5-fluorocytosine-related bone-marrow depression and conversion to fluorouracil: a pilot study

Diagnosis and management of cryptococcal meningitis in HIV-infected adults

Cryptococcal meningitis is a leading cause of morbidity and mortality globally, especially in people with advanced HIV disease. Cryptococcal meningitis is responsible for nearly 20% of all deaths related to advanced HIV disease, with the burden of disease predominantly experienced by people in resource-limited countries. Major advancements in diagnostics have introduced low-cost, easy-to-use antigen tests with remarkably high sensitivity and specificity. These tests have led to improved diagnostic accuracy and are essential for screening campaigns to reduce the burden of cryptococcosis. In the last 5 years, several high-quality, multisite clinical trials have led to innovations in therapeutics that have allowed for simplified regimens, which are better tolerated and result in less intensive monitoring and management of medication adverse effects. One trial found that a shorter, 7-day course of deoxycholate amphotericin B is as effective as the longer 14-day course and that flucytosine is an essential partner drug for reducing mortality in the acute phase of disease. Single-dose liposomal amphotericin B has also been found to be as effective as a 7-day course of deoxycholate amphotericin B. These findings have allowed for simpler and safer treatment regimens that also reduce the burden on the healthcare system. This review provides a detailed discussion of the latest evidence guiding the clinical management and special circumstances that make cryptococcal meningitis uniquely difficult to treat.

5-Flucytosine Longitudinal Antifungal Susceptibility Testing of Cryptococcus neoformans: A Substudy of the EnACT Trial Testing Oral Amphotericin

Background

The EnACT trial was a phase 2 randomized clinical trial conducted in Uganda, which evaluated a novel orally delivered lipid nanocrystal (LNC) amphotericin B in combination with flucytosine for the treatment of cryptococcal meningitis. When flucytosine (5FC) is used as monotherapy in cryptococcosis, 5FC can induce resistant Cryptococcus mutants. Oral amphotericin B uses a novel drug delivery mechanism, and we assessed whether resistance to 5FC develops during oral LNC-amphotericin B therapy.

Methods

We enrolled Ugandans with HIV diagnosed with cryptococcal meningitis and who were randomized to receive 5FC and either standard intravenous (IV) amphotericin B or oral LNC-amphotericin B. We used broth microdilution to measure the minimum inhibitory concentration (MIC) of the first and last cryptococcal isolates in each participant. Breakpoints are inferred from 5FC in Candida albicans. We measured cerebral spinal fluid (CSF) 5FC concentrations by liquid chromatography and tandem mass spectrometry.

Results

Cryptococcus 5FC MIC50 was 4 µg/mL, and MIC90 was 8 µg/mL. After 2 weeks of therapy, there was no evidence of 5FC resistance developing, defined as a >4-fold change in susceptibility in any Cryptococcus isolate tested. The median CSF 5FC concentration to MIC ratio (interquartile range) was 3.0 (1.7-5.5) µg/mL. There was no association between 5FC/MIC ratio and early fungicidal activity of the quantitative rate of CSF yeast clearance (R2 = 0.004; P = .63).

Conclusions

There is no evidence of baseline resistance to 5FC or incident resistance during combination therapy with oral or IV amphotericin B in Uganda. Oral amphotericin B can safely be used in combination with 5FC.

Antifungal Efficacy of an Intravenous Formulation Containing Monomeric Amphotericin B, 5-Fluorocytosine, and Saline for Sodium Supplementation

PURPOSE

Amphotericin B (AmB) and 5-fluorocytosine (5-FC) exhibit additive to synergistic activity against systemic mycoses. Incompatibility of prescribed formulations precludes concomitant IV administration, a route with distinct advantages. Previously, we used PEG-DSPE micelles to produce a reformulation of Fungizone (AmB-SD), AmB solubilized by sodium deoxycholate, called mAmB-90. Herein, we describe a second reformulation that facilitates co-delivery of mAmB-90 and 5-FC, and evaluate the effect of PEG-DSPE micelles on the combination's activity against Candida albicans.

METHODS

We assessed the effect of 5-FC addition on the stability, in vitro toxicity, and antifungal efficacy of mAmB-90. The aggregation state and particle size of mAmB-90 combined with 5-FC (FmAmB-90) was evaluated over 48 h. Hemolytic activity was measured in vitro. Antifungal activity was determined in vitro against C. albicans. The efficacy of monotherapy and combination treatment was evaluated in a neutropenic mouse model of disseminated candidiasis.

RESULTS

The aggregation state, particle size, and hemolytic activity of mAmB-90 were unaffected by 5-FC. While antifungal activity was similar in vitro, mAmB-90 alone and combined with 5-FC was more potent than AmB-SD in vivo.

CONCLUSIONS

Short-term stability and in vivo efficacy of our formulation suggest potential to simultaneously deliver AmB and 5-FC for potent antifungal efficacy.

The effect of gut microbiota on drug metabolism

INTRODUCTION

Numerous drugs and toxicants must be metabolized to an active form. Metabolic activation by host tissues, such as the liver, has been well studied. However, drug and toxicant metabolism by the intestinal microbiota is an unexplored, but essential, field of study in pharmacology and toxicology. The taxonomic diversity and sheer numbers of the intestinal microbiota, and their capacity to metabolize xenobiotics, underscore the importance of this mode of metabolism.

AREAS COVERED

Metabolism by the intestinal microbiota has focused on the natural products of glycosides hydrolyzed by intestinal microbiota enzymes, but not by host tissues. Metabolism of synthetic drugs by the intestinal microbiota has been less-intensively investigated. This review provides an overview of xenobiotic metabolism by the intestinal microbiota of both natural products and synthetic drugs.

EXPERT OPINION

Metabolism by the intestinal microbiota might result in a different metabolite profile than that produced by host tissues. This could potentially result in either activation or inactivation of the pharmacological and/or toxicological actions of the compound in question. The contribution of the intestinal microbiota to drug metabolism remains relatively unexplored. Therefore, studies of xenobiotic metabolism by the intestinal microbiota need to be included in new drug development as well as classical studies of host tissue metabolism.

Defining targets for investigating the pharmacogenomics of adverse drug reactions to antifungal agents

Adverse drug reactions (ADRs) associated with antifungal therapy are major problems in patients with invasive fungal infections. Whether by clinical history or patterns of genetic variation, the identification of patients at risk for ADRs should result in improved outcomes while minimizing deleterious side effects. A major contributing factor to ADRs with antifungal agents relates to drug distribution, metabolism and excretion. Genetic variation in key genes can alter the structure and expression of genes and gene products (e.g., proteins). Thus far, the effort has focused on identifying polymorphisms with either empirical or predicted in silico functional consequences; the best candidate genes encode phase I and II drug-metabolizing enzymes (e.g., CYP2C19 and N-acetyltransferase), plasma proteins (albumin and lipoproteins) and drug transporters (P-glycoprotein and multidrug resistance proteins), which can affect the disposition of antifungal agents, eventually leading to dose-dependent (type A) toxicity. Less is known regarding the key genes that interact with antifungal agents, resulting in idiosyncratic (type B) ADRs. The possible role of certain gene products and genetic polymorphisms in the toxicities of antifungal agents are discussed in this review. The preliminary data address the following: low-density lipoproteins and cholesteryl ester transfer protein in amphotericin B renal toxicity; toll-like receptor 1 and 2 in amphotericin B infusion-related ADRs; phosphodiesterase 6 in voriconazole visual adverse events; flavin-containing monooxygenase, glutathione transferases and multidrug resistance proteins 1 and 2 in ketoconazole and terbinafine hepatotoxicity; CYP enzymes and P-glycoprotein in drug interactions between azoles and coadministered medications; multidrug resistance proteins 8 and 9 on 5-flucytosine bone marrow toxicity; and mast cell activation in caspofungin histamine release. This will focus on high-priority candidate genes, which could provide a starting point for molecular studies to elucidate the potential mechanisms for understanding toxicity associated with antifungal drugs as well as identifying candidate genes for large population prospective genetic association studies.