Half of the subjects will receive Gleevec® alone on Day 1 and Gleevec® and calcium carbonate on Day 15, and the other half will receive Gleevec® and calcium carbonate on Day 1 and Gleevec® alone on Day 15, determined by randomization of subjects receiving either the combination or Gleevec® alone during the first visit. Doses will be 400 mg Gleevec® and 4000 mg calcium carbonate (4 x Tums Ultra 1000® chewable tablets, equivalent to 4000 mg calcium carbonate or 1600 mg calcium.