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ANIBIOTICS AND CHEMOTHERAPUETIC AGENTS (I)
Antibiotics: Substances produced by living organisms and active against other living organisms, e.g. Penicillin, Chemotherapeutic agents: Substances not produced by living organisms, active against living organisms, e.g. INAH
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USES OF ANTIBIOTICS: @ Treatment of patients @ As selective agents in culture media, e.g.: VCNT @ To prevent contamination of tissue cultures to isolate viruses @ In sensitivity tests to select the drug suitable to treat an infection.
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Antibiotics in current use:
Classified as follows: @ Antibiotics against G+ve bacteria e.g.: penicillin. Exception Neisseria is sensitive and E.fecalis is resistant to penicillin @ Antibiotics against G-ve bacteria, e.g. streptomycin. Exception Mycobacteria sensitive and Neisseria resistant to streptomycin
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@ Antibiotics against both G-ve & G+ve
bacteria (broad spectrum antibiotics) e.g. tetracycline @ Antibiotics against fungi, e.g. Nystatin @ Bacteriostatic antibiotics: Prevent multiplication of bacteria, e.g.: erythromycin. @ Bactericidal antibiotics: Kill bacteria, e.g.: penicillin,
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Synergism: @ Two or more drugs are given together to patient to increase the effect of treatment. @ This combined therapy is indicated: * When organism isolated is slightly sensitive to any of these drugs
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* When more than one organism is
isolated and each has a different sensitivity. * To save life in severe infections * For diseases known to be treated by combined therapy, e.g.TB * To prevent development of resistance when drugs used are suspected to be resistant.
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Antagonism: @ One antibiotic may stop the action of the other when tested in vitro. @ The effect of the two is less efficient in killing the organism than using each drug separately.
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Synergism and Antagonism
@ Two from group (1) are synergistic never antagonistic. @ Two from group (2) are synergistic never antagonistic. @ One from group (1) and one from group (2): * If organism is sensitive to group (1), antagonism occurs. * If organism is resistant to group (1), synergism occur. (1) Bactericidal drugs (2) Bacteriostatic drugs Penicillin Tetracycline Streptomycin Chloramphenicol Kanamycin Sulphonamides Gentamycin Erythromycin
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