5-Fluorocytosine kinetics in patients with acute renal failure undergoing continuous hemofiltration.

The pharmacokinetic disposition of 5-fluorocytosine (5-FC) was studied in 7 patients with acute renal failure undergoing continuous hemofiltration (CH). CH was performed with a high-flux membrane and the average filtration rate (FR) was 16.3 ml/min. Following an intravenous loading dose of 2,500 mg, 5-FC concentrations were measured in plasma and ultrafiltrate. The half-lives of 5-FC were markedly prolonged in all patients, ranging from 15.9 to 37.2 h and longer half-lives corresponded to lower FR. The clearance of 5-FC averaged 97.5% of the FR. Within 48 h, 29-35% of the administered dose was recovered in the ultrafiltrate of 3 patients. The volume of distribution ranged from 0.772 to 0.982 l/kg. We found a linear relationship between the elimination rate constant and the FR, and based on these data, a dosage schedule is proposed regarding the use of 5-FC in patients treated with CH.