is converted to the active form, a sulfanilamide, which binds to hydrogen-potassium-ATP-ase at the secretory surface of gastric acid production, leading to inhibition of both basal and stimulated acid secretion. The duration of inhibition of acid secretion does not correlate with the much shorter elimination half-life of pantoprazole.
Pharmacokinetics: Absorption: Rapidly absorbed. However, absorption may be delayed up to 2 hours or more if pantoprazole is taken with food. Bioavailability (oral) 77%.
Distribution: Vd: Following intravenous administration to extensive metabolizers: 0.17 L per kg (11 to 23.6 L).
Protein binding: Very high (98%), primarily to albumin.
Biotransformation: Hepatic, extensive. The major enzyme involved in the metabolism of pantoprazole is the polymorphically expressed cytochrome P450 isoform S-mephenytoin hydroxylase, also known as CYP2C19. The primary metabolite is the conjugate desmethvlpantoprazole. Some patients who are deficient in this enzyme system will be slow metabolizers of pantoprazole. Patient who are slow metabolizers (3% of Caucasians of African-Americans; 17% to 23% of Asians) can produce plasma concentrations 5 times or more higher than patients with the enzyme present.
Half-life: Elimination-following oral or intravenous administration; 1 hour.
The half-life of pantoprazole is prolonged (7 to 9 hours) in patients with cirrhosis of the liver and in genetically determined slow metabolizers (3.5 to 10 hours).
Elimination: Renal 71%, fecal 18% (biliary excretion). Dialysis removes insignificant amounts of pantoprazole.
