Antimicrobial agents The goal of antimicrobial chemotherapy Administer a drug to an infected person that  Destroys the infective agent  Without harming the host’s cells 2 Characteristics of the Ideal Antimicrobial Drug  Selectively toxic to the microbe but nontoxic to host cells  Microbicidal rather than microbistatic  Relatively soluble; functions even when highly diluted in body fluids  Remains potent long enough to act and is not broken down 3 Characteristics of the Ideal Antimicrobial Drug  Doesn’t lead to the development of antimicrobial resistance Remains active in tissues and body fluids  Readily delivered to the site of infection  Does not disrupt the host’s health by causing allergies or predisposing the host to other infections 4 Terminology of Chemotherapy Chemotherapeutic drug Any chemical used in the treatment, relief, or prophylaxis of a disease Prophylaxis Use of a drug to prevent imminent infection of a person at risk Antibiotics Substances produced by the natural metabolic processes of some microorganisms that can inhibit or destroy other microorganisms 5 Terminology of Chemotherapy Semi synthetic drugs Drugs which are chemically modified in the laboratory after being isolated from natural sources Synthetic drugs The use of chemical reactions to synthesize antimicrobial compounds in the laboratory 6 Terminology of Chemotherapy Narrow spectrum (limited spectrum) Antimicrobials effective against a (limited spectrum) limited array of microbial types for example, a drug effective mainly on gram-positive bacteria Broad spectrum (extended spectrum) Antimicrobials effective against a (extended spectrum) wide variety of microbial types for example, a drug effective against both gram- positive and gram-negative bacteria 7 Terminology of Chemotherapy Combined therapy Where two or more drugs are given simultaneously, either to prevent the emergence of resistant species or achieve synergism Microbicidal Microbistatic Minimum inhibitory concentration (MIC) Lowest antibiotic concentration that inhibits growth of bacteria Minimum bactericidal concentration (MBC) Lowest antibiotic concentration that kills 99.9% of population. Mechanisms of Drug Action  Inhibition of Cell Wall Synthesis  Inhibition of Protein Synthesis  Inhibition of Nucleic Acid Synthesis  Antimetabolite Mechanisms of Drug Resistance 1- Preventing entrance of the drug  Many gram-negative bacteria 2- Pump the drug out of the cell after it has entered 3- Inactivating drugs through chemical modification 4- Changing the antibiotic target Basic sites of antibiotic activity