Antifungal combination therapy in localized candidosis

Flucytosine and its clinical usage

Flucytosine is an antifungal agent first licensed in the 1970's. However, its clinical value has long been overlooked and its availability across the globe is limited. This review highlights the important clinical and pharmacological aspects of flucytosine. This a narrative review of the clinical and in vitro susceptibility literature, with a focus on clinical uses for flucytosine. Detailed literature review including early literature related to primary and acquired resistance to flucytosine. Flucytosine has good antifungal activity against Cryptococcus species, Candida species, and dematiaceous fungi. Its water solubility enables good penetration into the eye, urinary tract, central nervous system (CNS), cardiac vegetations and fungal biofilms. In combination with amphotericin B, it shows early fungicidal activity against Cryptococcus species, and this translates to ~20% improved survival in cryptococcal meningitis. Combination therapy also reduces the mortality of Candida meningitis, and should be used in neonatal candidiasis because of the high frequency of CNS infection. Monotherapy for urinary candidiasis is under-studied, but is usually effective. It is probably valuable in the treatment of Candida endocarditis and endophthalmitis: there are few data. It is not effective for aspergillosis or mucormycosis. Flucytosine monotherapy of urinary candidiasis resulted in 22% developing resistance on therapy and failing therapy, and in 29% of 21 patients with cryptococcosis. Certain regions of the world still do not have access to flucytosine compromising the management of certain severe fungal infections. Flucytosine has an important role in combination therapy for yeast and dematiaceous infections and probably as monotherapy for urinary candidiasis, with a modest risk of resistance emergence. Facilitating access to flucytosine in those regions (especially low-income countries) might alleviate the mortality of invasive fungal diseases.

Combination antifungal therapy: the new frontier

The past decade has seen a significant increase in the incidence of invasive fungal infections. The antifungal armamentarium for the treatment of serious fungal infections remains limited. A possible approach to overcoming antifungal drug resistance and high mortality rates seen in severe fungal infections is to combine two or three classes of antifungals, especially if the drugs have different mechanisms of action. Combinations of new agents along with more traditional antifungals have now been shown to possess some synergistic or at least additive activity against many fungi in in vitro and animal studies. On the other hand, caution is still needed since some antifungal combinations have also demonstrated antagonistic activity. Well-controlled clinical trials are still required to define the most efficacious antifungal regimen. Furthermore, these trials should also evaluate the side-effect potential of combination regimens and the pharmacoeconomic impact these regimens may have.

Combination antifungal therapy againstCandidaspecies: the new frontier-are we there yet?

In the past decade, we have seen a significant increase in the incidence of invasive fungal infections. In addition, opportunistic fungal infections resistant to antifungal agents have become increasingly common and their frequency will more than likely continue to increase. The antifungal armamentarium for the treatment of serious fungal infections remains limited. A possible approach to overcoming antifungal drug resistance and high mortality rates seen in severe fungal infections is to combine two or three classes of antifungals, especially if the drugs have different mechanisms of action. The unique properties of newer antifungals now provide us with the opportunity to investigate antifungal combinations that may become the standard of care for serious fungal infections. Combinations of new agents along with more traditional antifungals have now been shown to possess some synergistic or at least additive activity against Candida in clinical trials. On the other hand, caution is still needed since other antifungal combinations have demonstrated antagonistic activity in vitro. Well-controlled clinical trials are needed to define the most efficacious antifungal regimen. Furthermore, these trials should also evaluate the side effect potential of combination regimens and the pharmacoeconomic impact these regimens may have. Thus, while much optimism exists for combination therapy, there is much yet to be done.

Rationale for combination antifungal therapy

The relentless increase of invasive fungal infections and poor outcomes associated with available antifungal agents prompted the search for better therapeutic strategies. Combining antifungal drugs was recommended as a means to enhance efficacy in a variety of invasive infections including cryptococcosis, candidiasis, and aspergillosis. With the exception of cryptococcal meningitis, data from controlled clinical trials supporting such combinations are sparse. Moreover, little consensus exists regarding which combinations are synergistic or antagonistic in vitro and in vivo. Based on available data, several principles underlie these combinations.