The present invention provides a stable 2-(2-pyridylmethyl) sulfinyl-1H-benzimidazole (lansoprazole) comprising either greater than 500 ppm and not more than about 3,000 ppm water or greater than 200 ppm and not more than about 5,000 ppm alcohol, or both. The present invention provides a method of preparing a stable lansoprozole as well as a pharmaceutical composition containing same. The present invention further provides a method of purifying lansoprazole that is substantially free of sulfone and sulfide derivatives.
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