Antibacterial drugs that inhibit nucleic acid synthesis sulphonamides. trimethoprim, quinolones and nitroimidazoles

Trimethoprim (hotiom left) acts on the same metabolic pathway as sulphonamides, but is an inhibitor of dihydrofolaie reductase (CD), h is selectively toxic because its affinity for the bacterial enzyme is 50 (KK) 

Rifanipiein prevents RNA transcription in many bacteria by inhibiting DNA-dependent RNA polymerase (htiiiom right). Resistance to rifampicin quickly develops but in combination with other drugs u is important in (he treatment of tuberculosis (Chapter 39). 

The use of chemicals to try and eradicate parasites, bacteria, viruses or cancer cells in the body is culled chemotherapy. It depends on the drufs being selectively toxic, i.e. toxic to the cells of the ptira-site. but not (too) toxic to the human host. Bacteria have many biochemical differences from human cells, and some amibaierial drags are strikingly non-ioxic to human.s. On the other hand, because cancer cells arc so simitar to normal cells, roost aniicancer drags show little. selective toxicity and therefore produce serious adverse effects (Chapter 43). 

Bacteriostatic agents inhibit bacterial growth, while bactericidal agents actually kill the organism. This distinction is not usually important clinically, as host-defence mechanisms are involved in the final elimination of bacterial pathogens. An exception is the treatment of infections in immunocompromised patients (AIDS, corticosteroids, aniicancer and immunosuppressant drags i. when a bactericidal agent should be used. 

1 Inactivating enzymes that destroy the drug. e.g. -lactamases produced by many staphylococci inaciivaie most penicillins and many cephalosporins. 

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Antibacterial drugs that inhibit nucleic acid synthesis sulphonamides, trimethoprim, quinolones and nitroimidazoles... 

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