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Antibiotics

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Topic updated on 08/23/17 10:54am

 Overview by Mechanism
 
Antibiotic Grouping by Mechanism
Cell wall synthesis inhibitors
  • Penicillins
  • Cephalosporins
  • Vancomycin
  • Beta-lactamase inhibitors
  • Carbepenems
  • Aztreonam
  • Polymycin
  • Bacitracin
 
Protein synthesis inhibitors Inhibit 30S subunit
  • Aminoglycosides (gentamycin)
  • Tetracyclines

Inhibit 50S subunit
  • Macrolides 
  • Chloramphenicol
  • Clindamycin
  • Linezolid
  • Streptogramins
DNA synthesis inhibitors
  • Fluoroquinolones
    Metronidazole
RNA synthesis inhibitors
  • Rifampin
Mycolic acid synthesis inhibitors
  • Isoniazid
Folic acid synthesis inhibitors
  • Sulfonamides
  • Trimethoprim
 
Classification & Indications
 
Cell Wall Synthesis Inhibitors
Penicillins
(Bactericidal: inhibits bacterial cell wall synthesis via competitive inhibition of the transpeptidase enzyme)
Class Name of Drug(s) Indications
Penicillin
  • Penicillin G
  • Aqueous (crystalline) penicillin G
  • Procaine penicillin G
  • Benzathine penicillin G
  • Penicillin V
  • S. pnuemoniae
  • S. pyogenes (group A strep)
  • N. meningitidis
  • T. pallidum
  • L. monocytogenes
  • A. israelii
  • P. multocida
Aminopenicillins
  • Ampicillin
  • Amoxicillin
  • ↑ gram-negative coverage
  • Enterococci (group D strep)
  • All others listed above
Penicillinase-resistant penicillins 
  • Methicillin
  • Nafcillin
  • Oxacillin
  • Cloxacillin
  • Dicloxacillin
  • Penicillinase-producing S. aureus
  • All others listed above
Antipseudomonal penicillins 
  • Carbenicillin
  • Ticarcillin
  • Piperacillin
  • P. aeruginosa
  • Anaerobic bacteria
  • All others listed above
Cephalosporins
(Bactericidal: inhibits bacterial cell wall synthesis via competitive inhibition of the transpeptidase enzyme)
1st generation
  • Cefazolin
  • Cephalexin
  • Gram-positives
  • Some gram-negatives
  • Skin infection prophylaxis
2nd generation
  • Cefoxitin
  • Cefaclor
  • Cefuroxime
  • Gram-positives
  • Improved gram-negative coverage
  • Anaerobes

3rd generation

  • Ceftriaxone
  • Cefotaxime
  • Ceftazidime
  • Serious gram-negative infections
  • Meningitis
  • Pseudomonas
4th generation
  • Cefepime
  • Same coverage as cephalosporins + expanded Pseudomonas coverage + expanded gram-positive coverage
5th generation
  • Ceftaroline
  • Expanded gram-positive and gram-negative coverage, non-suitable coverage of Pseudomonas
Other Cell Wall Inhibitors

Vancomycin                  (bactericidal: inhibits bacterial cell wall synthesis by disrupting peptioglycan cross linking)

  • Vancomycin
  • MRSA
  • Patients with PCN or ceph allergies
  • S aureus
  • S epidermidis
  • C. difficile


Beta-lactamase inhibitors
(beta-lactamse inhibitors that  prevent the degradation of beta-lactam antibiotics)
  • Clavulanic acid
  • Sulbactam
  • Tazobactam
  • Gram-positive
  • S. aureus
  • S. epidermis
  • Gram-negative
  • E. coli
  • Klebsiella
Carbapenems  
(Inhibits bacterial cell wall synthesis)
  • Imipenem (+ cilastatin)
  • Meropenem
  • Doripenem
  • Ertapenem
  • Broadest activity of any antibiotic (does NOT cover MRSA, Mycoplasma, and some Pseudomonas)
Aztreonam 
(inhibits bacterial cell wall synthesis)
  • Aztreonam
  • Gram-negative rods
  • Aerobes
  • Difficult-to-treat hospital-acquired infections
Polymyxins
  • Polymyxin B
  • Polymyxin E
  • Topical gram-negative infections
Bacitracin
  • Bacitracin
  • Topical gram-positive infections
Protein Synthesis Inhibitors
Anti-30S Ribosomal Subunit
Aminoglycosides
(bactericidal)
  • Gentamicin
  • Neomycin
  • Amikacin
  • Tobramycin
  • Streptomycin
  • Severe gram-negative infections
  • Aerobes only
Tetracyclines                    (bacteriostatic)
  • Tetracycline
  • Doxycycline
  • Minocycline
  • Demeclocycline
  • Chlamydia
  • Rickettsia
  • Bacteria without peptidoglycan cell walls
  • Spirochetes
  • V. cholerae
  • H. pylori
Anti-50S Ribosomal Subunit
Macrolides  
  • Erythromycin
  • Azithromycin
  • Clarithromycin
  • Outpatient URI, LRI
  • Atypical pneumonia
  • STDs
  • Gram-positive cocci
Chloramphenicol   
(bacteriostatic)
  • Chloramphenicol
H. influenzae
Bacterial meningitis
Brain abscess
Bacteroides fragilis
Clindamycin  
(bacteriostatic)
  • Clindamycin
Anaerobes above the diaphragm
Female GU
TSS
Linezolid                              (variable)
  • Linezolid
Resistant gram-positives (MRSA, VRE)
Streptogramins
  • Quinupristin
  • Dalfopristin
  • VRE
  • GAS and S. aureus skin infections
  • Note: bacteriocidal when used together
DNA Synthesis Inhibitors
Fluoroquinolones
(Bactericidal: inhibit DNA gyrase enzyme, inhibiting DNA synthesis)
1st generation  
  • Nalidixic acid
  • Gram-negative UTIs
2nd generation 
  • Ciprofloxacin
  • Norfloxacin
  • Enoxacin
  • Ofloxacin
  • Levofloxacin
  • Gram-negative UTIs
  • Gram-negative GI tract
  • Pseudomonas
3rd generation 
  • Gatifloxacin
  • As above + gram-positives
4th generation 
  • Moxifloxacin
  • Gemifloxacin
  • As above + gram-positives + anaerobes
Other DNA Inhibitors
Metronidazole              (bacteridical: metabolic byproducts disrupt DNA)
  • Metronidazole (Flagyl)
  • Bacteria AND protozoa
  • Anaerobes below the diaphragm
  • C. difficile
  • H. pylori
RNA Synthesis Inhibitors
Rifampin   
(bactericidal: inhibits RNA transcription)
  • Rifampin
  • TB
  • Leprosy
  • H. influenzae prophylaxis
  • Antistaphylococcal
Mycolic Acids Synthesis Inhibitors
Isoniazid  
  • Isoniazid
  • TB
  • Latent TB
Folic Acid Synthesis Inhibitors
Sulfonamides  
  • Sulfamethoxazole (SMX)
  • Sulfisoxazole
  • Sulfadiazine
  • Respiratory (S. pneumoniae, H. influenzae)
  • GI (enterics)
  • UTIs
  • PCP and T. gondii
Trimethoprim
  • Trimethoprim
  • See Sulfonamides
Pyrimethamine 
  • Pyrimethamine
  • Malaria
  • T. gondii
Miscellaneous   
Drugs Mechanism of Action Indications and Side Effects
Pyrazinamide
  • Uncertain mechanism: potentially accumulates in cells dsirupting membrane potential and fatty acid synthesis
  • Part of RIPE therapy for TB
  • Can cause hyperuricemia and hepatoxicity
Ethambutol
  • Inhibits arabinosyltransferase (inhibiting production of mycobacterium cell wall)
  • Part of RIPE therapy for TB and used for M. avium-intracellulare
  • Can cause optic neuropathy (red-green color blindness)
Daptomycin
  • Lipopeptide that disrupts cell membrane
  • Multi-resistant gram-positives such as MRSA and VRE
  • Can cause myopathy (elevated CK and rhabdomyolysis


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Qbank (2 Questions)

TAG
(M1.MC.8) A 21-year-old sexually active male complains of fever, pain during urination, and inflammation and pain in the right knee. A culture of the joint fluid shows a bacteria that does not ferment maltose and has no polysaccharide capsule. The physician orders antibiotic therapy for the patient. The mechanism of action of action of the medication given blocks cell wall synthesis, which of the following was given? Topic Review Topic

1. Chloramphenicol
2. Gentamicin
3. Ciprofloxacin
4. Ceftriaxone
5. Trimethoprim

PREFERRED RESPONSE ▶
TAG
(M1.MC.77) A 56-year-old woman with no significant past medical history presents to her primary care physician with a cough. She notes that the cough began two weeks ago and has been worsening. Over the past several days, she has developed low-grade fevers, and the cough has become productive of green mucus. Her physician decides to treat her with a "Z-pack," which is a 5-day course of azithromycin, and orders a chest radiograph, which is shown in Figure A. Which of the following antibiotics has the same target site as azithromycin? Topic Review Topic
FIGURES: A          

1. Ciprofloxacin
2. Chloramphenicol
3. Bacitracin
4. Gentamycin
5. Vancomycin

PREFERRED RESPONSE ▶

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This video describes the mechanism of action of antibiotics.
2/14/2015
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