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Snapshot
  • A 48-year-old woman presents to the urgent care clinic after finding a tick on her leg. She had recently gone camping in New England. She pulled off the tick on her own but was not able to show the tick to the physician. She denies having any rashes or symptoms. However, she is concerned about Lyme disease. She is given the first-line treatment for Lyme disease and reassured. She is advised to wear sunscreen or avoid the sun while on this treatment. (Lyme disease)
Introduction
  • Drugs
    • tetracycline
    • doxycycline
    • minocycline
  • Mechanism of action
    • reversibly binds to the bacterial ribosomal 30S subunit, inhibiting the elongation phase of RNA synthesis by preventing the attachment of aminoacyl tRNA to mRNA acceptor site
    • accumulates inside bacterial cells, making it good for intracellular agents
    • bacteriostatic
    • absorption inhibited by milk and antacids 
    • eliminated via stool
  • Mechanism of resistance
    • bacterial transport pumps will prevent accumulation of drug inside the cell by increasing efflux out or decreasing uptake of the drug
  • Clinical use
    • infections
      • gram-positive aerobes
      • gram-negative rods
      • spirochetes
      • atypical respiratory pathogens
        • Mycoplasma
        • Legionella
        • Chlamydophila
      • anaerobes
      • tick-mediated infections
    • dermatologic conditions
      • acne
      • rosacea
    • no activity against Pseudomonas
    • high-yield uses
      • doxycycline is used for
        • Chlamydia trachomatis
        • tick-borne infections (Rickettsia, Borrelia, Ehrlichia, and Anaplasma)
  • Adverse effects 
    • gastrointestinal upset (most common)
    • discoloration of teeth
    • inhibition of bone growth in children
    • photosensitive rash
    • teratogenic and contraindicated in pregnancy
 

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Questions (2)
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(M1.MC.14.1) A 45-year-old female presents to her family medicine physician complaining of fever for 2.5 weeks, enlarged lymph nodes in her right axilla, and a small bump that formed when her recently adopted cat bit her 3 weeks ago. Based on her symptoms and history, the physician prescribed an antiobitic to treat her current illness. Several days later, she experienced erythema and itchiness on her shoulders, arms, and back after spending only several minutes a day in the sun (Figure A). Which of the following is the mechanism of action of the antibiotic prescribed? Tested Concept

QID: 106430
FIGURES:
1

Blocks the peptidyltransferase on the 50S ribosomal subunit

14%

(7/50)

2

Forms toxic free radicals that damage DNA

8%

(4/50)

3

Binds to the 30S ribosomal subunit preventing aminoacl-tRNA attachment

56%

(28/50)

4

Binds to PBP3 preventing the cross-linking of the peptidoglycan layer

8%

(4/50)

5

Blocks peptide translocation by binding to the 23S rRNA of the 50S ribosomal subunit

8%

(4/50)

L 1 D

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