introduction to antimicrobial agents. definition: use of drugs to combat infectious diseases and...
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Introduction to antimicrobIntroduction to antimicrobial agentsial agents
Definition: Use of drugs to combat infectious diseases and cancer.
Antimicrobial drug ( 抗微生物药 )
Antiparasitic drug( 抗寄生虫药 )
Anticancer drug ( 抗癌药 )
1. Chemotherapy,化学治疗
Antimicrobial drugAntimicrobial drug
Antimicrobial drugs either kill microbes (microAntimicrobial drugs either kill microbes (microbicidal) or prevent the growth of microbes (micbicidal) or prevent the growth of microbes (microbistatic).robistatic).
AntibacterialAntibacterial
AntiviralAntiviral
AntifungalAntifungal
AntiparasiticAntiparasitic
Antimicrobial ChemotherapyAntimicrobial Chemotherapy
Differential toxicity: based on the concept that the Differential toxicity: based on the concept that the drug is more toxic to the infecting organism than to drug is more toxic to the infecting organism than to the hostthe host
Majority of antibiotics are based on naturally Majority of antibiotics are based on naturally occurring compoundsoccurring compounds
or may be semi-synthetic or syntheticor may be semi-synthetic or synthetic
What is the ideal antibioticWhat is the ideal antibiotic
Have the appropriate spectrum of activity for the clinical Have the appropriate spectrum of activity for the clinical
setting.setting.
Have no toxicity to the host, be well tolerated.Have no toxicity to the host, be well tolerated.
Low propensity for development of resistance.Low propensity for development of resistance.
Not induce hypersensitivies in the host.Not induce hypersensitivies in the host.
What is the ideal antibioticWhat is the ideal antibiotic
Have rapid and extensive tissue distributionHave rapid and extensive tissue distribution
Have a relatively long half-life.Have a relatively long half-life.
Be free of interactions with other drugs.Be free of interactions with other drugs.
Be convenient for administration.Be convenient for administration.
Be relatively inexpensiveBe relatively inexpensive
DefinitionsDefinitions
Spectrum of ActivitySpectrum of Activity: : Narrow spectrum - drug is effective against a limited Narrow spectrum - drug is effective against a limited number of speciesnumber of species
Broad spectrum - drug is effective against a wide Broad spectrum - drug is effective against a wide variety of speciesvariety of species
Gram negative agentGram negative agentGram positive agentGram positive agentAnti-anaerobic activityAnti-anaerobic activity
DefinitionsDefinitions
Minimum Inhibitory Concentration (MIC)Minimum Inhibitory Concentration (MIC)- minimum concentration of antibiotic required to inhibit the - minimum concentration of antibiotic required to inhibit the growth of the test organism.growth of the test organism.
Minimum Bactericidal Concentration (MBC)Minimum Bactericidal Concentration (MBC)- minimum concentration of antibiotic required to kill the test - minimum concentration of antibiotic required to kill the test organism.organism.
Bacteriostatic Bacteriostatic
BactericidalBactericidal
DefinitionsDefinitions
Chemotherapeutic Index ( CI ): LDChemotherapeutic Index ( CI ): LD5050/ED/ED50 50 or LDor LD55/ED/ED9595
PAE (Post antibiotic effect): PAE (Post antibiotic effect): the continued suppression the continued suppression of antibacterial growth after the administration of of antibacterial growth after the administration of antibiotic has ceased and serum concentrations have antibiotic has ceased and serum concentrations have fallen below the minimum inhibitory concentration .fallen below the minimum inhibitory concentration .
病原微生物病原微生物抗微生物药抗微生物药抗菌作用抗菌作用
耐药性耐药性
抗病能力
抗病能力
致病作用
致病作用 不良反应
不良反应
体内过程
体内过程
机 体机 体
Five modes of antimicrobial actionFive modes of antimicrobial action
(i) Inhibition of cell wall synthesis(i) Inhibition of cell wall synthesis(ii) Disruption of cell membrane function(ii) Disruption of cell membrane function(iii) Inhibition of protein synthesis(iii) Inhibition of protein synthesis(iv) Inhibition of nucleic acid synthesis (iv) Inhibition of nucleic acid synthesis (v) Action as antimetabolites(v) Action as antimetabolites
PeptidoglycanPeptidoglycan
The glycan backbone The glycan backbone
Peptidoglycan cross-bridgesPeptidoglycan cross-bridgesTetrapeptide
side chainTetrapeptide
side chain
Targets of antimicrobial drugsTargets of antimicrobial drugs
————Disruption of cell membrane functionDisruption of cell membrane function————
————Disruption of cell membrane functionDisruption of cell membrane function————
PolymyxinPolymyxin
CationicCationic and alters cytoplasmic membrane lters cytoplasmic membrane
permeability by binding to a negatively charpermeability by binding to a negatively char
ged site in the lipopolysaccharide layerged site in the lipopolysaccharide layer
Amphotericin BAmphotericin BAssociates with ergosterol, the main cAssociates with ergosterol, the main component of fungal cell membranesomponent of fungal cell membranes
Associates with ergosterol, the main cAssociates with ergosterol, the main component of fungal cell membranesomponent of fungal cell membranes
Drugs that disrupt cell membrane Drugs that disrupt cell membrane functionfunction
Inhibition of protein synthesisInhibition of protein synthesis
Generally work at different stages of prokaryotic mRNA tGenerally work at different stages of prokaryotic mRNA translation into proteins, like initiation, elongation ranslation into proteins, like initiation, elongation (includin(including g aminoacyl tRNA entry, proofreading, peptidyl transfer a entry, proofreading, peptidyl transfer a
nd ribosomal translocation) and terminationnd ribosomal translocation) and termination.).)
The antibiotic only affects 70S ribosomes in the bacteria The antibiotic only affects 70S ribosomes in the bacteria and does nothing for the 80S ribosomes in human.and does nothing for the 80S ribosomes in human.
Inhibition of protein synthesisInhibition of protein synthesis
MacrolidesMacrolides
LincomycinLincomycin
ChloromycetinChloromycetin
TetracyclinesTetracyclinesAminoglycosidesAminoglycosides
bind to 50sbind to 50s
bind to 30sbind to 30s
Inhibition the Synthesis of metabolitesInhibition the Synthesis of metabolites
Antibiotics that mimic the structure of the specific Antibiotics that mimic the structure of the specific substrate that the normal substrate is replaced and don’t substrate that the normal substrate is replaced and don’t have contact with the enzyme which acts on a substrate have contact with the enzyme which acts on a substrate to produce a certain metabolically important metabolite to produce a certain metabolically important metabolite inside the cell. inside the cell.
Action of sulfanilamide Action of sulfanilamide
QuinolonesQuinolones
Inhibit the DNA gyraseInhibit the DNA gyrase→ → Interfer with Interfer with DNA replication
RifampicinRifampicin
Inhibits DNA-dependent RNA polymeraseInhibits DNA-dependent RNA polymerase →mRNA↓→mRNA↓
—— Inhibitors of nucleic acid synthesis
———— Inhibitors of nucleic acid synthesis
——
Antimicrobial resistanceAntimicrobial resistance
ResistanceResistance: : the inability to kill or inhibit the organism the inability to kill or inhibit the organism with clinically achievable drug concentrations with clinically achievable drug concentrations
Resistance may be innate (naturally resistant)Resistance may be innate (naturally resistant)
Resistance may be acquiredResistance may be acquired - mutation - mutation - acquisition of foreign DNA - acquisition of foreign DNA
Antimicrobial resistanceAntimicrobial resistance
Factors which may accelerate the development of Factors which may accelerate the development of
resistanceresistance
- inadequate levels of antibiotics at the site of - inadequate levels of antibiotics at the site of
infectioninfection
- duration of treatment too short - duration of treatment too short
- overwhelming numbers of organisms - overwhelming numbers of organisms
- overuse / misuse of antibiotics - overuse / misuse of antibiotics
Antimicrobial resistanceAntimicrobial resistance
General mechanisms of resistance:General mechanisms of resistance:
Inactivation / destruction of antibioticInactivation / destruction of antibiotic Altered binding siteAltered binding site Altered permeabilityAltered permeability Efflux (pumps) mechanismsEfflux (pumps) mechanisms Bypass of metabolic pathwaysBypass of metabolic pathways
Resistance gene transmissionResistance gene transmission
Principles of use of antibacterial agentsPrinciples of use of antibacterial agents
Proper selection of an antibacterial agent is based on a nProper selection of an antibacterial agent is based on a number of factors.umber of factors.
The identity of the pathogenThe identity of the pathogen
The site of infectionThe site of infection
Pharmacokinetics (PK) Pharmacokinetics (PK)
Pharmacodynamics (PD) Pharmacodynamics (PD)
Potential toxicityPotential toxicity
Possible drug interactions, Possible drug interactions,
Cost, and convenience of administration.Cost, and convenience of administration.
Prophylaxis for infectionProphylaxis for infection
Prevention of Rheumatic Fever Prevention of Rheumatic Fever
Epidemic cerebrospinal meningitisEpidemic cerebrospinal meningitis Infective endocarditis Infective endocarditis
SurgerySurgery