Which pair of definitions correctly describes synergism and antagonism in the context of antibiotic combinations?

Synergism: two drugs always act on the same target molecule producing additive inhibition; Antagonism: two drugs always act on separate unrelated biochemical pathways producing no measurable interaction even if the drugs influence each other's uptake, metabolism, or targets.

Synergism: combined effect greater than expected from each drug alone; Antagonism: combined effect less than expected from each drug alone.

Synergism: a pharmacologic interaction where one drug completely blocks the action of the other so that only the first drug displays measurable activity in vitro or in vivo; Antagonism: when two drugs enhance each other to the point that their combined activity is multiplicative and always exceeds the sum of their individual activities, so doses must be increased to maintain an effect.

Synergism: one drug increases the toxicity of another without altering efficacy; Antagonism: one drug increases the efficacy of another while decreasing toxicity.