9.2 Antibiotics

Question 1

Compare Bactericidal vs Bactericidal

Answer 1

Bactericidal: kill target organisms.

Bactericidal: inhibit/delay bacterial growth and replication.

Question 2

Give an example of a Quinolones and what does this inhibit?

Answer 2

Ciprofloxacin ➞ targets DNA girase which interferes with separation/reannealing of dsDNA ➞ Inhibits nucleic acid synthesis

Question 3

What is Trimethoprim?

Give an other drug with the same MoA

Answer 3

Folic acid antagonists ➞ blocks nucleotide synthesis

Sulphonamides (but rarely used)

Question 4

What is Rifampicin

Answer 4

Inhibits nucleic acid synthesis ➞ binds β-subunit of bacterial RNA polymerase

Question 5

Give an example of an aminoglycoside and what does this inhibit?

Answer 5

Gentamicin ➞ binds the 30s ribosomal subunit causing misreading of mRNA thus inhibiting protein synthesis

Question 6

Give an example of a Macrolide and what does this inhibit?

Answer 6

Erythromycin ➞ binds to the 50s ribosomal subunit, prevents movement of ribosome along mRNA, inhibiting translocation ➞ inhibits Protein Synthesis

Question 7

What do tetracylines inhibit?

Answer 7

binds to the 30s ribosomal subunit, preventing attachment of tRNA to ribosome complex, preventing additon of amino acids ➞ inhibiting protein synthesis

Question 8

Give 4 drugs that target cell wall synthesis and specifically explain how

Answer 8

1) Penicillin – binds and blocks peptidases involved in cross-linking the glycan molecules
2) Cephalosporins – same as penicillin
3) Vancomycin – hinders peptidoglycan elongation
4) Cycloserine – inhibits the formation of the basic peptidoglycan subunits

Question 9

What is the disk diffusion test + what would the results indicate

Answer 9

Measures antibacterial activity- effectivness of antibacterial

Confluent growth of bacteria “bacterial lawn” will be seen where growth is NOT inhibited

“Zones of inhibition” (no growth) will be seen when strain is susceptible to that antibiotic concentration in agar

Question 10

What is the E-test, how is it done and what can it help us determine?

Answer 10

Another way to determine antimicrobial sensitivity

Place a strip with antimicrobials onto agar plate ➞ strain of bacterium will not grow near a conc of antibioticif it is sensitive

Results can be used to determine a “Minimum inhibitory concentration (MIC)”.

Question 11

Define Minimum Inhibitory Concentration

Answer 11

Minimum concentration of antibiotic required to inhibit growth of a bacterium in vitro

Question 12

Define what is meant by “Breakpoint” and its relationship to MIC

Answer 12

A breakpoint is a chosen concentration of an antibiotic which defines whether a species of bacteria is susceptible or resistant to the antibiotic

If MIC is less than or equal to the susceptibility breakpoint the bacteria is considered susceptible to the antibiotic

Question 13

What are the 2 types of killing by antimicrobials, pharmacokinetically speaking

Compare these with drug examples

Answer 13

1) Time dependent killing

• requires prolonged antibiotic presence at site of infection but NOT high concentration
• pencillins, cephalosporins, glycopeptides

2) Concentration dependent killing

• requires high antibiotic concentration at site of infection but not for long
• aminoglycosides, quinolones

Question 14

Give some common antibiotics associated with the following side effects

1. Hypersensitivity
2. Liver problems
3. Ototoxicity
4. Ototoxicity

Answer 14

Hypersensitivity ➞ penicillans and cephalosporins

Liver problems ➞ penicillans and cephalosporins

Ototoxicity ➞ amino-glyocsides

OtotoxicityOtotoxicity➞ tetracyclines and macrolides

Question 15

Give 2 purposes of therapeutic drug monitoring

Answer 15

To ensure adequate dose and non-toxic dose

Question 16

Give 3 antibiotics which require therapeutic drug monitoring

Answer 16

Aminoglycosides, glycopeptides, vancomycin

Question 17

What 3 things can be used to monitor potential toxicity of aminoglycosides?

Answer 17

renal function, auditory function and stool chart

Question 18

What 3 things can be used to monitor potential toxicity of daptomycin?

Answer 18

creatine kinase, eosinophils and stool chart

Question 19

What can we use to monitor potential toxicity of chloramphenicol?

Answer 19

FBC

Question 20

Give 4 antibacterial-drug interactions

Answer 20

1. Penicillans and anti-coagulants
2. Sulphonureas and chloramphenicol
3. Bisphosphonates and amino-glyocsides
4. Cylosporin and macrolides

Question 21

What are the 3 classes of antimicrobial resistance and define each

Answer 21

Question 22

What is antimicrobial stewardship?

Answer 22

Healthcare system wide approach to promoting and monitoring appropriate use of antimicrobial drugs to preserve their future effectiveness.

Question 23

List 4 principles of antimicrobial stewardship (DR DO)

Answer 23

1) Don’t start antibiotics without clinical evidence of a bacterial infection
2) Review clinical diagnosis and need for antibiotics within 48 hours from first dose and make a clear plan of action
3) Document on medical chart and in patients medical notes the clinical indication, duration or review date, route and dose
4) Obtain cultures to go from broad to narrow spectrum

Question 24

Give 4 factors we must consider when choosing an antibiotic (SOSO)

Answer 24

1. site of infection
2. organisms involved
3. severity of infection and/or risk of rapid progression
4. spectrum of different antibiotics
5. organ dysfunction- renal, hepatic
6. allergies

Question 25

Give 3 current hospital superbugs

Answer 25

1) MRSA
2) Clostridium difficile
3) Multi-resistant gram-negatives eg. Multi-resistant Pseudomonas

Question 26

Give 3 current community superbugs

Answer 26

1) CA-MRSA
2) ESBL gram negatives
3) PVL staphloccus aures