Determination of serum 5-fluorocytosine concentrations in the presence of ketoconazole.

Because in-vitro antifungal synergism has been shown between the imidazoles and 5-fluorocytosine, we have evaluated the accuracy of a standard disc diffusion assay for serum 5-fluorocytosine levels in the presence of ketoconazole. In the usual clinical concentrations, ketoconazole does not interfere with the determination of serum 5-fluorocytosine levels by this standard test.