Antimicrobial Drugs Flashcards
Chemical used to treat diseases
Chemotherapeutic agents
A chemical used to destroy pathogenic
microorganisms with minimal damage
Produce naturally by organisms or created synthetically
Antimicrobial drugs
Antagonistic association between an organism and the metabolic substances produced by another
Antibiosis
Antimicrobial agent naturally produced by oragnisms
Antibiotic
“Magic Bullet”
Developed the concept of chemotherapy to treat microbial diseases
Paul Ehrlich
Developed by Ehrlich
First documented example of an antimicrobial drug
Salvarsan
Dicovered the first antibiotic, Penicillin
Alexander Fleming
Characteristics of Antimicrobial Agent
Selective toxicity Antimicrobial action Spectrum of activity Affects of antimicrobial combinations Tissue distribution, metabolism, and excretion of the medication Adverse effects Resistance to antimicrobials
Selectively toxic
Medically useful antimicrobials
The relative toxicity of a medication
The lowest dose toxic to the patient divided by the dose typically used for therapy
High would mean less toxic
Therapeutic index
Chemicals that inhibit growth of bacteria
Bacteriostatic
Chemicals that kill bacteria
Bactericidal
Affect a wide range of bacteria
Broad-spectrum antimicrobials
Affect only selected group of bacteria
Less distruptive to the normal microbiota
Norrow-spectrum antimicrobials
Advantage of broad-spectrum antimicrobials
Important for life-threatening diseases when intermediate antimicrobial treatment is essential and there is no time to culture and identify the pathogen
Disadvantage of broad spectrum antimicrobials
They disrupt normal microbiota
Affects of antimicrobial combinations
Antagonistic
Synergistic
Additive
Combinations that counter the effect of other antimicrobial agents
Antagonistic
Combinations in which the activity of one medication enhance the activity of the other
Synergistic
Combinations that are neither synergistic nor antagonistic
Additive
Adverse Effects
Allergic reactions
Toxic effects - damage kidney etc.
Suppresion of normal microbiota
Resistance to antimicrobials
Intrinsic (innate) resistance
Acquired resistance
Certain types of bacteria e.g. Mycoplasma
Intrinsic (innate) resistance
Due to spontaneuos mutation or the acquisition of new genetic information (horizontal gene transfer)
Acquired resistance
Actions of Antimicrobial Drugs
Inhibition of: Cell wall synthesis Protein synthesis Essential metabolite synthesis Nucleic acid replication and transcription
Inhibit enzymes that help from cross-links between adjacent glycan chains, ultimately leading to cell lysis
All have high therapeutic index
Beta-lactam antibiotics
Examples of beta-lactam antibiotics
Inhibit cell wall synthesis
Pencillins
Cephalosporins
Carbapenems
Monobactams
An enzyme that breaks the beta-lactam ring, destroying the activity of the antibiotic
Beta-lactamase
Examples of beta-lactamase
Inhibit cell wall synthesis
Penicillinases
Carbapenemases
Examples of penicillinase resistant penicillins
Methicillin
Dicl oxacillin
Resistant to methicillin
Only beta-lactam antibiotics effective against them are the newest cephalosporins
MRSA (Methicillin-resistant Staphylococcus aureus)
Low therapeutic index
Includes vancomycin
Glycopeptide antibiotics
Its toxicity limits its use to topical applications
Bacitracin
Antibacterial medication that inhibit protein synthesis
Aminoglycosides
Tetracyclines
Macrolides
Chloramphenicol etc.
Block the intiation of translation and cause misreading of mRNA
Aminoglycosides
Block the attachment of tRNA to the ribosome
Tetracyclines
Prevent the continuation of protein synthesis
Macrolides
Prevents peptide bonds from being formed
Chloramphenicol
Prevent the continuation of protein synthesis
Lincosamides
Interfere with the initiation of protein synthesis
Oxazolidinones
Prevents peptide bonds from being formed
Pleuromutilins
Each interferes with a distinct step of protein synthesis
Streptogramins
Antibacterial medications that inhibit nucleic acid synthesis
Fluoroquinolones
Rifamycins
Metronidazole
Inhibit topoisomerase enzyme which maintain supercoiling of DNA within the bacterial cell
Fluoroquinolones
Antibiotics that block bacterial RNA polymerase from initiating transcription
Rifamycins
Primarily used to treat tuberculosis
Rifampin
A synthetic compound that interferes with DNA synthesis and function, but only in anaerobic microorganisms
Metronidazole
Antibaterial medications that interfere metabolic pathways
Sulfa dugrs
Trimethoprim
Block different enzymes in a metabolic patyway required for nucleotide biosynthesis
Sulfa drugs
Trimethoprim
Meidcation used together as synergistic combination
Co-trimoxazole
Antibacterial medications that interfere with cell membrane intergrity
Daptomycin
Polymyxins
Effective only against gram positive
Daptomycin
Effective against gram negative cells
Polymyxins
Common ingredient in first-aid skin ointments
Polymyxin B
Antibacterial medication effective against mycobacterium tuberculosis
Isoniazid
Ethambutol
Pyrazinamide
Used to treat tuberculosis
First-line drugs
Used for strains resistant to first-line drugs
Second-line drugs
Inhibits the synthesis of mycolic acids
Isoniazid (INH)
Inhibits enzyme required for synthesis of other mycobacterial cell wall components
Ethambutol (EMB)
Interferes with a process that mycobacterial cells use to restart stalled ribosomes
Pyrazinamide (PZA)
Mechanism of action of antiviral drugs
Prevent viral entry Interfere with viral coating Interfere with nucleic acid syntheiss Prevent genome integration Prevent assembly and release of viral particles
Mechanisms of action of antifungal drugs
Interfere with: Cytoplasmic membrane synthesis and function Cell wall synthesis Cell division Nucleic acid synthesis
Antimicrobial susceptibility testing
Minimum inhibitory conc. (MIC)
Minimum bactericidal conc. (MBC)
Lowest conc. of a specific antimicrobial needed to prevent the growth of a bacterial strain in vitro
MIC
Lowest conc. of a specific antimicrobial that kills 99.9% of cells of a given strain of bacterial in vitro
MBC
Determines susceptibility of a bacterial strain to a variety of antimicrobial medications
Kirby-Bauer disc diffusion test
Conventional disc diffusion method
A gradient diffusion method that determines abtibiotic sensitivity and estimates MIC
Modification of disc difussion method
E test (for epsilometer)
Mechanisms of acquired resistance
Blocking entry
Inactivation of enzymes
Alteration of target molecule
Efflux of antibiotic
Resustance can be acquired through
Spontaneous mutation or horizontal gene transfer
Most common mechanism of transfer of antibiotic resistance genes is through
The conjugative transfer of R plasmids
Example of emerging resistance
CDC’s threat level: urgent
Colstridium difficile
Carbapenem-resistant Enterobacteriaceae (CRE)
Drug-resistant Neisseria gonorrhoeae
Example of emerging resistance
CDC’s threat level: serious
Candida Pseudomonas aeruginosa Non-typhoidal samonella Salmonella typhi Staphylococcus aureus
Lreventing resistance
Physicians prescription only when appropriate
Follow prescribe instructions when taking antimicrobials
Public must be educated