My Dr. has prescribed Omeprazole 40 mg twice per day - which has been effective for me. On the last refill, I noticed that some were marked R159 and some were significantly smaller and marked R645. When I questioned the pharmacy, they switched them out to the R159s. Most recent refill is all the R645s. They claim there is no difference other than in the "filler". Why are 2 different capsules made? Why would I ever WANT the "filler", and what is the REAL difference in the 2 capsules?