Depends on your school and depends on the class. At my school, just in MS1, we've had a lot of exposure to drugs. In our pharm class, we ran the gamut on a large variety of different classes of drugs. Something like 8 pages of excel spreadsheet. Had to know mechanism of action, sometimes chemical structure (such as beta lactams, the cephalosporins, etc), volume of distribution, BBB penetration, plasma protein binding when pertinent, how its eliminated, pertinent toxic effects. In our infectious disease class, for the chemotherapeutics, we had to know mechanism of resistance, spectrum of activity, and specific therapies for specific infections. Intramuscular shot of ceftriaxone + doxycycline for gonorrhea/chlamydia infection, etc.
As far as the boards, like L2D said, pick up a board review book. They've distilled out whats important for specific drugs in regards to USMLE.
Tangent: Don't you just love how in BS they teach us all of our drug knowledge in generic names, when in the actual practice of medicine the generic name is used in conversation maybe 10% of the time?