The first trailer is the international one. It gives away a little to much of the plot/gore, but it's still great fun to watch.
The second is made for the American market and focuses very much on a very mad doctor doing human experiments... it's not a "mad doctor" film, it's a zombie (and cannibal) film.
What is interesting here, is to see how different the films were promoted. The international trailer show what the film is really about, but the American gives the viewer a completely wrong impression of what the film is about. Check them out:
Zombie Holocaust, 13,9Mb.
Doctor Butcher M.D (Medical Deviate), 7,78Mb.
Also, check out this poster for Doctor Butcher. Goes along with the same theme as the trailer.
I found this poster over at The Poster Pit. Lots of cool posters from many different genres. Check it out!