Rats

Ok, I've given up searching, so now I'm asking and I truly believe that at least one of you will know the answer to this.

I'm trying to recall the name of an old (70's or most likely 80's) movie in which a giant, seemingly smart rat has invaded a man's home. His wife and daughter go on vacation visit the grandmother and he begins the exterminating process. Oh wait, scratch that. The man becomes psychotically obsessed with getting rid of this rat which he knows is taunting him because this is a special designer rat.

So the entire movie is about the lengths to which this obsessed man will go to kill this rat.

Any ideas?

EDIT: It is not she short story from the movie Nightmares, before anyone makes that suggestion. This is a full-length movie and it is one rat versus one man.