Chloramphenicol, Tetracyclines, Macrolides, Clindamycin & Linezolid

Question 1

What antibiotics bind to the 50s ribosomal subunit and block transpeptidation?

Answer 1

Chloramphenicol

Macrolides

Question 2

What class of antibiotics bind to the 30s subunit and block the incoming charged tRNA?

Answer 2

Tetracyclines

Question 3

What protein synthesis inhibitors are bactericidal?

Answer 3

Aminoglycosides
Linezolid (variable)

Question 4

What is the MOA of chloramphenicol?

Answer 4

Binds to 50s ribosomal subunit

Blocks transpeptidation

Question 5

What is the MOA of tetracyclines?

Answer 5

Binds to 30s ribosomal subunit

Blocks binding of charged tRNA

Question 6

What is the MOA of macrolides?

Answer 6

Binds to 50s ribosomal subunit

Blocks transpeptidation

Question 7

Chloramphenicol has limited use owing to toxicities but is often still used in developing countries because of the low cost. What toxicities are associated with chloramphenicol?

Answer 7

Anemia
Aplastic anemia
Gray baby syndrome

Question 8

How do bacteria gain resistance to chloramphenicol?

Answer 8

Plasmid

Encodes acetyltransferase that inactivates the drug

Question 9

What are the clinical uses of chloramphenicol?

Answer 9

Rocky Mountain spotted fever (Rickettsia rickettsii)

Question 10

Although chloramphenicol can be used to treat Rocky Mountain spotted fever, what is the preferred agent?

Answer 10

Doxycycline

Question 11

Is chloramphenicol bactericidal or bacteriostatic?

Answer 11

Bacteriostatic

Question 12

List the tetracyclines.

Answer 12

Tetracycline
Doxycycline
Minocycline

Question 13

What compounds inhibit tetracycline absorption in the gut?

Answer 13

Divalent cations

milk, antacids, iron

Question 14

How do bacteria gain resistance against tetracyclines?

Answer 14

Plasmid

Decreased uptake or increased efflux by transport pumps

Question 15

What is a contraindication for tetracycline use?

Answer 15

Pregnancy

Question 16

What toxicities are associated with tetracyclines?

Answer 16

GI distress
Photosensitivity
Discoloration of teeth and inhibition of bone growth in children

Question 17

What are indications to use tetracyclines?

Answer 17

Borrelia burgdorferi
M. pneumoniae
Ricketssia
Chlamydia
Acne

Question 18

Why are tetracyclines very effective against Ricketssia and Chlamydia?

Answer 18

Accumulate intracellularly

Question 19

List the macrolides.

Answer 19

Erythromycin
Azithromycin
Clarithromycin

Question 20

Are tetracyclines bactericidal or bacteriostatic?

Answer 20

Bacteriostatic

Question 21

Are macrolides bactericidal or bacteriostatic?

Answer 21

Bacteriostatic

Question 22

What are the clinical uses of macrolides?

Answer 22

Atypical pneumonias
B. pertussis
STIs (Chlamydia)
Gram positive cocci in patients allergic to penicillin

Question 23

What is the treatment for N. gonorrhea?

Answer 23

Ceftriaxone

Azithromycin to empirically treat for Chlamydia

Question 24

How do bacteria gain resistance against macrolides?

Answer 24

Methylation of 23s rRNA binding site inhibits binding of drug

Question 25

What effect do clarithromycin and erythromycin have on the CYP450 enzyme system?

Answer 25

Inhibitors

Question 26

What are the toxicities associated with macrolides?

Answer 26

``` M: motility issues (GI) A: arrhythmia (QT prolongation) C: cholestasis (acute cholestatic hepatitis) R: rash O: eOsinophilia ```

Question 27

What is the MOA of clindamycin?

Answer 27

Binds 50s ribosomal subunit | Blocks peptide transfer

Question 28

Is clindamycin bactericidal or bacteriostatic?

Answer 28

Bacteriostatic

Question 29

What are indications for clindamycin?

Answer 29

Treats anaerobic infections above the diaphragm | Group A strep

Question 30

What toxicities are associated with clindamycin?

Answer 30

Pseudomembranous colitis Fever Diarrhea

Question 31

What drug binds to the 50s ribosomal subunit and prevents formation of the initiation complex?

Answer 31

Linezolid

Question 32

When in linezolid used?

Answer 32

MRSA | VRE

Question 33

How do bacteria acquire resistance to linezolid?

Answer 33

Point mutation of ribosomal RNA

Question 34

What toxicities are associated with linezolid?

Answer 34

Bone marrow suppression (especially thrombocytopenia) Peripheral neuropathy Serotonin syndrome

Question 35

A bacteria aquires a methylase that adds a methyl group to the ribosomal binding site of azithromycin. What other drug, other than macrolides, will the bacteria be resistant to?

Answer 35

Clindamycin