2. introduction
• Antibiotics are substances 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 susceptibility testing (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 antibiotic by
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) Microbes may 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 is resistance 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 the emergence 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.
