Antibiotics recap

Question 1

How do Beta Lactams work? Which categories of antibiotic are Beta Lactams? Give an example of each.

Answer 1

They inhibit cell wall synthesis by binding to Penicillin Binding Proteins

Penicillins (eg. Flucloxacillin, Amoxicillin)
- the obvious one

Cephalosporins (eg. Cefuroxime, Cefalexin)
- This makes me think about mushrooms for some reason

Carbapenems (eg. Meropenem)
- Panem means bread (from the Hunger Games lol) and carbs are in bread

Monobactams (eg. Aztreonam)
- If you smush beta lactam together you get bactam

Question 2

What kind of antibiotic is more susceptible to Beta Lactams? Why?

Answer 2

Gram positive organisms are more susceptible than gram negative

Gram negative organisms have an additional lipopolysaccharide layer that prevents antibiotic penetration

Question 3

Name 2 classes of antibiotic that inhibit cell wall synthesis. How are their mechanisms of action different? How do their spectrums differ? Why?

Answer 3

Beta lactams and glycopeptides

Beta lactams bind to Penicillin Binding Proteins (aka transpeptidases) which catalyse cross-links between adjacent glycan chains. Glycopeptides inhibit peptidoglycan synthesis

Beta lactams are more effective against gram positive than gram negative organisms (as the liposaccharide layer in gram negative organisms prevents antibiotic penetration)

Glycopeptides are completely ineffective against gram negative organisms (the molecule is too large to get through the porins in the outer membrane)

Question 4

List some differences between gram positive and gram negative organisms

Answer 4

Gram positive
- 1 cytoplasmic membrane
- Thicker peptidoglycan layer
- More susceptible to beta lactams

Gram negative
- 2 cytoplasmic membranes
- Additional lipoprotein layer
- Thinner peptidoglycan layer
- Less susceptible to beta lactams
- Not susceptible to glycopeptides

Question 5

How can you differentiate gram positive and gram negative organisms using staining?

Answer 5

Under a gram film:

Gram negative = Pink
Gram positive = Purple

Question 6

One of the beta lactams may need to be administered STAT in a primary care setting. Which one? Why?

Answer 6

Benzylpenicillin (aka penicillin G). Administer IM STAT if meningococcal septicaemia is suspected (as long as no history of anaphylactic reaction to penicillin - rash is not a contraindication) then refer to secondary care

Question 7

Name 2 glycopeptides and give a scenario when one may be used

Answer 7

Vancomycin. Treatment of C.difficile

Teicoplanin

Question 8

A patient who has recently been started on a new antibiotic has diarrhoea. What pathogen is suspected? Which antibiotics could be responsible? How do we treat (name and class)?

Answer 8

Clostridium difficile

The 4 Cs
- Clindamycin (think about an old lady named Linda)
- Co-amoxiclav (and some other penicillins)
- Cephalosporin (it’s the mushroom one again lol)
- Ciprofloxacin (aka fluoroquinolones aka anything ending in -floxacin, eg levofloxacin)

Treat with vancomycin (glycopeptide)

Question 9

Name 3 classes of antibiotic that inhibit nucleic acid synthesis

Answer 9

Fluoroquinolones (-floxacin)
Rifampicin
Metronidazole

Question 10

One antibiotic that inhibits nucleic acid synthesis is part of a multiple antibiotic regimen for a condition. Which one?

Additionally: Which condition? What’s the regimen? Side effects for each?

Answer 10

Rifampicin

Tuberculosis quadruple therapy (remember RIPE)

2 months
- Rifampin (haematuria)
- Isoniazid (peripheral neuropathy)

6 months
- Pyramidazole (hepatitis)
- Ethambutamol (eye problems)

Question 11

Protein synthesis inhibitors work by targeting a subunit of ribosomes. Which ones target which?

Answer 11

30S
- Tetracyclines (eg. Doxycycline)
- Aminoglycosides (eg. Gentamicin)

50S
- Lincosamides (eg. Clindamycin)
- Macrolides (eg. Clarithromycin)
- Chloramphenicol

Question 12

What is similar about clindamycin and clarithromycin? How are they different?

Answer 12

Similar
- Inhibit nucleic acid synthesis by targeting 50S subunit of ribosomes

Different
- CLINdamycin is a LINcosamide, clarithromycin is a macrolide
- Clindamycin is a cause of C.diff, clarithromycin is not (think about an old lady named LINDA)

Question 13

Name 3 classes of antibiotic that inhibit folate synthesis

Answer 13

Sulphonamides
Trimethoprim
Co-trimoxazole

Question 14

What is important to remember about folate synthesis antagonists?

Answer 14

They are TERATOGENIC

Definitely in the 1st trimester (first 12 weeks) but manufacturers recommend not giving to pregnant people at all

Remember - Folate is GOOD FOR BABIES (pregnant people take folic acid) so folate antagonists BAD