Flucytosine (5-fluorocytosine) is an antifungal used in combination with amphotericin B for cryptococcal meningitis. Its mechanism of action involves intracellular conversion to 5-fluorouracil, which then:

• A Inhibits ergosterol synthesis by blocking lanosterol demethylase
• B Binds to ergosterol and forms membrane pores
• C Inhibits thymidylate synthase, disrupting DNA and RNA synthesis ✓
• D Inhibits beta-1,3-glucan synthase, disrupting cell wall synthesis

Explanation

Flucytosine enters fungal cells via cytosine permease and is deaminated to 5-fluorouracil (5-FU). 5-FU is then converted to 5-FdUMP, which inhibits thymidylate synthase, blocking thymidine and DNA synthesis. Human cells lack efficient cytosine deaminase conversion, contributing to selective toxicity. Lanosterol demethylase is the azole target. Ergosterol binding is amphotericin B. Beta-1,3-glucan synthase is the echinocandin target.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.