voriconazole + posaconazole

Voriconazole and posaconazole are second-generation triazole antifungal agents with broad-spectrum activity against fungal pathogens. They work by inhibiting fungal cytochrome P450-dependent enzyme 14α-demethylase (CYP51), which disrupts ergosterol synthesis in fungal cell membranes. While they share similar mechanisms of action and therapeutic uses, they have distinct pharmacokinetic properties and safety profiles. Key differences include: * **Bioavailability:** Voriconazole (>95%) is higher and less variable than posaconazole (variable, dependent on dosage and food intake). * **Protein Binding:** Voriconazole (58%) is less protein-bound than posaconazole (>98%). * **Metabolism:** Voriconazole is primarily metabolized hepatically via CYP enzymes (CYP2C19, 2C9, 3A4), while posaconazole is primarily metabolized via glucuronidation. * **Half-life:** Posaconazole has a significantly longer half-life (15-35 hours) compared to voriconazole (6-24 hours). * **Elimination:** Voriconazole is primarily eliminated hepatically with minimal renal excretion of unchanged drug, while posaconazole is primarily excreted unchanged in feces. Both drugs are effective against *Candida* species, *Aspergillus* species, and *Cryptococcus neoformans*. Posaconazole has additional activity against Mucorales (zygomycetes), which voriconazole lacks. Posaconazole is generally considered better tolerated with fewer CNS side effects, visual disturbances, and phototoxic reactions compared to voriconazole. Voriconazole has the advantage of higher bioavailability and a faster onset of action.