[Monitoring of treatment involving 5-fluorocytosine]

The occurrence of hematologic and neurologic complications probably caused by an overdose of 5-FC has prompted us to study 5-FC pharmacokinetics in 10 patients under a 5-FC and amphotericin B. On the basis of our findings we have determined the optimal dosage that achieves desired concentrations. In 5 cases this dosages was found to differ from that suggested by the manufacturer. 5-FC concentrations were however higher than predicted levels as a result of the association with amphotericin B. A subsequent modification of dosage was needed in 10 patients. 5 undesirable side effects were recorded: thrombopenia (1 case), neutropenia (1 case), diarrhea (2 cases), and isolated rise in transaminases. In 4 patients with high 5-FC concentrations, chromatograms showed a peak possibly formed by 5-FU, suggesting that 5-FC may be converted into 5-FU.