> the patentability of modifications to existing drugs under Indian law

A key point here is that the original drug itself was patented, and has expired. The issue that the Indian court had with Gleevec patent application is that it only rearranged the molecule in a new crystal pattern, ie Polymorphism. The Indian court consider polymorphism to be a well known technique when working with drugs, and just applying polymorphism to a old drug and record what it did do not fulfill the requirement for patentable.