Antibiotics

Question 1

What are the unique properties of antimicrobials?

Answer 1

Antimicrobials target microbial biochemistry.

This means that the ideal antimicrobial would have no direct impact on patient biochemistry or physiology.

Question 2

How do antibiotics work?

Answer 2

Antibiotics work by sticking to specific bacterial molecules, interfering with their shape and consequently their function.

For example penicillin binds to DD-transpeptidase, a bacterial protein that is vital for making the outer cell wall of bacteria.
As a result of penicillin’s action, the cell wall is weakened and the bacteria burst.

Question 3

Give examples of antibiotics that target DNA synthesis

Answer 3

Quinolones - Ciprofloxacin

Folic acid antagonists - Trimethoprim, Sulphonamides

Question 4

Give examples of antibiotics that target protein synthesis

Answer 4

Aminoglycosides - gentamicin

Macrolides - erythromycin

Tetracyclines

Question 5

Give examples of antibiotics that target cell wall synthesis

Answer 5

Beta-lactams - penicillins, cephalosporins, carbapenems

Glycopeptides - Vancomycin

Question 6

What are the different sites of action of antibiotics?

Answer 6

Cell wall synthesis - beta-lactams, glycopeptides

Protein synthesis - Aminoglycosides, macrolides, tetracyclines

DNA synthesis - Quinolones, Folic acid antagonists

Question 7

What are the two reasons you can take antibiotics

Answer 7

Prophylaxis of bacterial infections for people at increased risk of infection

• e.g.Peri-operative (prevent surgical site infection)
• Short term - meningitis contacts
• Long term - Asplenia, immunodeficiency.

Therapy of significant bacterial infections.

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

Question 8

How do you use antibiotics empirically?

Answer 8

Follow the local antibiotic formulary

OR

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

Question 9

What do you have to taken into account to work out the likely cause of infection?

Answer 9

Anatomical site
Duration of illness
Past medical history 
Occupational history 
Travel history 
Time of year
Age
Personal Background

Question 10

What things do you need to know to work what antibiotics are likely to be best?

Answer 10

Community or healthcare onset?
Severity of infection?
Immune statins of patient
Baseline rate of resistance

• Likely susceptibility
• Consequences of wrong choice

Question 11

What do you take into account to work out what antibiotic is best?

Answer 11

Saftey: 
Drug interactions 
Allergies
Pregnancy, breast feeding 
Organ function 
Route administration 
Cost 
Efficacy
Age
Toxicity

Question 12

How do you measure antibiotic activity?

Answer 12

Disc testing - measure antibiotic activity by disc testing. -Measure zone of inhibition

Question 13

What is the MIC?

Answer 13

Minimum inhibitory concentrations

MIC measurements are for a specific organism and antibacterial combination.

Question 14

What is time dependant killing?

Answer 14

Successful treatment required prolonged antibiotic presence at site of infection/

But not high concentration

fT >MIC - fraction of time concentration of unbound drug is greater than MIC.

Question 15

What is concentration dependant killing?

Answer 15

Successful treatment required high antibiotic concentration at site of infection

But not for long

[Cmax]/MIC ratio of maximum unbound drug concentration to MIC

Question 16

Why is therapeutic drug monitoring used?

Answer 16

To ensure adequate but non toxic dosing of drugs.

Used for aminoglycosides and vancomycin.

Question 17

What is the difference between innate and acquired resistance?

Answer 17

Innate - bacteria has never been sensitive.

Acquired - more dangerous as previously sensitive but now resistance.

Question 18

How do bacteria become resistant to antibiotics?

Answer 18

Bacteria develop resistance to antibiotics in two main ways:

• Mutation of their DNA (haphazard changes in chromosomal or plasmid DNA
• Acquisition of pre-formed resistance genes (transfer through plasmids).