Pharmacokinetics of amphotericin B and flucytosine

The absorption of flucytosine from the digestive tract is very good but minimal with amphotericin B. For this reason, amphotericin B has to be injected intravenously. Fungistatic levels are achieved rapidly with flucytosine and slowly with amphotericin B, since the dose has to be increased slowly. Distribution of flucytosine in other body fluids is high, whereas with amphotericin B it is poor. Flucytosine is excreted mainly via the kidney without metabolism, whereas amphotericin B is eliminated mainly by metabolism. Therefore, amphotericin B dosage does not have to be adapted to kidney function, which is the case for flucytosine. The half-life of flucytosine is short (hours), that of amphotericin B is long (days); flucytosine is haemodialysable, whereas amphotericin B, probably owing to the high protein binding, is not.