Newer antifungal agents

Advances in pediatric antimicrobial agents development

PURPOSE OF REVIEW

Rising rates of multidrug-resistant organisms has necessitated the development of novel antimicrobials. In this review, we will highlight agents that have recently received licensure and those that are in clinical development.

RECENT FINDINGS

In recent years, development of novel antimicrobial agents has accelerated. Although most studies have targeted the adult population, studies in pediatric patients are underway. Adequately powered clinical trials are needed to establish the safety and role of these new drugs.

SUMMARY

The recent development of novel antimicrobials to combat multidrug-resistant organisms is encouraging; however, more studies in the pediatric population are needed.

Isavuconazole

Objective: To review the pharmacology, chemistry, in vitro susceptibility, pharmacokinetics, clinical efficacy, safety, tolerability, dosage, and administration of isavuconazole, a triazole antifungal agent. Data Sources: Studies and reviews were identified through an English language MEDLINE search (1978 to March 2015) and from http://www.clinicaltrials.gov , Food and Drug Administration (FDA) briefing documents, program abstracts from international symposia, and the manufacturer’s Web site. Study Selection and Data Extraction: All published and unpublished trials, abstracts, in vitro and preclinical studies, and FDA briefing documents were reviewed. Data Synthesis: Isavuconazole has activity against a number of clinically important yeasts and molds, including Candida spp, Aspergillus spp, Cryptococcus neoformans, and Trichosporon spp and variable activity against the Mucorales. Isavuconazole, available for both oral and intravenous administration, is characterized by slow elimination allowing once-daily dosing, extensive tissue distribution, and high (>99%) protein binding. The most commonly reported adverse events, which are mild and limited in nature, include nausea, diarrhea, and elevated liver function tests. Its drug interaction potential appears to be similar to other azole antifungals but less than those observed with voriconazole. Comparative trials are under way or have been recently completed for the treatment of candidemia, invasive candidiasis and aspergillosis, and rare mold infections. Conclusions: Isavuconazole has a broad spectrum of activity and favorable pharmacokinetic properties, providing an advantage over other currently available broad-spectrum azole antifungals and a clinically useful alternative to voriconazole for the treatment of invasive aspergillosis. It may also prove useful for the treatment of candidemia and invasive mold infections; however, these indications await the results of clinical trials.

Pharmacokinetics and pharmacodynamics of antifungals in children and their clinical implications

Invasive fungal infections are a significant cause of morbidity and mortality in children. Successful management of these systemic infections requires identification of the causative pathogen, appropriate antifungal selection, and optimisation of its pharmacokinetic and pharmacodynamic properties to maximise its antifungal activity and minimise toxicity and the emergence of resistance. This review highlights salient scientific advancements in paediatric antifungal pharmacotherapies and focuses on pharmacokinetic and pharmacodynamic studies that underpin current clinical decision making. Four classes of drugs are widely used in the treatment of invasive fungal infections in children, including the polyenes, triazoles, pyrimidine analogues and echinocandins. Several lipidic formulations of the polyene amphotericin B have substantially reduced the toxicity associated with the traditional amphotericin B formulation. Monotherapy with the pyrimidine analogue flucytosine rapidly promotes the emergence of resistance and cannot be recommended. However, when used in combination with other antifungal agents, therapeutic drug monitoring of flucytosine has been shown to reduce high peak flucytosine concentrations, which are strongly associated with toxicity. The triazoles feature large inter-individual pharmacokinetic variability, although this pattern is less pronounced with fluconazole. In clinical trials, posaconazole was associated with fewer adverse effects than other members of the triazole family, though both posaconazole and itraconazole display erratic absorption that is influenced by gastric pH and the gastric emptying rate. Limited data suggest that the clinical response to therapy may be improved with higher plasma posaconazole and itraconazole concentrations. For voriconazole, pharmacokinetic studies among children have revealed that children require twice the recommended adult dose to achieve comparable blood concentrations. Voriconazole clearance is also affected by the cytochrome P450 (CYP) 2C19 genotype and hepatic impairment. Therapeutic drug monitoring is recommended as voriconazole pharmacokinetics are highly variable and small dose increases can result in marked changes in plasma concentrations. For the echinocandins, the primary source of pharmacokinetic variability stems from an age-dependent decrease in clearance with increasing age. Consequently, young children require larger doses per kilogram of body weight than older children and adults. Routine therapeutic drug monitoring for the echinocandins is not recommended. The effectiveness of many systemic antifungal agents has been correlated with pharmacodynamic targets in in vitro and in murine models of invasive candidiasis and aspergillosis. Further study is needed to translate these findings into optimal dosing regimens for children and to understand how these agents interact when multiple antifungal agents are used in combination.