Pharmacokinetic Studies on the Oral Antimycotic Agent 5-Fluorocytosine in Individuals with Normal and Impaired Kidney Function

Abstract

Pharmacokinetic studies were performed on the systemic antimycotic agent 5-fluorocytosine (5-FC) by giving 2 g orally to 10 healthy adult volunteers and to 40 patients with renal impairment of various degree (serum creatinine concentration varying from 1.0 to 16.4 mg/l00 ml) including 5 nephrectomized or anuric patients. The microbiological method used for the measurement of the serum and urinary concentrations of the drug is described in detail. In 20 patients endogenous creatinine clearance was determined in addition to the serum creatinine concentration. The average biological half-life of 5-FC in serum was 2.89 h in the healthy individuals (range 2.36–3.99 h) but in the patients, it was significantly prolonged with increasing serum creatinine concentration and decreasing creatinine clearance. The average half-life in the five nephrectomized or anuric patients was 85.0 h (29.9–250 h). A linear correlation was found to exist between the elimination rate constant of the drug and creatinine clearance, and based on this, a 5-FC dosage schedule has been proposed for patients with impaired kidney function. 5-FC is eliminated almost exclusively by the kidneys but has no renal toxicity. Provided that dosage is adapted accordingly, the drug is appropriate for chemotherapeutic treatment of patients with renal impairment which is a relative contraindication to amphotericin B.