What is an antibiotic?

Potential sites of action are innumerable for selective toxicity of antibiotics to bacterial cells and not to host cells. Available antibiotics are effective by inhibiting synthesis of cell walls, protein, RNA, DNA, or folic acid. Both selective toxicity of antibiotics and resistance to antibiotics depend on the site of action and delivery to the site of action in adequate concentrations. Critical mechanisms for the transport of antibiotics through bacterial barriers and important pharmacokinetic attributes in humans are involved. Adverse effects of antibiotics may be immunologic or nonimmunologic. Nonimmunologic adverse effects of antibiotics are rarely related to slippage in the selectivity of toxicity but are usually the result of unrelated biochemical effects associated with other undesired actions of all drugs. Such undesired side effects can be avoided in drug development only if we understand the biochemical basis of these actions.