Antibiotics

Question 1

Antibiotic action is achieved by: (3)

Answer 1

• Utilizing a target unique to bacteria (e.g. cell wall)
• Selectively targeting bacterial specific components (enzymes, ribosomes)
• Preventing transport of the drug into human cells (e.g. Metronidazole can only be transported into anaerobic bacteria).

Question 2

Antibiotics: Mechanism of action (3)

Answer 2

• Cell wall synthesis
• Nucleic acid synthesis
• Protein synthesis

Question 3

Antibiotic resistance can be:

• Intrinsic
• Acquired

Answer 3

Intrinsic resistance: due to inherent structural or functional characteristics

Acquired: bacteria have been evolving to resist antibacterial agents for billions of years through mutation and/or the transfer of resistance properties. This evolutionary phenomenon is accelerated by selection pressure from antibiotic use (including agriculture, aquaculture and horticulture) which provides a competitive advantage for mutated, resistant strains.

Question 4

Guide to antibiotic prescribing:

• Start smart
• Then focus

Answer 4

Start smart:

1. Do not prescribe antibiotics in the absence of clinical evidence of bacterial infection, or for a self-limiting condition.
2. Take microbiological samples before prescribing.
3. Follow local guidelines first
4. Consider benefit and harm for each individual patient (allergies - clarify reaction, dose adjust for renal function + weight, medication interactions, pregnancy + lactation)
5. Prescribe the shortest effective course.

Then focus: Review the clinical diagnosis and continuing need for antibiotics at 48 hrs for all in-patients and all patients prescribed IV antibiotics.

Question 5

Antimicrobial stewardship: Definition

Answer 5

Antimicrobial stewardship is the systematic effort to educate and persuade prescribers of antimicrobials to follow evidence-based prescribing, in order to stem antibiotic overuse, and thus antimicrobial resistance

Question 6

Local resistance and guidelines

Answer 6

The bacteria in different populations develop resistance to different antibiotics. For example the e. coli in one area of the country might be particularly resistant to trimethoprim whereas in another area of the country they may be resistant to nitrofurantoin but sensitive to trimethoprim. Therefore it is necessary to have local policies that guide what antibiotics to use in different scenarios.

TOP TIP: In your OSCEs questions about treating infections can always be answered with “treat with antibiotics as per the local antibiotic policy”.

Question 7

Mechanism of action: Antibiotics That Inhibit Cell Wall Synthesis

Answer 7

ABx with Beta-lactams ring:
(beta-lactam cell wall inhibitors)
- Pencillins
- Cephalosporins
- Carbapenems

ABx without Beta-lactam ring:
(Non-beta-lactam cell wall inhibitors)
Glycopeptides:
- Vancomycin
- Teicoplanin

Polymyxins
- Colistin

Question 8

Mechanism of action: Antibiotics that inhibit protein synthesis by targeting the ribosome

Answer 8

50S subunit:

• Macrolides
• Clindamycin
• Linezolid
• Chloramphenicol
• Fusidic acid

30S

• Aminoglycosides
• Tetracyclines

Question 9

Mechanism of action: Antibiotics that inhibit Nucleic acid synthesis

Answer 9

Folate synthesis:

• Sulfamethoxazole
• Trimethoprim

DNA synthesis:

• Fluoroquinolones
• Metronidazole

RNA polymerase:
- Rifammycins

Question 10

Pencillin allergy: Overview

Answer 10

“Penicillin allergy” is very common. True penicillin allergy can lead to anaphylaxis and death so should not be taken lightly. The problem is that true allergy is much more rare than reported allergy and being labelled as penicillin allergic stops patients from getting many potentially life saving antibiotics.

Around 10% of patients report penicillin allergy however only around 10% of patients that report penicillin allergy have a true allergy to penicillin.

It is often believed that 10% of patients with penicillin allergy will have a reaction to cephalosporins and carbapenems. In reality this is closer to 1%.

TOP TIP: When taking an allergy history always ask what reaction patients have had to become labelled allergic. If they report diarrhoea for example, this is a side effect rather than an allergy and means if necessary (for example in life threatening sepsis) they can still receive that medication.