this is far more of an accidental Jekyll and Hyde story than an accidental vampire story. I don't even think the word "vampire" is used in the movie at all. except to discuss the actual bats, that is. in fact, it bears a closer resemblance to Atom Age Vampire (1963) than to anything with Dracula in the title.
Dr. Paul Beecher accidentally takes some pills that Dr. Matthew Campbell has been experimenting with. these have been treated with vampire bat blood. nothing good in the movies ever happens with vampire blood, so you can imagine what will happen if anyone takes the pills.
they are highly addictive, and they also have a propensity to release a scaly beast that kills innocent people. this ends exactly how one might think it does, but the ride there is pretty good. one of the cool things is seeing old LA in the background of the movie, and the nicely shot exteriors.
the actors are all good, and the story moves along pretty logically. you feel sorry for Paul (John Beal) as he slowly figures out what is going on with him. the makeup for the "vampire" is interesting, as it's kind of scaly and I can't tell if there are fangs in his mouth or not. it's always nice to see genre stalwart Kenneth Tobey as well, playing the sheriff here.
so if you have about 80 minutes or so to spare it's worth a look. just don't expect traditional vampires (or even sparkly ones).