A dosage form is provided for an anti-diabetic DPP-IV inhibitor of formula (I) as its tartarate salt, wherein the purity of the active pharmaceutical ingredient is maintained over a prolonged storage period under conditions similar to those likely encountered in home storage of the medication by a diabetic patient. A formulation free of calcium salts such as calcium phosphate, but including microcrystalline cellulose, copovidone, crospovidone, colloidal silicon dioxide, and magnesium stearate, when compacted into a tablet with the active pharmaceutical ingredient, was shown to be stable for at least six months at 40° C. and 75% relative humidity. Methods for preparation of the dosage form are also provided.
