That's a good question to ask your pharmacist or your doctor.  It
probably depends in part on the type of drug, the kind of coating, the
half-life, and so on.  In your case, you might be able to take your meds
immediately after you have your last bowel movement (if you can figure
out when that is) because generally once you are through with the prep,
your gut motility slows back down; that is, there wouldn't be time for
your meds to make it from your stomach all the way to your colon before
the colonoscopy.  They're more concerned about you having a full bowel
and consuming things that could stain your bowel (like red jello).

Barb