Voriconazole is preferred over fluconazole for invasive Aspergillus infections because:

• A Voriconazole inhibits both CYP51 (lanosterol 14-alpha-demethylase) and beta-glucan synthase, providing dual-target activity against Aspergillus
• B Aspergillus species have intrinsic resistance to fluconazole due to CYP51 mutations, whereas voriconazole (a triazole with extended spectrum) achieves adequate CYP51 inhibition against Aspergillus and moulds ✓
• C Voriconazole penetrates fungal biofilms via its lipophilic amine side chain, which is absent in fluconazole
• D Voriconazole is an echinocandin that targets beta-glucan synthesis, whereas fluconazole only targets ergosterol synthesis

Explanation

Aspergillus species possess intrinsic resistance to fluconazole because their CYP51 enzyme has structural differences that reduce fluconazole binding affinity. Voriconazole has a broader triazole spectrum (additional methyl group at C6 and fluoropyrimidine substitution) that achieves effective CYP51 inhibition in Aspergillus and other moulds including Fusarium. Both fluconazole and voriconazole are azoles (CYP51 inhibitors); echinocandins are the beta-glucan synthase inhibitors.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.