9. Antimicrobial Agents

Question 1

What is the unique property of antimicrobials?

Answer 1

They ideally have no direct effect on the patient.

Question 2

What are the three main targets of antibiotics?

Answer 2

DNA synthesis, protein synthesis, cell wall synthesis.

Question 3

Which groups of antibiotics target DNA synthesis? Give an example of each.

Answer 3

Quinolones - ciprofloxacin. Folic acid antagonists - trimethoprim, sulphonamides.

Question 4

Which groups of antibiotics target protein synthesis? Give an example of each.

Answer 4

Aminoglycosides - gentamicin. Macrolides - erythromicin. Tetracyclines - tetracycline.

Question 5

Which groups of antibiotics target cell wall synthesis? Give an example of each.

Answer 5

Beta-lactams - penicillins, cephalosporins, carbapenems. Glycopeptides - vancomycin.

Question 6

What are the two good reasons for using antibiotics?

Answer 6

Prevention of infections, and therapy of significant bacterial infections.

Question 7

Which three groups of people should be given antibiotic prophylaxis?

Answer 7

Perioperative, short term (e.g. meningitis contacts), long term (e.g. aplenia, immunodeficiency).

Question 8

What should the approach to antimicrobial treatment of significant bacterial infections be?

Answer 8

Treat culture proven infection but treat empirically if suspected infection.

Question 9

What should be considered in empiric use of antibiotics?

Answer 9

What the likely cause of infection is, which antibiotics are likely to be effective, which effective antibiotic is the best choice.

Question 10

Why must empiric treatment be considered in acutely ill patients?

Answer 10

Culture results can take 24-72 hours to get back and in that time, the patient may have seriously deteriorated.

Question 11

What factors should be considered when trying to identify the likely cause of an infection?

Answer 11

Duration of illness, past medical history, occupational history, travel history, time of year, age, personal background, anatomical site.

Question 12

What should be considered when trying to identify which antibiotics are likely to be considered?

Answer 12

Likely susceptibility and consequence of wrong choice - severity of infection, immune status of patient, baseline rate of resistance, community or healthcare onset.

Question 13

What should be considered when trying to decide which effective antibiotic should be used?

Answer 13

Cost, efficacy, administration route, safety - age/toxicity/drug interaction/allergies/pregnancy/breast feeding/organ function.

Question 14

What are the two outcomes of an ideal antibiotic therapy?

Answer 14

No effect on patient but clean kill of infecting bacteria (no resistance and minimal impact on non-target commensal organisms).

Question 15

What are the ADRs of antibiotics?

Answer 15

Pharmacological - toxicities, drug interactions; allergic reaction; impact on normal flora.

Question 16

What is therapeutic drug monitoring used to ensure?

Answer 16

Adequate dose and non-toxic dose.

Question 17

Which antibiotic class is drug monitoring used for?

Answer 17

Aminoglycosides.

Question 18

How can antibiotic sensitivity be measured?

Answer 18

Disc sensitivity.

Question 19

What are the types of genetic basis of antibiotic resistance?

Answer 19

Chromosomal gene mutation, and horizontal gene transfer.

Question 20

Explain chromosomal gene mutation.

Answer 20

Mutated gene conferring resistance is selected with antibiotic use as the non-mutated types are cleared and it proliferates.

Question 21

Explain horizontal gene transfer.

Answer 21

Plasmids with gene for resistance are spread between bacteria.

Question 22

What are the four main forms of antibiotic resistance?

Answer 22

Antibiotic inactivation, alteration of target site, alteration of metabolic pathways, reduced intracellular antibiotic accumulation.

Question 23

Give an example of resistance by antibiotic inactivation.

Answer 23

Beta-lactamase.

Question 24

Give an example of resistance by altered target site.

Answer 24

Penicillin binding protein.

Question 25

Give an example of resistance by altered metabolic pathways.

Answer 25

Folic acid used instead of para-aminobenzoic acid.

Question 26

Give an example of resistance by reduced intracellular antibiotic accumulation.

Answer 26

Active efflux mechanisms or decreased permeability.

Question 27

How can antibiotic resistance be prevented?

Answer 27

Antimicrobial stewardship and infection control.

Question 28

What are the rules of antimicrobial stewardship?

Answer 28

Right antibiotic at the right time at the right dose, frequency, and duration via the right route.

Question 29

What is meant by time dependent or concentration dependent killing in successful treatment using antimicrobials?

Answer 29

Time - successful treatment needs prolonged antibiotic presence at site of infection but not at high concentrations.
Concentrations - successful treatment requires high antibiotic concentration at site of infection but not for a long time.

Question 30

How can infection control decrease antibiotic resistance?

Answer 30

Prevent exposure to antibiotics - minimise risk of infection, monitor and control antibiotic prescribing. Prevent spread of resistant bacteria - isolation or cohorting, hand hygiene, decolonisation of patients.