The document discusses different classes of beta-lactam antibiotics including penicillins, cephalosporins, carbapenems, monobactams, and their coverage of various bacteria. It notes that all beta-lactams contain a beta-lactam ring but differ in their side chains. Resistance can occur via changes to penicillin binding proteins or beta-lactamase production. Certain antibiotics like cefepime, carbapenems, and piperacillin-tazobactam provide coverage against both Pseudomonas and methicillin-sensitive Staphylococcus aureus.

1. Parker Power Hour on Beta-Lactam Antibiotics
The bacterial cell wall is made up of repeating molecules which are linked by PBP (penicillin binding
protein).
Every beta-lactam has the same beta-lactam ring. The difference between all antibiotics in this group are
the side chains of the antibiotics.
There are 2 methods of microbial resistance for beta-lactams –
- Change the penicillin binding protein (MRSA)
- Creation of a beta-lactamase enzyme
There are four classes of beta-lactams:
Penicillins
Natural – penicillin-G/VK
- Syphilis – genome does not exchange DNA with others very well, so no resistance acquired
- Group A Strep – not much resistance
Aminopenicillins – ampicillin (PO/IV), amoxicillin (PO/IV)
- More Gram negative coverage compared to natural penicillins
- Ear/sinus infections
- Listeria (meningitis in age > 50) – ampicillin
- Enterococcus (if sensitive)
- Group A Strep (amoxicillin can be added for improved coverage when D/C home for
cellulitis)
Anti-Staph – nafcillin
- MSSA bacteremia
Combination – amoxicillin-clavulanate, ampicillin-sulbactam, piperacillin-tazobactam
- Piperacillin-tazobactam has Psuedomonas coverage and more Gram negative/anaerobic
coverage compared to ampicillin-sulbactam
- Good coverage of MSSA, anaerobes
- No MRSA coverage
Penicillin allergy – only 10% with a non-anaphylaxis allergy to penicillins will react to skin testing for
penicillins. 99% will tolerate carbapenems.

2. Cephalosporins
Can not treat Listeria, Enterococcus, most anaerobes
1st
generation – cefazolin (IV), cefalexin (PO)
- Good coverage against MSSA (including bacteremia), non-purulent cellulitis w/o MRSA risks
o Nafcillin has some evidence that it is better for severe MSSA infections
2nd
generation – skip, we don’t use them much in the hospital
3rd
generation – ceftriaxone, ceftazadime, cefpodoxime, cefotaxime
- Ceftriaxone – MSSA coverage + more Gram negatives (Klebsiella, abdominal infections)
- Ceftazadime – Pseudomonal coverage, less Gram positive coverage
4th
generation – cefepime
- Love child of ceftriaxone and ceftazadime – good Psuedomonal and Gram positive coverage
5th
generation – ceftaroline
- MRSA coverage. Coverage is otherwise similar to ceftriaxone (no anaerobes or
Pseudomonas)
- Approved for skin/soft tissue and community acquired pneumonia (FOCUS1/2 Trials)
-
Combination cephalosporins – combined with a beta-lactamase
- Ceftazidime/avibactam – ESBL (inhibits all beta-lactams except carbapenems),
Pseudomonas.
- Ceftolozane/tazobactam – ESBL (inhibits all beta-lactams except carbapenems),
Pseudomonas. Poor anaerobic coverage.
Carbapenems
Great activity against Gram positive/negative, anaerobes, and covers Enterococcus faecalis (not
faecium) and Pseudomonas (with 1 exception)
- Imipenem-cilastin (inhibits renal enzyme that breaks down imipenem) – cover Enterococcus
and Pseudomonas
- Meropenem– cover Enterococcus and Pseudomonas
- Ertapenem – misses E. faecalis and Pseudomonas but has once daily dosing
- Doripenem – has best Pseudomonal coverage but not used at VM
Combination
- Meropenem-vaborbactam – for CRE or KPC organisms – LAST LINE antibiotic

3. Monobactams
Aztreonam – treats Gram negative aerobes including Pseudomonas (though not great based on our
antibiogram at VM). Side chain is very different so people who have reactions to other beta-lactams
(except ceftazidime) can often tolerate aztreonam.
Pseudomonas Coverage:
Piperacillin-tazobactam
Ceftazadime
Cefepime
Ceftazidime/avibactam
Ceftolozane/tazobactam
MRSA Coverage:
Ceftaroline
5 beta-lactams that cover Pseudomonas + MSSA
Cefepime
Imipenem
Meropenem
Doripenem
Piperacillin-tazobactam