View source for WBR0046

{{WBRQuestion
|QuestionAuthor=William J Gibson
|ExamType=USMLE Step 1
|MainCategory=Microbiology, Pharmacology
|SubCategory=Pulmonology, General Principles
|MainCategory=Microbiology, Pharmacology
|SubCategory=Pulmonology, General Principles
|MainCategory=Microbiology, Pharmacology
|SubCategory=Pulmonology, General Principles
|MainCategory=Microbiology, Pharmacology
|MainCategory=Microbiology, Pharmacology
|SubCategory=Pulmonology, General Principles
|MainCategory=Microbiology, Pharmacology
|SubCategory=Pulmonology, General Principles
|MainCategory=Microbiology, Pharmacology
|SubCategory=Pulmonology, General Principles
|MainCategory=Microbiology, Pharmacology
|SubCategory=Pulmonology, General Principles
|MainCategory=Microbiology, Pharmacology
|MainCategory=Microbiology, Pharmacology
|SubCategory=Pulmonology, General Principles
|Prompt=A 20 year old woman presents to her primary care physician complaining of dyspnea and malaise.  Over the past week she has experienced increasing dyspnea, bronchitis and fatigue which limits her otherwise vigorous exercise but does not interfere with daily activities.  She denies abnormal sputum production and any significant past medical history.  On examination, her pulse is 72, temperature of 101 F (38.3 C), respiratory rate of 22 and oxygen saturation of 94% on room air.  Cardiac examination is normal but respiratory exam reveals diffuse crackles.  What antibiotic regimen should this patient be started on?
|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 it does not respond to common antibiotics (eg sulfonamides, or beta-lactams), does not show signs of consolidation, nor leukocytosis.  On chest X-ray, patients often show diffuse interstitial infiltrate 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 Pneumonia which usually occurs in older children and young adults (patients <30 years old).  Mycoplasma Pneumonia is a mere 0.3 um in size and is the only bacteria which does not possess a cell wall.  Mycoplasma pneumonia can be treated with macrolides (eg erythromycin) or tetracyclines.
Educational objective: Mycoplasma pneumonia can be treated with macrolides (eg erythromycin) or tetracyclines.

References: 
	First Aid 2012 pg 170.
Tags: #Microbiology #Pharmacology
|AnswerA=Chloramphenicol
|AnswerAExp=False.  Chloramphenicol is not the drug of choice for Mycoplasma infection.  Chloramphenicol is known for causing Gray baby syndrome.
|AnswerB=Trimethoprim-Sulfamethoxazole (Bactrim)
|AnswerBExp=False.  TMP-SMX is not the drug of choice for Mycoplasma infection.  TMP-SMX is often used for simple UTIs/cystitis.
|AnswerC=Erythromycin
|AnswerCExp=True.  See explanation.
|AnswerD=Penicillin
|AnswerDExp=False.  Penicillin is ineffective against Mycoplasma infections because mycoplasma lacks a peptidoglycan cell wall.
|AnswerE=Aztreonam
|AnswerEExp=False.  Aztreonam, a beta-lactam antibiotic resistant to beta-lactamases, is ineffective against Mycoplasma infections because mycoplasma lacks a peptidoglycan cell wall.
|RightAnswer=C
|Approved=Yes
}}