Rapid determination of 5-fluorocytosine levels in blood

Spurious azotemia associated with 5-fluorocytosine therapy

A patient with false elevation of serum creatinine level due to 5-fluorocytosine (5-FC) is reported. 5-FC interferes with the enzymatic method used for creatinine determination in the Kodak Ektachem analyzer. Clinicians should be aware of the potential for spurious azotemia in patients receiving 5-FC therapy for fungal urinary tract infections.

Performance characteristics of two bioassays and high-performance liquid chromatography for determination of flucytosine in serum

We compared the accuracy and precision of two microbiological methods and one high-pressure liquid chromatography (HPLC) procedure used to measure the concentrations of flucytosine in serum. On the basis of an analysis of six standards, all methods were judged reliable within acceptable limits for clinical use. With the biological methods, a slight loss of linearity was observed in the 75- to 100-micrograms/ml range. Compared with the bioassays, the HPLC method did not present linearity problems and was more precise and accurate in the critical zone of 100 micrograms/ml. On average, results obtained with patient sera containing 50 to 100 micrograms of flucytosine per ml were 10.6% higher with the HPLC method than with the bioassays. Standards for the biological assays may be prepared in serum or water.

Treatment of systemic fungal infections: recent progress and current problems

Systemic mycoses continue to emerge as life-threatening infections. Considerable progress in treating these infections is being achieved through better application of established available antifungal agents (amphotericin B, flucytosine, miconazole and ketoconazole), and through development of promising investigational agents (fluconazole, itraconazole). Systemic fungal infections, however, continue to present major problems, including clinical resistance, microbiological resistance, emergence of new pathogens, and involvement of more immunocompromised patients. The purpose of this paper, therefore, is to review the recent progress and current problems in treatment of systemic fungal infections.

Simplified bioassay method for measurement of flucytosine or ketoconazole

A simple agar-well diffusion bioassay suitable for measurement of flucytosine or ketoconazole was developed by using Candida pseudotropicalis ATCC 46764 as the assay organism. A test medium composed of (per liter) 7 g of Trypticase peptone, 7 g of YNB (yeast-nitrogen base), 15 g of glucose, and 15 g of agar was seeded with an inoculum which had been grown to no. 2 McFarland turbidity after 4 to 6 h in YNB-glucose broth. Determinations of flucytosine or ketoconazole were performed without necessity of heating or diluting of serum samples to alleviate amphotericin B interference. A linear relationship between zone diameters and log10 concentration of the drugs was observed over the pharmacologically relevant ranges of 25 to 160 micrograms/ml for flucytosine and 0.5 to 20 micrograms/ml for ketoconazole. The mean coefficient of variability for samples measured on 5 separate days was 2.4% for flucytosin and 4.0% for ketoconazole. This assay represents a significant improvement over previous bioassay methods in that a single test system may be used for measurement of either flucytosine or ketoconazole, no serum dilution or pretreatment is required, inoculum preparation is accomplished entirely on the day of the assay, and sharp, clearly defined zones of inhibition are obtained with both drugs.