Master the board step 3

Master the Boards: USMLE Step 3
If the organism is sensitive,
oxacillin and nafcillin are
superior to vancomycin.
Streptococcus
The medications above will cover Streptococcus as well as Staphylococcus.
The following medications are specific for Streptococcus:
··
Penicillin
··
Ampicillin
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Amoxicillin
Gram-negative bacilli (rods): Escherichia coli, Enterobacter,
Citrobacter, Morganella, Pseudomonas, Serratia
All of the following medications are essentially equal in their efficacy for gramnegative
bacilli.
Cephalosporins Penicillins Monobactam Quinolones Aminoglycosides Carbapenems
Cefepime
Piperacillin
Aztreonam
Ciprofloxacin
Gentamicin
Imipenem
Ceftazidime
Ticarcillin
Levofloxacin
Tobramycin
Meropenem
Moxifloxacin
Amikacin
Ertapenem
Gemifloxacin
Doripenem
Gemifloxacin is a quinolone
for pneumonia.
Exceptions
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Ertapenem is the only carbapenem that does not cover Pseudomonas.
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Piperacillin and ticarcillin also cover streptococci and anaerobes.
··
Levofloxacin, gemifloxacin, and moxifloxacin are excellent pneumococcal
drugs.
··
Aminoglycosides work synergistically with other agents to treat staph and
enterococcus.
··
Carbapenems are excellent antianaerobic medications. They cover streptococci
and all sensitive staphylococcus (MSSA).
··
Tigecycline covers MRSA and is broadly active against gram-negative
bacilli. Tigecyline is weaker than other anti-MRSA drugs.
Basic Science Correlate
Mechanism of Beta-Lactam Antibiotics
The 4 beta-lactam antibiotics all inhibit the cell wall by binding the
penicillin-binding protein. The 4 classes are:
••
Penicillin
••
Cephalosporins
••
Carbapenem
••
Monobactam (the only one is aztreonam)
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