Classification of Antibiotics

Mechanisms of Antibiotics

  • Antibiotics that inhibit cell wall synthesis or function

Beta Lactams: Penicillins, Cephalosporins, Carbapenems, and Monobactams.
Vancomycin.
Daptomycin.
Polypeptides: Bacitracin and Colistin.

  • Antibiotics that inhibit nucleic acid synthesis or function

Quinolones.
TMP/Sulfa.
Nitrofurantoin.
Metronidazole.

  • Antibiotics that inhibit protein synthesis

Macrolides.
Clindamycin.
Tetracyclines.
Chloramphenicol.
Linezolid.
Streptogramins.
Tigecycline.
Aminoglycosides.


Penicillins
Beta-Lactamases are enzymes that can cleave the beta-lactam ring. They are most common in gram negative bacteria. Beta-Lactamase Inhibitors include: Clavulanic Acid, Sulbactam, and Tazobactam.
Adverse effects include thrombocytopenia and AIN.
Penicillin G
Streptococci, Enterococcus Faecalis, Listeria, Peptostreptococcus, and Actinomyces.
Ampicillin and Amoxicillin
Streptococci (excluding Viridans), Enterococcus Faecalis, Listeria, susceptible Gram Negatives (E. coli, Proteus, Salmonella, Shigella, and H. flu), Peptostreptococcus, and Actinomyces.
Ampicillin/Sulbactam (Unasyn)
MSSA, Streptococci (excluding Viridans), Enterococci, Listeria, Gram Negatives (excluding Pseudomonas and Stenotrophomonas), and Anaerobes.
Amoxicillin/Clavulanic Acid (Augmentin)
MSSA, Streptococci (excluding Viridans), Enterococci, Listeria, Gram Negatives (excluding Pseudomonas, Stenotrophomonas, and Acinetobacter), and Anaerobes.
Nafcillin, Oxacillin, and Dicloxacillin
Staphylococci (excluding MRSA) and Streptococci (excluding Viridans).
Piperacillin/Tazobactam (Zosyn)
Staphylococci (excluding MRSA), Streptococci (excluding Viridans), Enterococci, Listeria, Gram Negatives, and Anaerobes.


Cephalosporins
Cephalosporins have no activity against Enterococci or Listeria.
1st Generation: Cefazolin and Cephalexin
MSSA, Streptococci, and susceptible Gram Negatives (E. coli, Klebsiella, and Proteus).
2nd generation: Cefuroxime
MSSA, Streptococci, and susceptible Gram Negatives (E. coli, Klebsiella, Proteus, and H. flu).
2nd generation: Cefoxitin and Cefotetan
MSSA, Streptococci, susceptible Gram Negatives (E. coli, Klebsiella, Proteus, and H. flu), and Anaerobes.
3rd Generation: Cefpodoxime, Ceftriaxone, and Ceftazidime
MSSA, Streptococci, and Gram Negatives (excluding Pseudomonas, Stenotrophomonas, and Acinetobacter). Ceftazidime does cover Pseudomonas and Acinetobacter.
4th Generation: Cefepime
MSSA, Streptococci, and Gram Negatives (excluding Stenotrophomonas).
Adverse effects include lowering seizure threshold.
5th Generation: Ceftaroline
MRSA, Streptococci, and Gram Negatives (excluding Pseudomonas, Stenotrophomonas, and Acinetobacter).


Carbapenems
Adverse effects include lowering seizure threshold.
Imipenem/Cilastatin and Meropenem
Gram Positives (excluding MRSA and Enterococcus Faecium), Gram Negatives (excluding Stenotrophomonas and Acinetobacter), and Anaerobes.
Ertapenem
Gram Positives (excluding MRSA and Enterococci), Gram Negatives (excluding Pseudomonas, Stenotrophomonas, and Acinetobacter), and Anaerobes.

  
Monobactams
Aztreonam
Gram Negatives (excluding Stenotrophomonas and Acinetobacter).


Vancomycin
Gram Positives and Anaerobes (excluding Bacteroides and Fusobacterium).
It has poor CNS penetration.
Adverse effects include red man syndrome, neutropenia, ototoxicity, and nephrotoxicity.


Daptomycin
MRSA and VRE.
It is not effective in treating pneumonia (it is inactivated by pulmonary surfactant).
Adverse effects include myopathy, neuropathy, and eosinophilic pneumonia.


Colistin (Polymyxin E)
Pseudomonas, ESBL, Stenotrophomonas, and Acinetobacter.
Adverse effects include nephrotoxicity and neurotoxicity.


Quinolones
They should not be taken simultaneously with iron, calcium, or antacids.
They have poor CNS penetration.
Adverse effects include QT prolongation, exacerbation of myasthenia gravis, and tendonopathy.
Ciprofloxacin
Gram Negatives (excluding Stenotrophomonas and Acinetobacter) and Atypicals (excluding Rickettsia).
Levofloxacin
Gram Positives (excluding MRSA, Viridans, and Enterococcus Faecium), Gram Negatives (excluding Stenotrophomonas and Acinetobacter), and Atypicals (excluding Rickettsia).
Moxifloxacin
Gram Positives (excluding MRSA, Viridans, and Enterococcus Faecium), Gram Negatives (excluding Pseudomonas, Stenotrophomonas, and Acinetobacter), Anaerobes (excluding Clostridium spp and Bacteroides), and Atypical (excluding Rickettsia).
It has less renal clearance than Ciprofloxacin and Levofloxacin, so it should not be used to treat urinary tract infections.


TMP/Sulfa
MSSA, Community Acquired MRSA, Streptococcus Pneumoniae, Nocardia, Listeria, and Gram Negatives (excluding Pseudomonas and Acinetobacter) which have 30-60% susceptibility.


Metronidazole
Clostridium Spp and Bacteroides.
Adverse effects include metallic taste and Disulfram effect (Pt on Metronidazole who consumes alcohol develops skin flushing, tachycardia, headache, nausea, and vomiting).


Macrolides
Adverse effects include QT prolongation, exacerbation of myasthenia gravis, and hepatic dysfunction.
Erythromycin
MSSA, Streptococci (excluding Viridans), C. Diphtheriae, Listeria, Bordetella Pertussis, Anaerobes (excluding Bacteroides), and Atypicals (excluding Rickettsia).
Azithromycin and Clarithromycin
MSSA, Streptococci (excluding Viridans), Listeria, Gram Negative Coccobacilli, Anaerobes (excluding Bacteroides), and Atypicals (excluding Rickettsia).
Fidaxomicin
Clostridium Difficile.


Clindamycin
MSSA, community acquired MRSA, Streptococci (excluding Viridans), and Anaerobes (excluding Bacteroides).


Doxycycline
Community Acquired MRSA, Streptococci (excluding Viridans), Listeria, N. Meningitidis, E. Coli, Brucella, M. Catarrhalis, H. flu, Anaerobes (excluding Bacteroides), and Atypicals.


Chloramphenicol
Streptococci, Listeria, N. Meningitidis, E. Coli, Brucella, M. Catarrhalis, H. flu, Anaerobes and Atypicals.
Adverse effects include aplastic anemia.


Linezolid
MRSA and VRE.
Adverse effects include Myelosuppression, lactic acidosis, optic neuritis, and serotonin syndrome.


Streptogramins
Synercid
MRSA and Vancomycin-Resistant Enterococcus Faecium.
It requires a central line.


Tigecycline
MRSA and VRE.
Adverse effects include elevated LFTs and pancreatitis.


Aminoglycosides
They are commonly used for serious infections caused by enteric GNRs.
They are also used in combination with another antibiotic to cover Pseudomonas.
They are not used as monotherapy for gram positive infections, but are sometimes used in combination with a beta-lactam or Vancomycin for synergy, especially for endocarditis.
Serious toxicities include ototoxicity, nephrotoxicity, and neuromuscular blockade.
Gentamicin
Tobramycin
Amikacin