Antibiotics

Question 1

Vancomycin

Answer 1

1. Action: during cell-wall synthesis it binds to D-alanyl-D-alanine and inhibits PG cross-linking
2. Activity: cidal
3. Spectrum: narrow
   Mostly G+ cocci and bacilli (esp. penicilinase-resistant S. aureus)
4. Pregnancy safe
5. Treatment of choice for MRSA

Question 2

Penicillins

Answer 2

1. Action: during last stage of cell wall synthesis it blocks transpeptidase and inhibits PG cross-linking
2. Activity: cidal
3. Spectrum: narrow->broader
4. Pregnancy safe
5. B-lactam rings cleaved by bacteria with B-lactamase (penicillinase). 10% risk of hypersensitivity.

Question 3

Cephalosporins

Answer 3

1. Action: transpeptidase block
2. Activity: Vidal
3. Spectrum: narrow->broader
4. Pregnancy safe
5. B-lactam rings, 10% cross-hypersensitivity with penicillins

Question 4

Metronidazole

Answer 4

1. Action: inhibits DNA synthesis
2. Activity: cidal
3. Spectrum: narrow (anaerobes and some protozoa)
4. NOT pregnancy safe
5. Pseudomembranous colitis, disulfiram-like reaction with alcohol

Question 5

Fluoroquinolones

Answer 5

1. Action: inhibit DNA gyrase (topoisomerase)
2. Activity: cidal
3. Spectrum: broader (G+, G-, Mycobacteria, NOT anaerobes)
4. NOT pregnancy safe
5. Disulfiram-like reaction with alcohol
6. Ex: Ciprofloxacin, Ofloxacin

Question 6

Aminoglycosides

Answer 6

1. Action: binds 30S -> block formation of initiation complex -> inhibit protein synthesis
2. Activity: cidal, G+ and G- aerobes ONLY
3. Spectrum: broader
4. NOT pregnancy safe
5. Ototoxicity, nephrotoxicity, teratogens
6. Ex.: Streptomycin, Gentamycin

Question 7

Macrolides

Answer 7

1. Action: binds 50S -> block tRNA release -> inhibit protein synthesis
2. Activity: static
3. Spectrum: narrow
4. Pregnancy safe
5. GI upset
6. Ex.: Erythromycin, Clarithromycin, Azithromycin

Question 8

Clindamycin

Answer 8

1. Action: binds 50S -> block tRNA release -> inhibit protein synthesis
2. Activity: static
3. Spectrum: narrow
4. Pregnancy safe
5. Ass. with diarrhea and pseudomembranous colitis (overgrowth of C. difficile)

Question 9

Chloramphenicol

Answer 9

1. Action: blocks 50S -> blocks peptidyl transferase -> inhibits protein synthesis
2. Activity: static
3. Spectrum: broad
4. NOT pregnancy safe
5. Bone marrow toxicity, gray baby syndrome

Question 10

Tetracyclines

Answer 10

1. Action: binds 30S -> block aminoacyl-tRNA binding -> inhibit protein synthesis
2. Activity: static
3. Spectrum: broad
4. NOT pregnancy safe
5. Divalent and trivalent cations inhibit absorption, staining teeth during calcification
6. Ex.: Tetracycline, Doxycycline, Minocycline

Question 11

Sulfonamides

Answer 11

1. Action: competes with PABA -> inhibits folic acid synthesis
2. Activity: static
3. Spectrum: broad
4. NOT pregnancy safe
5. Ass. with hypersensitivity, renal toxicity, hematopoietic toxicity
6. Ex.: Sulfadiazine, Sulfamethoxazole, Trimethoprim

Question 12

Neomycin

Answer 12

• topical

- aminoglycoside

Question 13

Polymyxin B

Answer 13

• topical

- alters cell membrane permeability

Question 14

Bacitracin

Answer 14

• topical

- inhibits cell wall synthesis