Atomica agrees with you, wofa, but look what a medical dictionary has to say:
Antibiotic: A drug used to treat bacterial infections.

The original definition of an antibiotic was a substance produced by one microorganism that selectively inhibits the growth of another microorganism. However, wholly synthetic antibiotics (usually chemically related to natural antibiotics) have since been produced that accomplish comparable tasks.
http://www.medterms.com/script/main/Art.asp?li=MNI&ArticleKey=8121
Interesting: bio more or less means life, doesn't it, or alive? I guess the above usage is a transference, like using Kleenex as the word to mean any brand of facial tissue, or Xerox for any copied piece of paper.