Chpt 20 Antimicrobial Drugs

Antimicrobial Drugs
Chapter 20


I History of Chemotherapy
II Spectrum of Antimicrobial Activity
III Action of Antimicrobial Drugs
A. Bactericidal
B. Bacteriostatic
C. Inhibition of Cell wall synthesis
1. Peptidoglycan: alternating NAM and NAG subunit chains that are held together by peptide bridges.
a. When reproducing and growing, bacteria must synthesize more NAG/NAM units to add.
2. Antibiotic types ( Natural Beta – lactams): Prevent cross-linkage of NAM subunits
a. penicillin: narrow spectrum, kills only gram +
b. methicillin: works on some gram -
c. cephalosporin: works on some gram -
d. vancomycin: works on gram +
e. bacitracin: works on gram +
f. isoniazid: block mycolic acid addition to cell walls as well as peptidoglycan production
D. Inhibition of Protein synthesis
1. Ribosomes: The major structure of a cell that caries out protein synthesis
a. eukaryotic: 80s ribosomes
b. prokaryotic: 30s + 50s ribosomes = 70s
2. Antibiotic types
a. aminoglycosides:
i. streptomycin: change the shape of the 30s subunit
ii. gentomycin: change the shape of the 30s subunit
iii. tetracycline: prevent amino acids from entering the ribosome at the 30s subunit
b. chloramphenicol: blocks 50s ribosome, preventing peptide bond formation
c. macrolides:
i. bind to 50s ribosome
ii. prevent movement from one codon to the next, halting translation
iii. ex: erythromycin
E. Injury to the Plasma Membrane (Disruption of cytoplasmic membranes)
1. plasma membranes: phospholipids bi-layers that contain sterols (lipids)
a. polymyxin: disturbs phospholipids bi-layers
i. effective against gram – (Pseudomonas)
ii. toxic to kidneys and is usually used for external pathogens
2. Fungi contain a sterol called ergosterol, humans = cholesterol
3. Antifungal drugs:
a. polyenes: attach to ergosterol in the membrane
b. azoles: inhibit ergosterol synthesis
F. Inhibition of Nucleic Acid (DNA/RNA) Synthesis 21, 22, 23
G. Inhibiting the Synthesis of essential metabolites (anti-metabolic agents/inhibit metabolism) 17
1. Metabolism: all of the chemical reactions within a cell used to store or release energy
a. organisms often have unique metabolic pathways
b. most narrow antibiotic
2. Sulfonamides
a. Para-Aminobenzoic acid (PABA) 18, 19
H. Block attachment
I. Antifungal Drugs
J. Antiviral Drugs 20, 24
K. Antiprotozoan and Antihelminthic Drugs
IV Tests to Guide Chemotherapy
V Effectiveness of chemotherapeutic agents
VI Clinical considerations

Definitions:

Chemotherapy: the treatment of disease with chemicals (drugs) taken into the body.

Chemotherapeutic agents: drugs used for chemotherapy
Antimicrobial drugs: The class of chemotherapeutic agents used to treat infectious diseases.

Selective toxicity: killing the harmful organism without harming the host
1. The drug must be more toxic to a pathogen than a pathogen’s host.
2. possible due to difference in structure or metabolism between the pathogen and the host.

Synthetic drugs: synthesized in the laboratory

Antibiotics: produced by microorganisms, and in small amounts, inhibit another mo.
1. naturally occurring (Penicillin)
2. Semi-synthetic: slight alterations to naturally occurring agents