Evaluating the Use of Lower Dose Flucytosine for the Treatment of Cryptococcal Meningitis: A Clinical Trial

Background Cryptococcosis is a leading cause of death among people living with HIV. Guidelines recommend combination therapy with amphotericin B and flucytosine, but standard flucytosine dosing of 100 mg/kg/day is associated with hematologic toxicity. The FLOOR trial investigated whether lower flucytosine dosing maintained therapeutic efficacy and reduced toxicity. Methods This phase II, single-arm, open-label trial enrolled 48 adults with HIV and confirmed cryptococcal meningitis at two hospitals in Uganda. Participants received 10 days of flucytosine at 60 mg/kg/day in three divided doses, combined with liposomal amphotericin B (10 mg/kg, single dose) and fluconazole 1200 mg/day for 14 days, followed by standard consolidation therapy. The primary endpoint was the early fungicidal activity (EFA), which measures the rate of Cryptococcus clearance in the cerebrospinal fluid (CSF) in the first 14 days of therapy. Secondary endpoints included CSF sterility at 2 weeks, 18-week survival, and adverse events. Results The EFA of reduced dose flucytosine was 0.28 log10 CFU/mL/day (95% CI, 0.20 to 0.35), which was lower than historical controls in Uganda receiving flucytosine at 100 mg/kg/day of 0.41 log10 CFU/mL/day (P=0.019). At 18-weeks, the estimated survival probability was 77% (95% CI, 66% to 90%). The incidence of rehospitalization (25%) and culture-positive relapse (6.3%) were higher than expected. Grade 3–4 hematologic toxicity was similar (10% leukopenia; 21% anemia) to historical incidence. Conclusions Reduced flucytosine dose of 60 mg/kg/day for 10 days demonstrated inferior efficacy in CSF fungal clearance. These findings support further investigation of dose optimization strategies. Trial Registration ClinicalTrials.gov: NCT06414512