Absence of fungistatic antagonism between flucytosine and cytarabine in vitro and in vivo.

Determination of the MIC of flucytosine for 16 wild isolates of Cryptococcus neoformans and Candida spp. in YNBG medium containing 10 mg/l cytosine demonstrated antagonism of fungistatic activity compared with that determined in YNBG alone. Determination of the MIC in YNBG containing 10 mg/l cytarabine showed no change in activity for 14 of the strains, an increase for one and a decrease for another. Determination of serum flucytosine concentrations in a patient receiving cytarabine simultaneously revealed therapeutic levels. Fluctuations in serum flucytosine concentrations were observed in samples taken before, during and after concurrent cytarabine therapy but these may have resulted from unstable renal function rather than in-vivo inactivation of flucytosine by cytarabine. These data do not support significant antagonism of the fungistatic activity of flucytosine by cytarabine.