I'm not at Derxel, but it's been my experience at my medical school that unless the instructor specifically tells you that test questions are coming from the text book, you can pretty much ignore the so-called required reading.
There are all sorts of reading that are required. Usually this is wishful thinking on the part of the faculty. Study your notes and maybe get some good review books and you'll do just fine.
The reading load can be tremendous, but isn't always necessary. Almost every professor likes to feel important and will "require" a lot from you. This becomes interesting when you have multiple courses competing for your time. It is up to you to be the material filter. For most medical school classes, lecture transcripts, handouts, and review books are enough to do well. Big texts can usually be used for reference, but can be avoided for daily reading.
For some classes, you will have to read everything, and your 2nd years can advise you there. Just keep in mind that when you are covered up, it is likely that everyone is just as overwhelmed as you. Grading in medical school is usually relative, so often the goal it simply to keep up with the pack.
I am not familiar with Drexel. Is it a problem-based school? If so, then this is customary for any problem-based school.
We were assigned primary reading each phase (anywhere from 800-2200 pages in 4-7 weeks). Test questions can come from any of those pages, although the professors usually ask questions based on their learning objectives. So you read all of the material and concentrate on the objectives. Many students (including myself) just read the primary reading and didn't pay attention to the objectives. There were so many objectives that you would waste time just trying to figure out what you did and didn't need to know. Almost always they would require you to learn everything.
It's not as bad as it sounds. Remember, concentrate on the big concepts. 70-80% of the questions will center around main concepts and only 20-30% will be on minutia.