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Review Question - QID 101475

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QID 101475 (Type "101475" in App Search)
A 14-year-old female notes that while her fever, malaise, and a sore throat have dissipated a week ago, her hacking cough persists. A chest radiograph (Figure A) demonstrates a streaky infiltrate in her right lung that appears much worse than the symptoms she is experiencing. A cold agglutination test conducted on her blood shows clumping together when placed at 4 degrees Celsius. Which of the following medications would best treat the agent causing her cough?
  • A

Vancomycin

6%

33/528

Isoniazid

10%

55/528

Ampicillin

6%

33/528

Azithromycin

74%

391/528

Pyrazinamide

2%

8/528

  • A

Select Answer to see Preferred Response

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The clinical presentation is indicative of Mycoplasma pneumoniae. The first-line antibiotic to treat M. pneumoniae infection is azithromycin.

Mycoplasma pneumoniae, which lack a cell wall, are the smallest bacteria capable of self-replication. Beta lactam antibiotics, such as penicillin, ampillicin, and ceftriaxone, that target the peptidoglycan cell wall of gram-positive bacteria, are ineffective against M. pneumoniae. Antibiotics that target the various protein machinery within M. pneumoniae are effective at targeting this bacterium - doxycycline (binds to 30S ribosomal subunit), azithromycin (binds the 50S ribosomal subunit), and ciprofloxacin (inhibits the bacterial topoisomerases). The chest radiograph of an infection with M. pneumoniae will tend to appear worse than the symptoms the patient is experiencing.

Stuckey-Schrock et al. discuss the diagnosis of community-acquired pneumonia, which is usually based on the history and physical examination of the child. The age of the child is the most helpful factor in determining the causative agent. When the diagnosis is unclear, a chest radiograph and viral testing may help narrow down the diagnosis.

Principi et al. report that, although some physicians question the efficacy of treating M. pneumoniae with antibiotics, most suggest that treatment with an antibiotic can alter the course of the infection. The antibiotics of choice are macrolides, tetracyclines, or fluoroquinolones. Macrolides should be given to children. In areas of low resistance to macrolides, no change in prescription is needed, but in areas of higher resistance, substitution of a tetracycline or fluoroquinolone should be considered to treat the infection.

Figure A shows a chest radiograph of a streaky infiltrate in the right lung caused by M. pneumoniae.

Incorrect Answers:
Answer 1: Vancomycin is a glycopeptide that prevents the synthesis of the peptidoglycan wall by binding to the D-alanyl-D-alanine end of the cell wall.
Answer 2: Isoniazid is used to treat M. tuberculosis by inhibiting mycolic acid synthesis.
Answer 3: Ampicillin inhibits transpeptidases which prevent the synthesis of the cell wall.
Answer 5: Pyrazinamide is also used to treat M. tuberculosis by inhibiting mycobacterial fatty-acid synthetase I.

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