I've got to disagree with Tank on this one. Telling Lois might waste even more precious time. There's an entire package of emotions- anger, betrayal, more anger, that come with the revelation that her partner has been lying to her. Lois needs to be on top of her game, and Clark can't afford to tell her for fear that in her distraction she'll miss something vital. He can't afford to tell her until after the antidote is found.
