▪️ Antimicrobials

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

The easy way
Follow the local
antibiotic formulary

The thoughtful way
What is the likely cause of infection?
Which antibiotics are likely to be
effective?
Which one is the best choice?

Question 12

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

Answer 12

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

Question 13

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

Answer 13

•Likely susceptibility
•Consequences of wrong choice
Is determined by:

Community or Healthcare onset?
Severity of infection
Baseline rate of resistance
Immune status of patient

Question 14

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

Answer 14

Safety is determined by :
Age, organ function, toxicity, drug interactions, allergies, pregnancy, breast-feeding, efficacy, cost, administration route

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

This is can be measured directly by bringing the pathogen and the antibiotic together in a growing environment, such as nutrient media in a test tube or agar plate, to observe the effect of the antibiotic on the growth of the bacteria.

Antibiotic susceptibility is determined by measuring the diameter of the zones of bacterial inhibition around the antibiotic disks and comparing the diameter with disk diffusion interpretive criteria updated annually by CLSI

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:

1. Antibiotic inactivation
2. Alteration of target site
3. Alteration of metabolic pathways
4. Reduced intracellular antibiotic accumulation

Answer 20

1. Beta lactamase
2. Penicillin binding protein
3. Para-aminobenzoic acid is normally required by bacteria but some can use preformed folic acid instead
4. Active efflux mechanisms + Decreased permeability

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