A long time ago, there were similar problems with injectable ivermectin (worm medicine) in horses. It also tended to colic the horses if they had a large parasite load, because it killed every worm instantly and the horse's digestive system took a big hit of dead and decaying parasites all at once . . . so they took it off the market and substituted an oral paste.
No, this was the feline leukemia vacc. Here is an article (altho it may be old, I didn’t keep up with how all of this turned out).
http://www.wgnradio.com/shows/pet/felinevaccines.htm
susie