The USMLE pharmacology assessment evaluates medical students' knowledge and understanding of pharmacological principles and their application in clinical scenarios. It consists of multiple-choice questions and clinical vignettes that assess topics such as drug mechanisms of action, pharmacokinetics...
1. A 38-year-old IV drug-user presents with a two-week history of progressive dysphagia,
odynophagia, and fever. The most likely cause of this patient’s condition is most appropriately
treated with an agent that does which of the following?
A) Creation of pores in the ergosterol membrane
B) Inhibition of 14α-demethylase
C) Inhibition of squalene epoxidase
D) Inhibition of microtubules
E) Inhibition of synthesis of 1,3-β-glucan
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The answer is B.
IV drug-use = ↑↑ risk of HIV/AIDS.1
The most common cause of infectious esophagitis in HIV/AIDS is candida.2
The treatment for candidal esophagitis is oral fluconazole 200 to 400 mg per day for 14 to 21
days.3 (You do not need to know doses for the USMLE)
Azole anti-fungals inhibit ergosterol synthesis by inhibiting 14α-demethylase. Ergosterol is the
cholesterol equivalent in fungi.4
Terbinafine inhibits lanosterol synthesis by inhibiting squalene epoxidase. Lanosterol is the
precursor to ergosterol.5, 6 Topical terbinafine is a first-line treatment for tinea pedis.7 Oral
terbinafine is a first-line treatment for onychomycosis (fungal nail infection).8
Creation of pores in the ergosterol membrane refers to nystatin9 and amphotericin B.10
Nystatin, or an azole, may be used in topical suspension (mouthwash) form as first-line treatment
for oropharyngeal candidiasis11, 12, 13, however esophageal candidiasis is treated with oral azole.3
Amphotericin B is an extremely hard-hitting anti-fungal used in various CNS and disseminated
fungal infections.14 On the USMLE, only choose this drug only if the patient is very sick, often with
high fever and chills/rigors (i.e., suggesting fungemia and/or CNS involvement).
Inhibition of microtubules refers to griseofulvin, which may be used orally to treat tinea capitis.15
Inhibition of synthesis of 1,3-β-glucan refers to the echinocandins, such as caspofungin, which is
used in the treatment of invasive aspergillosis in patients who cannot receive, or who fail,
voriconazole therapy.16, 17
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Bottom line: You must know the mechanisms of action of the anti-fungals to score above
the 220s on the USMLE Step 1. Understand the basic uses of each agent as well.
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