S9) Antimicrobial Agents

Question 1

What is an antibacterial drug?

Answer 1

An antibacterial drug is a chemical substance that kills or inhibits the growth of bacteria at a discrete target site

Question 2

What is an antibiotic?

Answer 2

An antibiotic is an antibacterial drug of microbial origin e.g. penicillin from Penicillium mold

Question 3

What is the unique property of antimicrobials?

Answer 3

Antimicrobials target microbial biochemistry

Question 4

Identify some antibiotics which target DNA synthesis

Answer 4

• Quinolones e.g. ciprofloxacin
• Folic acid antagonists e.g. trimethoprim sulphonamides

Question 5

Identify some antibiotics which target protein synthesis

Answer 5

• Aminoglycosides e.g. gentamicin
• Macrolides e.g. erythromicin
• Tetracyclines

Question 6

Identify some antibiotics which target cell wall synthesis

Answer 6

• Beta-lactams e.g. penicillins, cephalosporins, carbapenems
• Glycopeptides e.g. vancomycin

Question 7

What are the two reasons for antibiotics?

Answer 7

• Prevention of infections
• Therapy of significant bacterial infections

Question 8

Identify some groups of people at increased risk of infection

Answer 8

• Peri-operative – prevention of surgical site infections
• Short term – meningitis contacts
• Long term – asplenia, immunodeficiency

Question 9

What are clinically significant infections?

Answer 9

Clinically significant infections are infections that if left untreated will cause death, permanent harm or medium to long term disability

Question 10

What are the two ways in which one can treat a clinically significant infection?

Answer 10

• Treatment of culture-proven infection
• Empirical treatment of suspected infection

Question 11

What are the two different ways that one might use antibiotics empirically?

Answer 11

Question 12

Which factors helps one determine the likely cause of an infection?

Answer 12

Question 13

Which factors helps one determine which antibiotics are likely to be effective?

Answer 13

Question 14

Which factors helps one determine which antibiotic is the best choice?

Answer 14

Question 15

What are the adverse events of antibiotics?

Answer 15

• Toxicities
• Allergic reactions
• Idiosyncratic reactions
• Ecological effects – C.difficile, selection of resistance
• Drug interactions

Question 16

What would ideal antibiotic therapy look like?

Answer 16

• Clean kill of infecting bacteria – minimal impact on commensal organisms, no resistance in any surviving pathogens
• No unwanted effects in patient e.g. drug interactions, toxicities

Question 17

Illustrate how one measures the susceptibility of bacteria to antibacterials

Answer 17

Question 18

What is the minimum inhibitory concentration?

Answer 18

MIC is the minimum concentration of antibiotic required to inhibit growth of a bacterium in vitro (mg/l)

Question 19

Therapeutic drug monitoring is used to ensure a non-toxic adequate dose for some antibiotics.

Identify these

Answer 19

• Aminoglycosides
• Glycopeptides

Question 20

Describe the mechanism of antibiotic resistance through the following pathways:

• Antibiotic inactivation
• Alteration of target site
• Alteration of metabolic pathways
• Reduced intracellular antibiotic accumulation

Answer 20

Question 21

What does it mean when a pathogen is multi-drug resistant?

Answer 21

Multi-drug resistant – non-susceptibility to at least one agent in three or more antimicrobial categories

Question 22

What does it mean when a pathogen is extensively drug resistant?

Answer 22

Extensively drug resistant – on-susceptibility to at least one agent in all but two or fewer antimicrobial categories

Question 23

What does it mean when a pathogen is pan drug resistant?

Answer 23

Pan drug resistant – non-susceptibility to all agents in al antimicrobial categories

Question 24

Identify the two ways in which bacteria can become resistant to carbapenem

Answer 24

• Reduced bacterial intracellular concentration
• Carbapenemase production