BACKGROUND: The purpose of this study was to investigate the pharmacokinetics of amikacin in critically ill patients undergoing continuous venovenous hemodiafiltration (CVVHDF). METHODS: Pharmacokinetic parameters in each of six renal failure patients were estimated by measurement of amikacin levels in serum and effluent samples. RESULTS: Average clearance of amikacin by CV VHDF was 28.5+/-4.6 mL/min (mean+/-standard deviation). The sieving coefficient was 0.62+/-0.2 in the hemodiafiltration system of Gambro AN69 membrane set. Volume of distribution of amikacin was estimated to be 0.47+/-0.08 L/kg lean body weight. The half-life of amikacin was significantly reduced by hemodiafiltration to 11.4+/-1.6 hr. 40% of the administered amikacin was removed by CVVHDF over the 24 hour study period. CONCLUSION: We recommend that 10 mg/kg of amikacin should be given i.v. every 48 hours to critically ill patients during CVVHDF. However, individualized approach based on therapeutic drug monitoring of plasma amikacin concentration is necessary for optimum amikacin therapy during CVVHDF due to the varying nature of critically ill patients.