Effect of drug concentration on adsorption of levofloxacin by polyacrylonitrile haemofilters

We studied an in vitro model of continuous venovenous haemofiltration to determine levofloxacin adsorption by polyacrylonitrile (PAN) filters. Four doses of levofloxacin (5, 25, 50 and 100 mg) were used, resulting in circulating concentrations of levofloxacin at 120 min of 3.56 ± 0.14, 15.84 ± 2.08, 31.42 ± 1.95 and 58.23 ± 1.10 mg/L, respectively. Adsorption at 2 h was 0.65 ± 0.17, 5.99 ± 2.49, 12.30 ± 2.34 and 30.13 ± 1.32 mg, respectively (P < 0.001). From 2 h to 4 h, increasing the blood pump rate and the ultrafiltration rate had no effect on adsorption. When the concentration was decreased from 3.55 ± 0.13 mg/L at 4 h to 2.16 ± 0.11 mg/L at 5 h by addition of lactated Ringer's solution, adsorption decreased from 0.67 ± 0.16 mg to 0.21 ± 0.25 mg (P < 0.05). These data show that adsorption of levofloxacin by PAN haemofilters is concentration dependent and reversible in vitro and suggest that adsorption by haemofilters is unlikely to affect levofloxacin pharmacokinetics significantly in vivo.