Pantoprazole sodium, racemicsodium5-(difluoromethoxy)-2-[[3,4-dimethoxy-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazole sesquihydrate is a white tooff-white crystalline powder that is freely soluble in water,very slightly soluble in phosphate buffer at pH 7.4, and practicallyinsoluble in n-hexane. The benzimidazole of this drughas a weakly basic nitrogen (pyridine N, pKa 3.83) and an benzimidazoleproton (pKa 0.11), facilitating formulation as asodium salt. The stability of the compound in aqueous solutionis pH dependent; the rate of degradation increases with decreasingpH. At ambient temperature, the degradation half-lifeis approximately 2.8 hours at pH 5.0 and approximately 220hours at pH 7.8. The absorption of pantoprazole is rapid (Cmax of2.5μg/mL, Tmax 2.5 hours) after single or multiple oral40-mg doses. Pantoprazole is well absorbed (77% bioavailability).Administration with food may delay its absorptionbut does not alter pantoprazole bioavailability. Pantoprazoleis distributed mainly in extracellular fluid. The serum proteinbinding of pantoprazole is about 98%, primarily to albumin.Pantoprazole is extensively metabolized in the liver throughthe CYP system, including O-demethylation (CYP2C19),with subsequent sulfation. Other metabolic pathways includesulfur oxidation by CYP3A4. There is no evidencethat any of the pantoprazole metabolites have significantpharmacological activity. Approximately 71% of a dose of pantoprazole is excreted in the urine, with 18% excretedin the feces through biliary excretion.
