Why does intake of penicillin not affect human human cells?

Because penicillin is a drug that kills bacteria by killing its cell wall.
However we humans are not plants and hence do not have cell wall. thus the penicillin does not have anything to kill. We humans have different Biochemical pathways.

antibiotics commonly block the biochemical pathways important for bacteria. many bacteria, for example make a cell wall to protect themselves. the antibiotic penicillin blocks the bacterial processes that build the cell wall. as a result, the growing bacteria become unable to make cell walls and die easily. human cells don't make a cell wall anyway, so penicillin cannot have such an effect on us.
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