Formulations are dry blended for 15 min in a Patterson Kelley twinshell blender, and tablets are prepared via direct compression on a Stokes F press with 1/2-in. standard round concave punches to an initial hardness of 5 or 8 kg using a Pfizer hardness tester. Hardnesses are determined at 0, 2, 4, 6, 8, 12, and 26 weeks for tablets stored at 445'C; and at 0, 2, 4, 6, 8, 12, 26, 52, 78, 104, and 156 weeks at 23'C. Any tablets reaching a hardness beyond the limits of the hardness tester are assigned a hardness of 20+ kg.