Triazole Antifungal Agents in Invasive Fungal Infections: a Comparative Review

Invasive fungal disease continues to be a problem associated with significant morbidity and high mortality in immunocompromised and, to a lesser extent, immunocompetent individuals. Triazole antifungals have emerged as front-line drugs for the treatment and prophylaxis of many systemic mycoses. Fluconazole plays an excellent role in prophylaxis, empirical therapy, and the treatment of both superficial and invasive yeast fungal infections. Voriconazole is strongly recommended for pulmonary invasive aspergillosis. Posaconazole shows a very wide spectrum of activity and its primary clinical indications are as salvage therapy for patients with invasive aspergillosis and prophylaxis for patients with neutropenia and haematopoietic stem-cell transplant recipients. Itraconazole also has a role in the treatment of fungal skin and nail infections as well as dematiaceous fungi and endemic mycoses. Fluconazole and voriconazole are well absorbed and exhibit high oral bioavailability, whereas the oral bioavailability of itraconazole and posaconazole is lower and more variable. Posaconazole absorption depends on administration with a high-fat meal or nutritional supplements. Itraconazole and voriconazole undergo extensive hepatic metabolism involving the cytochrome P450 system. The therapeutic window for triazoles is narrow, and inattention to their pharmacokinetic properties can lead to drug levels too low for efficacy or too high for good tolerability or safety. This makes these agents prime candidates for therapeutic drug monitoring (TDM). Target drug concentrations for voriconazole and itraconazole should be >1 μg/mL and for posaconazole >1.5 μg/mL for treatment. Blood should be drawn once the patient reaches steady state, which occurs after 5 and 7 days of triazole therapy. Routine TDM of fluconazole is not required given its highly favourable pharmacokinetic profile and wide therapeutic index. The aim of this review is to provide a brief update on the pharmacology, activity, clinical efficacy, safety and cost of triazole agents (itraconazole, fluconazole, voriconazole and posaconazole) and highlight the clinical implications of similarities and differences.