WBR0046

Author	[[PageAuthor::William J Gibson (Reviewed by Rim Halaby, M.D. [1] and Yazan Daaboul)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology, MainCategory::Pharmacology
Sub Category	SubCategory::Pulmonology, SubCategory::General Principles
Prompt	[[Prompt::A 27-year-old man presents to his primary care physician complaining of dyspnea and fatigue of one week duration. Over the past week, he has been experiencing gradually worsening new-onset fatigue and dyspnea. Despite his symptoms, the patient confirms that his condition is "not so bad". His past medical history is not significant. He denies any allergies or use of medications. His blood pressure is 112/82 mmHg, heart rate is 72/min, temperature is 101 F (38.3 C), respiratory rate is 24/min, and oxygen saturation is 92% on room air. Physical examination is remarkable for the presence of diffuse crackles over both lung fields. Chest xray is ordered; it shows diffuse interstitial infiltrates over both lung fields with no focal consolidation. Which of the following is the most appropriate treatment for this patient's condition?]]
Answer A	AnswerA::Chloramphenicol
Answer A Explanation	[[AnswerAExp::Chloramphenicol is not the drug of choice for Mycoplasma pneumoniae infection.]]
Answer B	AnswerB::Trimethoprim-Sulfamethoxazole
Answer B Explanation	[[AnswerBExp::Trimethoprim-Sulfamethoxazole (TMP-SMX) is not the drug of choice for Mycoplasma infection. TMP-SMX is often used for simple UTI and Pneumocystis jirovecii infection in HIV-positive patients. TMP-SMX may also be used as prophylaxis for Pneumocystis jirovecii and Toxoplasma gondii in HIV-positive patients.]]
Answer C	AnswerC::Azithromycin
Answer C Explanation	[[AnswerCExp::Azithromycin is a macrolide antibiotic that blocks the 50s ribosomal subunit and can be used to treat Mycoplasma pneumoniae infection.]]
Answer D	AnswerD::Penicillin
Answer D Explanation	[[AnswerDExp::Penicillin is ineffective against Mycoplasma infections because mycoplasma lacks a peptidoglycan cell wall.]]
Answer E	AnswerE::Aztreonam
Answer E Explanation	[[AnswerEExp::Aztreonam, a beta-lactam antibiotic resistant to beta-lactamases, is ineffective against Mycoplasma infections because mycoplasma lacks a peptidoglycan cell wall.]]
Right Answer	RightAnswer::C
Explanation	[[Explanation::The patient is suffering from a case of atypical pneumonia, a respiratory infection which often causes systemic symptoms such as fever, headache and myalgia. Atypical pneumonia differs from typical pneumonia in that atypical pneumonias often does not respond to common antibiotics (eg sulfonamides, or beta-lactams), does not show signs of consolidation, nor does it give rise to leukocytosis. On chest xray, patients often show diffuse interstitial infiltrates which conveys the appearance of a more severe infection than the patient’s symptoms suggest. Because patients often have mild symptoms, atypical pneumonia is alternatively referred to as “walking pneumonia". Atypical pneumonia is most often caused by Mycoplasma pneumoniae, which usually infects older children and young adults less than 30 years of age. Mycoplasma pneumoniae can be treated with macrolides (eg azithromycin) or tetracyclines. Educational Objective: Mycoplasma pneumoniae can be treated with macrolides (eg azithromycin) or tetracyclines. References: First Aid 2014 page 145]]
Approved	Approved::Yes
Keyword	WBRKeyword::Microbiology, WBRKeyword::Mycoplasma, WBRKeyword::Bacteria, WBRKeyword::Pneumonia, WBRKeyword::Infection, WBRKeyword::Antibiotics, WBRKeyword::Drug, WBRKeyword::Drugs, WBRKeyword::Pharmacology
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