Rapid enzymatic method for measurement of serum flucytosine levels

Creatinine iminohydrolase (EC 3.5.4.21) quantitatively releases ammonia from flucytosine (5FC) as well as from creatinine. Using 39 sera from eight patients receiving the combination of amphotericin B with 5FC, we demonstrated that this rapid enzymatic reaction provides a valid measure of 5FC levels. The correlation coefficients (r), comparing this method with 5FC bioassay and high-pressure liquid chromatography measurements, were 0.78 and 0.87, respectively. This technique offers a precise alternative to the currently employed methods of measuring 5FC levels. In contrast to other methods, this enzymatic technique is rapid, simple, inexpensive, and has the potential for widespread availability.