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This document discusses principles of antibiotic classification and use. It begins by defining antibiotics and outlining their importance as well as risks of misuse. It then categorizes antibiotics as bactericidal or bacteriostatic and discusses antibiotic susceptibility testing. Various classification schemes are provided based on antibiotic mechanisms of action, including inhibiting bacterial cell wall synthesis, increasing membrane permeability, and interfering with protein or nucleic acid synthesis. The development of antibiotic resistance and methods to delay its emergence are also summarized.
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- 1. Principles of antibiotic andbasic classification 16th /feb/2015
- 2. introduction • Antibiotics aresubstances produced by various microorganisms, or synthetic agents, that suppress growth of other microorganisms. • Among the most prescribed drugs. • Proper use can be life saving • Indiscriminate use causes more: – Cost of h/care, – Side effects – Drug interactions – Foster emergence of drug resistance
- 3. Principle of antibiotic •Selectivity – Selectivty8 toxicity9 • Therapeutic index – Toxic dose/ Effective dose • Categories of antibiotics – Bactericidal • Usually antibiotic of choice – Bacteriostatic • Duration of treatment sufficient for host defenses
- 4. cont • Antibiotic susceptibilitytesting (in vitro) – Minimum inhibitory concentration (MIC) • Lowest concentration that results in inhibition of visible growth – Minimum bactericidal concentration (MBC) • Lowest concentration that kills 99.9% of the original inoculum
- 5. cont • Combination therapy –Prevent emergence of resistant strains – Temporary treatment until diagnosis is made – Antibiotic synergism • Penicillins and aminoglycosides • CAUTION: Antibiotic antagonism – Penicillins and bacteriostatic antibiotics • Antibiotics vs chemotherapeutic agents vs antimicrobials
- 6. Classification of antibioticby mechanism of action • 1) Drugs that inhibit bacterial wall synthesis or activate enzymes that disrupt the cell wall. • 2) Drugs that increase cell membrane permeability (causing leakage of intracellular material) • 3) Drugs that cause lethal inhibition of bacterial protein synthesis. • 4) Drugs that cause nonlethal inhibition of protein synthesis (bacteriostatics). • 5) Drugs that inhibit bacterial synthesis of nucleic acids
- 7. CONT • 6) Antimetabolites(disruption of specific biochemichal reactions-->decrease in the synthesis of essential cell constituents). • 7) Inhibitors of viral enzymes. • Acquired resistance to Antimicrobial drugs. • Mechanisms: • 1) Microbes may elaborate drug -metabolizing enzymes (ie penicillinase).
- 8. CONT • 2) Microbesmay cease active uptake of certain drugs • 3) Microbial drug receptors may undergo change resulting in decreased antibiotic binding and action. • 4) Microbes may synthesize compounds that antagonize drug actions.
- 9. CONT • How isresistance acquired? • A) Spontaneous mutation • B) Conjugation • Use of antibiotics PROMOTES the emergence of drug-resistant microbes. • Suprainfection (or supeinfection) : a new infection that appears through the course of treatment for a primary infection.
- 10. CONT • Delaying theemergence of resistance: • 1) Use antimicrobial agents only when needed. • 2) Use narrow-spectrum antibiotics whenever possible. • 3) Newer antibiotics should be reserved for situations in which older drus are dangerous or no longer effective.
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- 12. PROTEINS SYNTHESIS 30S 1 3 2GTP 1 2 3 GTP Initiation Factors mRNA 3 1 2 GTP 30S Initiation Complex f-met-tRNA Spectinomycin Aminoglycosides 1 2 GDP + Pi 50S 70S Initiation Complex AP