title: Rapid, simple bioassay for 5-fluorocytosine in the presence of amphotericin B.
abstract: It is important that serum levels of 5-fluorocytosine (5FC) be measured to insure therapeutic levels while avoiding toxicity. This is particularly true in patients with renal insufficiency. The concurrent use of amphotericin B and 5FC complicates the measurement of 5FC in the serum, since fungi used in conventional bioassay systems are uniformly susceptible to amphotericin B. This paper describes the development of a simple, reliable, 6-h bioassay for 5FC in the presence of amphotericin B. The assay is based upon the fact that 5FC diffuses readily through yeast nitrogen base agar, whereas amphotericin B apparently does not. This assay allows rapid adjustments in therapy of patients receiving both 5FC and amphotericin B and has permitted us to maintain 5FC serum levels between limits of 25 and 120 mug/ml in patients with altered renal function.
mesh_terms: D000666:Amphotericin B / Q000032:analysis* / Q000494:pharmacology; D001681:Biological Assay; D002176:Candida albicans / Q000187:drug effects; D003596:Cytosine / Q000031:analogs & derivatives*; D005437:Flucytosine / Q000032:analysis* / Q000494:pharmacology; D008722:Methods
chemical_list: D000666:Amphotericin B; D003596:Cytosine; D005437:Flucytosine