Antibiotics

Question 1

What is the mechanism of trimethoprim?

Answer 1

Interferes with DNA synthesis by inhibiting dihydrofolate reductase

Question 2

What are the adverse effects of trimethoprim?

Answer 2

Myelosuppression
Transient rise in creatinine: trimethoprim competitively inhibits the tubular secretion of creatinine resulting in a temporary increase which reverses upon stopping the drug

Question 3

Why does trimethoprim increase creatinine?

Answer 3

locks the ENaC channel in the distal nephron, causing a hyperkalaemic distal RTA (type 4).
It also inhibits creatinine secretion, often leading to an increase in creatinine by around 40 points (but not necessarily causing AKI)

Question 4

What is the mechanism of doxycycline?

Answer 4

Bacterialstatic
- Protein synthesis inhibitor
- binds to 30S subunit blocking binding of aminoacyl-tRNA

Question 5

What is the resistant mechanism of doxycycline?

Answer 5

increased efflux of the bacteria by plasmid-encoded transport pumps, ribosomal protection

Question 6

What is the choice of antibiotic for UTI in pregnant women?

Answer 6

1. Nitrofuantoin (avoid in close to term)
2. Amoxicillin or cefalexin

Question 7

What antibiotic must be avoided in methotrexate?

Answer 7

Trimethoprim
Co-trimoxazole

Question 8

What is the mechanism of action of rifampicin?

Answer 8

Inhibits RNA synthesis
Bacteriostatic

Question 9

What antibiotics are bacterial static?

Answer 9

Bacteriostatic antibiotics
chloramphenicol
macrolides
tetracyclines
sulphonamides
trimethoprim

Question 10

What antibiotics are bactericidal?

Answer 10

Bactericidal antibiotics
penicillins
cephalosporins
aminoglycosides
nitrofurantoin
metronidazole
quinolones
rifampicin
isoniazid

Question 11

What antibiotics stop cell wall synthesis?

Answer 11

penicillins: binds transpeptidase blocking cross-linking of peptidoglycan cell walls
cephalosporins

Question 12

What antibiotics inhibit protein synthesis?

Answer 12

aminoglycosides (cause misreading of mRNA)
chloramphenicol
macrolides (e.g. erythromycin)
tetracyclines
fusidic acid

Question 13

What antibiotics stop DNA synthesis?

Answer 13

quinolones (e.g. ciprofloxacin)
metronidazole
sulphonamides
trimethoprim

Question 14

What antibiotics stop RNA synthesis?

Answer 14

Rifampicin

Question 15

What is red man syndrome and what causes it?

Answer 15

Vancomycin

Ototoxicity, nephrotoxicity and red man syndrome. Red man syndrome is associated with flushing or a maculopapular rash. The proposed mechanism is non IgE mediated mast cell degranulation. Red man syndrome is more common with higher flow rates of infusion. Treatment includes antihistamines.

Question 16

What is the coverage of linezolid?

Answer 16

Spectrum, highly active against Gram positive organisms including:
MRSA (Methicillin-resistant Staphylococcus aureus)
VRE (Vancomycin-resistant enterococcus)
GISA (Glycopeptide Intermediate Staphylococcus aureus)

Question 17

Adverse effects of linezolid?

Answer 17

Adverse effects
thrombocytopenia (reversible on stopping)
monoamine oxidase inhibitor: avoid tyramine containing foods

Question 18

Mechanism of action of linezolid?

Answer 18

Linezolid is a type of oxazolidinone antibiotic which has been introduced in recent years. It inhibits bacterial protein synthesis by stopping the formation of the 50s initiation complex and is bacteriostatic in nature.