From what I've seen, a medkit needs to be held in order to view and manipulate it's contents.
When I attempt to drag an alternate medkit into the "hands" window it continues to display the contents of the original medkit despite the inventory window indicating that I have the alternate medkit in my hands.

It's possible that I'm doing something wrong but it would be very convenient to be able to switch between which medkit is being held as easily as which item is being held.