6. Antimicrobial Agents

Question 1

What is an antibiotic?

Answer 1

A chemical substance produced by microorganisms or chemical synthesis that, in low concentrations, inhibit the growth of other microorganisms

Question 2

What are the criteria that have to be met in order for an antibiotic to be used?

Answer 2

Selective toxicity
No allergic reactions
Soluble in body fluids
Capable of penetrating infected tissue
Do not readily develop resistance

Question 3

What is broad spectrum vs. Narrow spectrum?

Answer 3

Broad - affects both gram negative and gram positive bacteria

Narrow - affecting only gram negative OR gram positive

Question 4

What is bactericidal vs. bacteriostatic?

Answer 4

Bactericidal - kills the bacteria

Bacteriostatic - prevents bacteria from multiplying

Question 5

What is an antimicrobial agent?

Answer 5

A type of chemotherapeutic agent used specifically for the treatment of infectious diseases

Most are antibiotics

Question 6

What are the different types of mode of action?

Answer 6

Inhibitors of:

• cell wall synthesis
• protein synthesis
• DNA and RNA synthesis
• cell membrane function
• other metabolic processes

Question 7

What are beta-lactam antibiotics?

Answer 7

Antimicrobials that inhibit cell wall synthesis

Question 8

What are the two major groups of beta-lactam antibiotics?

Answer 8

Penicillins

Cephalosporins

Question 9

What is the prototype compound for natural penicillins?

Answer 9

Penicillin G or Benzylpenicillin

Question 10

What is the spectrum for natural penicillins?

Answer 10

Narrow

Gram positive

Question 11

What is the resistance to natural penicillins?

Answer 11

Are inactivated or sensitive to the enzyme Beta-lactamase, which opens the beta-lactam ring making the antibiotic useless

Question 12

What is the clinical use for natural penicillins?

Answer 12

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

Question 13

Does class concept apply to natural penicillins?

Answer 13

Yes, test results from one antibiotic apply to all antibiotics of that class

Question 14

What are the semisynthetic beta-lactamase resistant penicillins?

Answer 14

Oxacillin
Methicillin
Cloxacillin

Mainly used to treat staphylococcal infections, have a narrow gram positive spectrum
Cloxacillin commonly used, more stable, class concept applies

Question 15

What is the bacterial resistance to semisynthetic penicillins?

Answer 15

Is due to altered penicillin binding proteins in their cell walls that prevent the antibiotic from binding

Question 16

What are the aminopenicillins?

Answer 16

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

Question 17

What are anti-pseudomonal penicillins?

Answer 17

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

Question 18

What are the two groups of anti-pseudomonal penicillins?

Answer 18

Carboxy penicillins
- carbenicillin

Ureidopenicillins
- mezlocillin, azlocillin

Question 19

What are the two agents used, that when given in combination with beta-lactam antibiotics, the beta-lactamase enzyme is inhibited?

Answer 19

Clavulanic acid eg. Amoxicillin-clav, Ticarcillin-clav

Sulbactam

Question 20

What are cephalosporins?

Answer 20

A beta-lactam antibiotic
First produced from a fungus
Broad spectrum

Question 21

What is the first generation of cephalosporins?

Answer 21

Include cephlaothin, cefazolin, cephalexin

More expensive
Class concept generally applies
Injected, but cephalexin can be taken orally

Question 22

What is the second generation of cephalosporins?

Answer 22

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

Question 23

What is the third generation of cephalosporins?

Answer 23

Include cefixime, cefotaxime, ceftizoxime, cefoperazone, cefazidime, ceftriaxone

Broad spectrum, less against gram positives but more against enterobacteriaceae and pseudomonas
Class concept does not apply

Question 24

What is the fourth generation of cephalosporins?

Answer 24

Includes cefipime, cefipriome

Broad spectrum
Selection for antimicrobial susceptibility testing varies

Question 25

What is Aztreonam?

Answer 25

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

Question 26

What is imipenem?

Answer 26

``` Belongs to a class called carbapenems Bactericidal - binds to proteins of the cell wall causing bacterial cells to elongate and lyse Broad spectrum ```

Question 27

What is Vancomycin?

Answer 27

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

Question 28

What are the four groups of antibiotics that inhibit bacterial protein synthesis?

Answer 28

Macrolide Chloramphenicol Tetracyclines Aminoglycosides

Question 29

What is erythromycin?

Answer 29

Belongs to the group macrolides Binds to ribosomal sub units Usually bacteriostatic Narrow mainly gram positive spectrum, some gram negatives

Question 30

What is clindamycin?

Answer 30

Similar to Erythromycin Better absorption and penetration properties Better for treating anaerobic infections Associated side effect of diarrhea

Question 31

What is Chloramphenicol?

Answer 31

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

Question 32

What are Tetracyclines?

Answer 32

``` 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 ```

Question 33

What are Aminoglycosides?

Answer 33

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

Question 34

What are some Aminoglycosides currently in use?

Answer 34

``` Kanamycin Gentamicin Tobramycin Amikacin Netilmicin Spectinomycin Class concept does not apply ```

Question 35

What are some antimicrobials that inhibit DNA and RNA synthesis?

Answer 35

Fluoroquinolones Nalidixic Acid Metronidazole (Flagyl)

Question 36

What are Floroquinolones?

Answer 36

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

Question 37

What is Nalidixic Acid?

Answer 37

Belong to the class Quinolone Broad spectrum Treats urinary tract infections

Question 38

What is Metronidazole?

Answer 38

Effective against anaerobic infections Breaks up DNA strands - bactericidal Treats protozoan parasitic infections

Question 39

What are Polymyxins?

Answer 39

``` 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

Question 40

What are some antimicrobial agents that inhibit other metabolic cell processes?

Answer 40

Sulfonamides Trimethoptim Nitrofurantoin

Question 41

What are Sulfonamides?

Answer 41

``` 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 ```

Question 42

What is Trimethoprim?

Answer 42

Interferes with folic acid, using competitive inhibition Broad spectrum Often used with sulfonamide and the combination is called cotrimoxazole Used for urinary tract infections

Question 43

What is Nitrofurantoin?

Answer 43

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