Beta Lactams Flashcards
Mechanism of Action
Inhibition of cell wall synthesis via inhibition of cross-linking of peptidoglyan in the cell wall, leading to autolysis and cell death. Bactericidal
Mechanism of Resistance
Beta-lactamase - acquired by plasmid transfer
Alteration of PBPs - due to mutation
PBPs
Penicillin binding proteins
MRSA resistance
Has acquired both Beta-lactamase and altered PBPs
PCN 1/2 life
<2 hours
PCN oral bioavailability
Poorly absorbed. This can lead to diarrhea.
PCN Hypersensitivity
If a pt has a true hypersensitivity rxn to PCN, other PCNs should be avoided, even if they are from different classes of PCNs. If the rxn is not severe, cephalosporins and carbapenems may be useful
Natural PCNs
PCN G (IV) PCN VK (PO) Procaine PCN (IM) Benzathine PCN (IM)
Natural PCN Spectrum: Good
Treponema pallidum (syphilis) Some streptococci
Natural PCN Spectrum: Moderate
Enterococci
Natural PCN Spectrum: Poor
Atypicals
Almost everything else (narrow spectrum of activity)
Antistaphylococcal PCN Spectrum: Good
MSSA
Streptococci
Antistaphylococcal PCN Spectrum: Poor
GNRs Enterococci Anaerobes Atypicals MRSA
Aminopenicillins Spectrum: Good
Streptococci
Enterococci
Aminopenicillins Spectrum: Moderate
Some GNRs
Aminopenicillins Spectrum: Poor
Staph
Anaerobes
Atypicals
Antistaphylococcal PCNs
Penicillinase-resistant
Nafcillin (IV)
Oxacillin (IV)
Dicloxacillin (PO)
Aminopenicillins
Extended-spectrum PCNs
Amoxicillin (PO)
Ampicillin (PO, IV)
Antipseudomonal PCNs
Broad-spectrum PCNs
Piperacillin (IV)
Ticarcillin (IV)
Antipseudomonal PCNs Spectrum: Good
Pseudomonas (And other GNRs)
Streptococci
Enterococci
Antipseudomonal PCNs Spectrum: Moderate
More resistant GNRs
Antipseudomonal PCNs Spectrum: Poor
Staph
Anaerobes
Atypicals
Beta-Lactam/Beta-Lactamase Inhibitor Combinations
Amoxicillin/Calvulanate
Ampicillin/sulbactam (Unasyn IV)
Pipercillin/tazobactam (Zosyn IV)
Ticarcillin/calvulanate (Timentin IV)
Beta-Lactam/Beta-Lactamase Inhibitor Combinations Spectrum: Good
MSSA Strep Enterococci Anaerobes Enteric GNRs (including pseudomonas w/only Zosyn & Timentin)
Beta-Lactam/Beta-Lactamase Inhibitor Combinations Spectrum: Poor
MRSA
Atypicals
ESBL producing Beta-lactamase
ESBL
Extended spectrum beta-lactamase
AE w/aminopenicillins
Similar to other beta-lactams
Diarrhea w/PO administration
More diarrhea with ampicillin than amoxicillin
AE w/antistaphylococcal PCNs
Similar to other beta-lactams
Interstitial nephritis, phlebitis
DOC for syphilis
Natural PCNs
Which PCN is eliminated via the liver
Antistaphylococcal PCNs
Which aminopenicillin has better oral absorption?
Amoxicillin
What is sulbactam good for?
Sulbactam has good activity against Acinetobacter
What is Acinetobacter?
A highly drug-resistant GNR that causes nosocomial infxns
Utility of natural PCNs
Syphilis
Susceptible strep infxn (pharyngitis, endocarditis)
Utility of antistaphylococcal PCNs
MSSA infxns (endocarditis, skin/soft tissue infxns)
Utility of aminopenicillins
Ampicillin DOC for susceptible enterococci
Susceptible GNRs
URTIs (pharyngitis, otitis media)
Utility of beta-lactam/beta-lactamase inhibitor combinations
Zosyn/Timentin: empiric therapy for nosocomial infxns
Augmentin: URTIs, LRTIs, UTIs
Mixed infxns d/t anaerobic activity (intraabdominal, diabetic ulcers, aspiration pneumonia)
How do aminopenicillins achieve bactericidal activity against enterococci?
Must be combined with an aminoglycoside
What are the options for staph?
Beta-lactams kill staph quicker than vancomycin. Patients with MSSA infxns who lack serious beta-lactam allergies should be switched to anti-staph PCN or 1st generation cephalosporin when possible
Cross-allergenicity of cephalosporins and PCNs
Reduced cross-allergenicity.
Most likely to cross with 1st generation
<10% cross-reactivity
1st Generation cehalosporins
Cephalexin (PO)
Cefazolin (IV)
2nd Generation Cephalosporins
Cefuroxime (PO,IV)
Cefoxitin (IV)
Cefotetan (IV)
Cefprozil (PO)
1st Generation Cephalosporins Spectrum: Good
MSSA (if can’t tolerate PCN)
Streptococci
1st Generation Cephalosporins Spectrum: Moderate
Some enteric GNRs
1st Generation Cephalosporins Spectrum: Poor
Enterococci
MRSA
Anaerobes
Pseudomonas
2nd Generation Cephalosporins Spectrum: Good
Some GNRs
Haemophilus influenzae
Neisseria
2nd Generation Cephalosporins Spectrum: Moderate
Strep
Staph
Anaerobes (cefotetan, cefoxitin)
2nd Generation Cephalosporins Spectrum: Poor
Enterococci
MRSA
Pseudomonas
Which cephalosporins are used for surgical prophylaxis in abdominal surgery?
Cefoxitin and Cefotetan
Which cephalosporins do not require renal adjustments?
Cefoxitin and Cefotetan
Which generation of cephalosporins does not cross the CNS?
1st Generation
Utility of 1st generation cephalosporins
Skin and soft tissue infxns, surgical prophylaxis, staph bloodstream infxns, endocarditis (MSSA)
Utility of 2nd generation cephalosporins
URTI, CAP, gonorrhea, surgical prophylaxis (cefotetan, cefoxitin)
CAP
Community acquired pneumonia
