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Antibiotics 101. Puja Van Epps 1/20/14. Beta-lactams. Core PCN structure. Core Cephalosporin structure. Beta-lactams. Beta-lactamases are enzymes produced by some bacteria that provide resistance against beta lactams through hydrolysis of the β- lactam ring. Natural Penicillins.

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Antibiotics 101

Antibiotics 101

Puja Van Epps


Beta lactams

Core PCN structure

Core Cephalosporin structure

Beta lactams1

  • Beta-lactamases are enzymes produced by some bacteria that provide resistance against beta lactams through hydrolysis of the β-lactam ring

Natural penicillins
Natural Penicillins

  • Bicillin L-A (Penicillin G benzathine) – IM only

  • Penicillin G (IV)

  • Penicillin V = PO

Natural penicillins1
Natural Penicillins

Bicillin: Primary, secondary, latent and late latent syphillis

PCN G: Neurosyphillis; systemic infection due to susceptible bacteria (Streptococci)

PCN V: Group A strep pharyngitis

Anti staphylococcal penicillins
Anti-staphylococcal Penicillins

  • Nafcillin, oxacillin, methicillin, dicloxacillin (PO)

  • Penicillinase is a specific type of β-lactamase, showing specificity for Penicillins

  • First β-lactamase to be identified; PCN R in S. aureus

  • Major Uses:

    Methicillin-susceptible S. aureus or Coagulase Negative Staph; PCN-susceptible strains of Streptococci

  • No gram negative activity


  • Ampicillin/amoxicillin; Augmentin (Amox-Clav); Unasyn (Amp-Sulbactam)

  • Amp/amox – Great for susceptible streps and enterococcus; very limited GN activity; cover anaerobes

  • Addition of Clavulanate or Sulbactam enhances Gram negative activity

  • No activity against MSSA without the beta-lactamase inhibitor.


  • Important holes in coverage

  • Pseudomonas sp.

  • Atypical gram negatives – mycoplasma pneumoniae, chlamydia pneumoniae, legionella sp.

  • Enterobacter sp.

  • If susceptible Ampicillin is the DOC for Enterococcus and Listeria

Anti pseudomonal penicillins
Anti-Pseudomonal Penicillins

  • Ticarcillin, Ticar-Clav, Piperacillin, Pip-Tazo

  • Generally good gram positive, gram negative and anaerobic coverage

  • Ticarcillin and Piperacillin without their beta-lactamase inhibitor DO NOT cover MSSA

  • Important holes in coverage: MRSA (ESBL+, KPC+, or other resistant GN)

  • Stenotrophomonas maltophilia – Ticar-Clav is second line, Pip/Tazo does not cover.


  • 5 generations, increasing gram negative coverage with each generation

First generation cephalosporins
First Generation Cephalosporins

  • Cefadroxil, Cephalexin (PO)

  • Cefazolin (IV)

First generation cephalosporins1
First Generation Cephalosporins

  • Important holes in coverage –

  • MRSA, Enterococcus, Pseudomonas, anerobes

Second generation cephalosporins
SecondGeneration Cephalosporins

  • Cefuroxime (IV, PO), Cefotetan (IV), Cefoxitin (IV)

  • In addition to the coverage of 1st generation

    -H. influenzae, M. catarrhalis, Neisseria sp., and anearobic coverage (variable)

  • Important holes in coverage:

    - MRSA, Enterococcus, Pseudomonas

Third generation cephalosporins
Third Generation Cephalosporins

  • Ceftriaxone, Cefotaxime, Ceftazadime (IV)

  • Cefixime, Cefdinir (PO)

  • In general less active against gram-positive aerobes than previous generations, but have greater activity against gram-negatives

  • Cefotaxime and Ceftriaxone have the best gram + coverage in the group

  • Only Ceftazadime covers Pseudomonas

Third generation cephalosporins1
Third Generation Cephalosporins

  • Major holes in coverage –

    - Enterococcus, MRSA, Pseudomonas (except Ceftazidime), +/- Acinetobacter, Listeria

  • Ceftazidime crosses BBB, Ceftriaxone in inflamed meninges

Fourth generation cephalosporins
Fourth Generation Cephalosporins

  • Cefepime (IV)

    • gram-positives: similar to first generation

    • gram-negatives: broad, including Pseudomonas

    • Major holes: MRSA, poor anaerobic coverage, listeria

    • Crosses BBB

Fifth generation cephalosporin
Fifth Generation Cephalosporin

  • Ceftaroline (IV)

  • Major advantage:

    - MRSA

    Major holes in coverage:

    - Pseudomonas, enterococcus and anaerobes


Cephalosporin review
Cephalosporin Review

  • Antipseudomonal –

    Ceftazadime and Cefepime

  • Anti-MRSA –


  • Anti-Enterococcal –

    None (Ceftaroline has in-vitro activity against E. faecalis)

  • Enterobacter sp. can develop resistance to cephalosporins during treatment, therefore not the treatment of choice


  • Ertapenem, Doripenem, Imipenem, Meropenem

  • Broadest spectrum of activity

  • Have activity against gram-positive and gram-negative aerobes and anaerobes

  • Bacteria not covered by carbapenems include MRSA, VRE, MR coagulase-negative staph

  • Additional ertapenem exceptions:

    • Pseudomonas, Acinetobacter, Enterococcus


  • Major holes in coverage:

    - Atypicals (Legionella, Mycoplasma) , MRSA, VRE, Stenotrophomonasmaltophilia, KPC+

  • Ertapenem does not cover:

    - Pseudomonas, Acinetobacter, Enterococcus


  • Aztreonam: binds preferentially to PBP 3 of gram-negative aerobes

  • No gram positive or anaerobic activity

  • Major uses – Hospital acquired infections in patients with anaphylaxis to any beta lactams (does not have cross reactivity)

  • Important gram neg holes: Acinetobacter, ESBL+, KPC+


  • Ciprofloxacin, Levofloxacin, Moxifloxacin

  • Broad spectrum of activity, excellent bioavailability, tissue penetration

  • Cipro has poor gram + coverage

  • Disadvantages: resistance, expense, C diff

  • Advantages: Atypical coverage, Antipseudomonal (Cipro, Levo)


  • Gentamicin, Tobramycin, Amikacin

  • inhibit protein synthesis by irreversibly binding to 30S ribosome, bactericidal

  • For gram + use in combination with cell wall agents

  • Broad spectrum gram neg coverage including Pseudomonas and Acinetobacter

  • Also have mycobacterial coverage

Aminoglycosides adverse effects
Aminoglycosides – adverse effects

  • Nephrotoxicity

    • Nonoligouric renal failure from damage to the proximal tubules

    • Underlying CKD, Age, other nephrotixins, duration, high troughs

  • Ototoxicity

    • 8th cranial nerve damage - vestibular and auditory toxicity; irreversible

    • Related to duration of therapy (>2wks)


  • Clarithromycin, Erythromycin, Azithromycin

  • Inhibit protein synthesis by reversibly binding to the 50s ribosomal unit


  • Gram-Positive Aerobes – Clarithro>Erythro>Azithro

  • Gram-Negative Aerobes – Azithro>Clarithro>Erythro

    No activity against any Enterobacteriaceae or Pseudomonas

  • Anaerobes – activity against upper airway anaerobes

  • Atypical Bacteria – Excellent

  • Also cover – Mycobacterium avium complex, Campylobacter, Borrelia, Bordetella, Brucella.


  • Inhibits synthesis and assembly of the second stage of peptidoglycan polymers

  • Gram-positive bacteria: excellent coverage

  • Major uses:

    MRSA, MSSA (in PCN all), PCN R streptococci

  • No activity against gram-negatives or anaerobes

  • If MIC to Vancomycin in MRSA is ≥ 2, Do not use


Red-Man Syndrome

  • flushing, pruritus, rash

  • related to rate of infusion

  • resolves spontaneously

  • may lengthen infusion



  • Lipopeptide; binds to components of the cell membrane and causes rapid depolarization, inhibiting intracellular synthesis of DNA, RNA, and protein

  • Major uses

    - SAB, Right-sided IE caused by S. aureus, VRE

  • Indicated for SSTI, R sided IE

    Do not use for lung infections including MRSA PNA – pulmonary surfactant inhibits Daptomycin


  • Binds to the 50S ribosomal subunit near the surface interface of 30S subunit – causes inhibition of 70S initiation complex which inhibits protein synthesis

  • Active against wide range of Gram + bacteria, limited to no Gram negative or anearobic activity

  • Major uses –

    MRSA, VRE.

  • Major problem

    thrombocytopenia with prolonged use (>2wks), bacteriostatic (cidal against Enterococcus)


  • Binds to the 30S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis.

  • Broad spectrum of activity including –

    - MRSA, VRE, gram negatives (including resistant GN)

  • Major holes-

    The 3 P’s – Pseudomonas, Proteus and doesn’t get in the urine

  • Indicated for complicated SSTI, intra-abdominal infections, CAP

  • Major problems: GI issues, and shown to have increased mortality in serious infections – monotherapy only as a last resort.


Inhibits protein synthesis by binding exclusively to the 50S ribosomal subunit

Major uses

- MRSA (some isolates), anaerobic coverage


A positive D test indicates the presence of macrolide-inducible resistance to clindamycin produced by an inducible methylase that alters the common ribosomal binding site for macrolides, clindamycin


  • Doxycyline, Minocyline

  • Good gram pos, neg and anaerobic coverage

  • Major uses

    MRSA, anti-malarial prophylaxis, rickettsial infections, Borreliaburgdorferi

Trimethoprim tmx sulfa
Trimethoprim, TMX-Sulfa

  • Inhibit various steps within the folic acid biosynthetic pathway

  • Good gram pos and gram neg coverage (CA-MRSA)

  • Important uses: Pneumocystis, Stenotrophomonasmaltophilia, Nocardia

  • Major holes

    • Pseudomonas, anaerobes