Antimicrobial agents

Question 1

Inhibit of cell wall synthesis

Answer 1

Penicillin, cephalosporins, imipenem, meropenem, aztreonam, vancomycin

Question 2

Inhibit of bacterial protein synthesis

Answer 2

Aminoglycosides, chloramphenicol, macrolides, tetracyclins, streptogramins, linezolid

Question 3

Inhibit of nucleic synthesis

Answer 3

Flouroquinolones, rifampin

Question 4

Inhibit of folic acid synthesis

Answer 4

Sulfonamides, trimethoprim, pyrinethamine

Question 5

Penicillins

Answer 5

Mechanism of action:
Bacterial cell wall is cross-linked polymer of polysaccharides and pentapeptides
Penicillins interact with cytoplasmic membrane-bingding proteins (PBPS) to inhibit transpeptidation reaction involved in cross-linking, the final steps in cell-wall synthesis
Mechanism of resistance:
Penicillinases (Beta lactamases) break lactam ring structure (staph)
Structural change in PBPs (MRSA)
Change in porin structure (Pseudomonas)

Question 6

Narrow spectrum, beta lactamase sensitive (P)

Answer 6

Penicillin G, V

Spectrum: Strep, pneumococci, menigococci, Treponema pallidum, Syphillis

Question 7

Very narrow spectrum, beta lactamase resistant (P)

Answer 7

Methicillin, nafcillin, oxacillin

Spectrum: Staph (not MRSA)

Question 8

Broad spectrum, beta lactamase sensitive (P)

Answer 8

Ampicillin, amoxicillin
Spectrum: Gram + cocci (not staph), Ecoli, H Influenza, Listeria Mono (ampi) Borrelia burgdorferi (amox), H.pylori (amox)

Question 9

Extended spectrum, beta lactamase sentitive (P)

Answer 9

Antipseudomonal

Ticarcillin, piperacillin, azlocillin, carbenicillin

Question 10

Pharmacokinetics of Penicillins

Answer 10

Most are eliminated via active tubular secretion so can be toxic to kidney
Nafcillin and oxacillin eliminated largely in bile so in case of liver failure->dose adjustment is needed

Question 11

Side effects of Penicillins

Answer 11

Hypersensitivity (skin rash, anaphylaxis reaction…)
GI distress (normal flora is destroyed, especially ampicillin)
Jarisch-Herxheimer reaction in treatment of syphillis

Question 12

Cepha 1st genetation

Answer 12

cefazolin, cephalexin
Spect: gram+ cocci (not MRSA), E.coli, Klebsiella pneumoniae, and some Proteus
Use in Surgical prophylaxis
non enter CNS

Question 13

Cepha 2nd generation

Answer 13

cefuroxime, cefotetan, cefactor
Spect: some more gram - (anaerobes)
Cefuroxime can cross BBB!!!

Question 14

Cepha 3rd generation

Answer 14

ceftriaxone (IM) , cefotaxime (parenteral), cefixime (oral)
Spect: gram+, gram - cocci, and many gram - rods!!!
can cross BBB so very important in Emperic management of meningitis and sepsis

Question 15

Cepha 4th generation

Answer 15

cefepime (IV)
even wider spectrum
beta lactamase resistant!!!
enter CNS

Question 16

Imipenem and Meropenem

Answer 16

Mechanism same as penicillins and cephalosporins
Resistant to beta lactamases!!!
Spect: very broad
important in hospital for empiric use in severe life threatening infections
Pharmacokinetics: Imipenem is given with CILASTATIN, which inhibit imipenem’s metabolism to a nephrotoxic metabolite!!
Decrease dose in renal failure
Side effects: GI distress, drug fever

Question 17

Aztreonam

Answer 17

Mechanism of action: same as penicillins and cephalosporins
Resistant to beta-lactamases
Use: IV drug mainly active versus gram-negative rods
No cross allergenicity with penicillins or cephalosporins

Question 18

Vancomycin

Answer 18

Binding at the D-ala-D-ala muramyl pentapeptide to sterically hinder the transgly-cosylation reactions involved in elengation of peptidoglycan chains
Does not interfere with PBPs
Spect: MRSA, Entercocci, Clostridium difficile (backup drug)
Resistance:
VRSA and VRE strains emerging
Side effects: Red man syndrome, nephrotoxicity