Gentamicin clearance during continuous arteriovenous hemodiafiltration

Objective: To investigate the feasibility of predicting gentamicin dosing requirements during continuous arteriovenous hemodiafiltration (CAVHD). Design: Prospective study. Setting: General intensive therapy unit in a university teaching hospital. Patients: Five adult patients with acute renal failure in whom both dialytic and gentamicin therapy were indicated. Measurements and Main Results: CAVHD clearance and total body clearance of gentamicin were estimated from serial gentamicin concentrations in the blood and the combined ultrafiltrate and dialysate. Results (mean ± SD) were: CAVHD clearance of gentamicin 5.2 ± 1.8 mL/min; total body clearance of gentamicin 20.5 ± 6.9 mL/min; ultrafiltrate flow rate 7.0 ± 2.4 mL/min (420 ± 146 mL/hr). CAVHD clearance of gentamicin was small and represented approximately 25% of total body clearance of gentamicin, although significant interpatient variation existed in these measurements and in the proportion of total gentamicin clearance attributable to CAVHD. CAVHD clearance of gentamicin was related to the ultrafiltrate flow rate (r² = .81). Conclusions: CAVHD clearance of gentamicin may be predicted for variable ultrafiltrate flow rates. However, due to its minor and variable contribution to total body clearance of gentamicin, prediction of gentamicin dosing requirements based on estimates of CAVHD clearance of gentamicin would be precluded and close monitoring of circulating gentamicin concentrations during CAVHD is necessary.