6. Antimicrobial Agents Flashcards
What is an antibiotic?
A chemical substance produced by microorganisms or chemical synthesis that, in low concentrations, inhibit the growth of other microorganisms
What are the criteria that have to be met in order for an antibiotic to be used?
Selective toxicity No allergic reactions Soluble in body fluids Capable of penetrating infected tissue Do not readily develop resistance
What is broad spectrum vs. Narrow spectrum?
Broad - affects both gram negative and gram positive bacteria
Narrow - affecting only gram negative OR gram positive
What is bactericidal vs. bacteriostatic?
Bactericidal - kills the bacteria
Bacteriostatic - prevents bacteria from multiplying
What is an antimicrobial agent?
A type of chemotherapeutic agent used specifically for the treatment of infectious diseases
Most are antibiotics
What are the different types of mode of action?
Inhibitors of:
- cell wall synthesis
- protein synthesis
- DNA and RNA synthesis
- cell membrane function
- other metabolic processes
What are beta-lactam antibiotics?
Antimicrobials that inhibit cell wall synthesis
What are the two major groups of beta-lactam antibiotics?
Penicillins
Cephalosporins
What is the prototype compound for natural penicillins?
Penicillin G or Benzylpenicillin
What is the spectrum for natural penicillins?
Narrow
Gram positive
What is the resistance to natural penicillins?
Are inactivated or sensitive to the enzyme Beta-lactamase, which opens the beta-lactam ring making the antibiotic useless
What is the clinical use for natural penicillins?
Penicillin G destructive to gastric acid and cannot be taken orally
Penicillin V can be taken orally
Are often given in combination with other drugs to improve absorption and retention abilities
Does class concept apply to natural penicillins?
Yes, test results from one antibiotic apply to all antibiotics of that class
What are the semisynthetic beta-lactamase resistant penicillins?
Oxacillin
Methicillin
Cloxacillin
Mainly used to treat staphylococcal infections, have a narrow gram positive spectrum Cloxacillin commonly used, more stable, class concept applies
What is the bacterial resistance to semisynthetic penicillins?
Is due to altered penicillin binding proteins in their cell walls that prevent the antibiotic from binding
What are the aminopenicillins?
Ampicillin
Broad spectrum, both gram positive and negative
Susceptible to beta-lactamase
Amoxicillin used clinically as it has better absorption and excretion
Class concept applies
What are anti-pseudomonal penicillins?
Primarily directed towards the resistant psedudomonas aeruginosa
Broad spectrum
Inactivated by staphylococcal beta-lactamase
Expensive, used if other antibiotics are resistant
Class concept does not apply
What are the two groups of anti-pseudomonal penicillins?
Carboxy penicillins
- carbenicillin
Ureidopenicillins
- mezlocillin, azlocillin
What are the two agents used, that when given in combination with beta-lactam antibiotics, the beta-lactamase enzyme is inhibited?
Clavulanic acid eg. Amoxicillin-clav, Ticarcillin-clav
Sulbactam
What are cephalosporins?
A beta-lactam antibiotic
First produced from a fungus
Broad spectrum
What is the first generation of cephalosporins?
Include cephlaothin, cefazolin, cephalexin
More expensive
Class concept generally applies
Injected, but cephalexin can be taken orally
What is the second generation of cephalosporins?
Includes cefaclor, cefonicid, cefotiam, cefotetan, cefamandole, ceforanide
Broad spectrum, increased against gram negative but decreased against gram positive
None are effective against pseudomonas
Class concept does not apply
What is the third generation of cephalosporins?
Include cefixime, cefotaxime, ceftizoxime, cefoperazone, cefazidime, ceftriaxone
Broad spectrum, less against gram positives but more against enterobacteriaceae and pseudomonas
Class concept does not apply
What is the fourth generation of cephalosporins?
Includes cefipime, cefipriome
Broad spectrum
Selection for antimicrobial susceptibility testing varies
What is Aztreonam?
Other beta-lactam antibiotic
Attaches to penicillin binding proteins and disrupts cell wall synthesis
Ineffective against gram positives
Effective against enterobacteriaceae and psudomonas that are resistant to other antibiotics
What is imipenem?
Belongs to a class called carbapenems Bactericidal - binds to proteins of the cell wall causing bacterial cells to elongate and lyse Broad spectrum
What is Vancomycin?
NOT a beta-lactam antibiotic but still inhibits cell wall synthesis
Belongs to a class called glycopeptides
Not affected by beta-lactamase
Bactericidal
Narrow gram positive spectrum
Used to treat when other antibiotics are resistant
Have toxic side effects such as hearing loss
What are the four groups of antibiotics that inhibit bacterial protein synthesis?
Macrolide
Chloramphenicol
Tetracyclines
Aminoglycosides
What is erythromycin?
Belongs to the group macrolides
Binds to ribosomal sub units
Usually bacteriostatic
Narrow mainly gram positive spectrum, some gram negatives
What is clindamycin?
Similar to Erythromycin
Better absorption and penetration properties
Better for treating anaerobic infections
Associated side effect of diarrhea
What is Chloramphenicol?
Bacteriostatic, inhibits protein synthesis
Broad spectrum
Small molecule
Serious toxic effects - gray syndrome in infants, aplastic anemia, dose-related marrow depression
Used for treatment of typhoid and meningitis
What are Tetracyclines?
Inhibit protein synthesis, prevent the binding of tRNA to mRNA Bacteriostatic Broad spectrum Resistance is common Treats chlamydia, acne, mycoplasma Taken orally, not given to children
What are Aminoglycosides?
Inhibit protein synthesis, bactericidal
Ineffective in treating anaerobic infections
Synergistic action with beta-lactum antibiotics
Movement affected by magnesium and calcium ions
Broad spectrum
Toxic to kidneys, damage to eights cranial nerve
What are some Aminoglycosides currently in use?
Kanamycin Gentamicin Tobramycin Amikacin Netilmicin Spectinomycin Class concept does not apply
What are some antimicrobials that inhibit DNA and RNA synthesis?
Fluoroquinolones
Nalidixic Acid
Metronidazole (Flagyl)
What are Floroquinolones?
Belong to a class called Quinolones
Bind to DNA gyrase enzymes, inhibit nucleic acid synthesis
Bactericidal
Broad spectrum including enterobacteriaceae
Toxic - irreversible cartilage and skeletal damage
What is Nalidixic Acid?
Belong to the class Quinolone
Broad spectrum
Treats urinary tract infections
What is Metronidazole?
Effective against anaerobic infections
Breaks up DNA strands - bactericidal
Treats protozoan parasitic infections
What are Polymyxins?
Inhibits cell membrane function Belong to polypeptides Bind to cell membranes causing leakage of cell contents - bactericidal Toxic - kidneys and nerves Narrow gram negative spectrum
Include polymixin B and polymixin E
What are some antimicrobial agents that inhibit other metabolic cell processes?
Sulfonamides
Trimethoptim
Nitrofurantoin
What are Sulfonamides?
Antimicrobial agents NOT antibiotics Synthetic Prevent the synthesis of folic acid, work by competitive inhibition Bacteriostatic Broad spectrum, inexpensive Treat urinary infections Synergistic action with trimethoprim
What is Trimethoprim?
Interferes with folic acid, using competitive inhibition
Broad spectrum
Often used with sulfonamide and the combination is called cotrimoxazole
Used for urinary tract infections
What is Nitrofurantoin?
Synthetic
Belongs to a group called Nitrofurans
Mode of action not clear - may damage DNA, protein, translation enzyme
Broad spectrum
Treats urinary tract infections
Can be both bactericidal and bacteriostatic
