questions 4

Aminoglycosides

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Topic updated on 01/20/17 8:23pm

 
Overview of Antibiotic Mechanisms
 
Introduction
  • Classification
    • antibiotic
      • anti-ribosomal 
        • anti-30S ribosomal subunit
          • aminoglycosides
  • Drugs
    • gentamicin
    • neomycin
    • amikacin
    • tobramycin
    • streptomycin
Mechanism
  • Action
    • bactericidal
    • binds to 30S ribosomal subunit 
      • inhibit formation of initiation complex 
      • Aminoglycosides inhibit initiAtion
      • cause misreading of mRNA
    • accumulates inside bacteria via O2-dependent uptake
      • cannot be used against anaerobes
      • "aminO2glycoside"
  • Resistance
    • via modification by acetylation, adenylation, or phosphorylation 
    • Aminglycoside resistance is by Acetylation
Uses
  • Severe infections with Gram-negative rods
    • aerobes only
    • synergistic with β-lactam antibiotics
  • Gentamicin
    • most widely used
    • nosocomial infections
  • Neomycin
    • toxic
    • topically for skin infections
    • bowel surgery
  • Amikacin
    • broadest spectrum
    • nosocomial infections
  • Tobramycin
    • Pseudomonas aeruginosa
  • Streptomycin
    • oldest aminoglycoside
    • resistance is common
Adverse effects
  • Nephrotoxicity
    • especially when used with cephalosporins
  • Ototoxicity 
    • especially when used with loop diuretics
  • Avoid in pregnancy
    • teratogen
    • ototoxicity
  • Neuromuscular block in very high doses


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Qbank (2 Questions)

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(M1.MC.3) You are treating a neonate with meningitis using ampicillin and a second antibiotic, X, that is known to cause ototoxicity. What is the mechanism of antibiotic X? Topic Review Topic

1. It binds the 50S ribosomal subunit and inhibits peptidyltransferase
2. It binds the 50S ribosomal subunit and inhibits formation of the initiation complex
3. It binds the 30s ribosomal subunit and inhibits formation of the initiation complex
4. It binds the 30s ribosomal subunit and reversibly inhibits translocation
5. It binds the 50s ribosomal subunit and reversibly inhibits translocation

PREFERRED RESPONSE ▶
TAG
(M1.MC.4754) A 67-year-old African American male presents to the emergency room complaining of nausea and right flank pain. He reports that these symptoms have worsened over the past two days. His past medical history is notable for congestive heart failure, hypertension, hyperlipidemia, and diabetes mellitus. He currently takes aspirin, losartan, metoprolol, atorvastatin, hydrochlorothiazide, furosemide, and metformin. He is allergic to fluoroquinolones. His temperature is 102.9°F (39.4°C), blood pressure is 100/50 mmHg, pulse is 120/min, and respirations are 28/min. On exam, he demonstrates right costovertebral angle tenderness. Urinalysis reveals 30 WBCs/hpf and positive leukocyte esterase. He is admitted and started on a broad-spectrum combination intravenous antibiotic. He recovers well and is discharged with plans to follow up in 2 weeks. At his follow-up, he reports that he has developed transient visual blurring whenever he turns his head to the right or left. He also reports that he has fallen at home multiple times. What is the mechanism of action of the drug that is most likely responsible for this patient’s current symptoms? Topic Review Topic

1. Inhibition of ribosomal 30S subunit
2. Inhibition of ribosomal 50S subunit
3. Inhibition of dihydropteroate synthase
4. Inhibition of transpeptidase
5. Inhibition of DNA gyrase

PREFERRED RESPONSE ▶
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