HY USMLE Q#21 Derm/Pharm/Endo Step 1
HY USMLE Q#21 Pharm/Derm/ Micro ( Step 1 inspired by MEHLMAN YouTube video 1455)
A 38-year-old man went to the physician for a 1-week history of a lesion on his right leg. He lives with his four dogs and frequently uses yoga mats at the gym. The most appropriate therapy for this patient is which of the following?
A. Tubulin
B. RNA synthesis
C. Epoxidase
D. Demythelation
E. Carbohydrates
✅ Correct Answer = Choice D demythelization.
The above patient has ringworm, hence he has Tinea Coporis. Hence, we will have to use topical azoles to treat this infection. Hence, the enzyme 14-alpha-demethylase is inhibited, which will prevent lanosterol from being converted into ergosterol.
❌ Choice A: Tubulin. This refers to microtubules, which are inhibited by the Griseovulin drugs. It is also inhibited by other non-antifungal drugs like Colchicine, Taxnes, and Vinca alkaloids (Vincristine, vinblastine).
❌ Choice B: RNA synthesis. This is inhibited by the drug flucytosine, which is converted into 5-fluorouracil by the enzyme cytosine deaminase --> incorporated into fungal RNA → inhibits RNA and DNA synthesis -->which inhibits RNA synthesis. Please note, it is not exclusively RNA synthesis; it also inhibits thymidylate synthase, impairing DNA synthesis.
❌ Choice C: Epoxidase. This is inhibited by the drug terbinafine. The use of oral terbinafine is for onychomycosis, and the use of topical tinea pedis. The enzyme squalene epoxidase, which converts Squalene into Squalene Epoxide.
❌ Choice E: Carbohydrates. This is inhibited by the caspofugin. Caspofungin is an echinocandin that inhibits B-1-3-glucan synthase, preventing synthesis of glucan (a key carbohydrate polymer of the fungal cell wall).
