Comparing adsorption of gentamicin by polyacrylonitrile and polyamide hemofiltration filter in an in vitro continuous venovenous hemofiltration model

Introduction

As a high proportion of patients who require continuous renal replacement therapy will also be receiving antibiotics, the issue of whether significant amounts of antibiotic are adsorbed by the haemofilter is relevant to critically ill patients. The aim of the study is to determine the time course of adsorption of gentamicin to a polyacrylonitrile filter (PAN) and a polyamide filter, respectively.

Methods

A unit of expired whole blood was mixed with heparinized lactated Ringer's solution to made up a total volume of 1,000 ml. Five hundred milliliters of this blood–crystalloid mixture was taken to a glass chamber where it was agitated and heated. After the equilibration period, 20% of a standard dose of the drug was infused into the mixing chamber. The blood–crystalloid mixture was then circulated through an in vitro continuous venovenous hemofiltration model. The ultrafiltrate was returned to the mixing chamber and no replacement fluid was infused. As a result, any decrease in drug concentration could only occur due to adsorption. Samples were taken from the mixing chamber for measurement of the drug concentration. At 90 minutes, the remaining 500 ml blood–crystalloid mixture will then be added to the mixing chamber. Samples were taken again after another hour. If the fall in drug concentration was less than those predicted from the dilution effect following the increase in blood–crystalloid volume, it indicates reversibility of adsorption. A second dose of drug was then added and samples were taken afterwards. Adsorption of antibiotic before and after the second dose was compared. Two types of filter, namely a 0.6 m² PAN hemofilter (Multiflow 100; Hospal) and a 0.6 m² polyamide hemofilter (Hemofilter 6S; Gambro), were used in the study and four batches of tests were repeated for each hemofilter.

Results

Drug adsorption by PAN hemofilters was significant, whereas drug adsorption by polyamide hemofilters was much lower compared with that of PAN hemofilters. Gentamicin adsorption by PAN hemofilters was completed at 30 minutes and it was irreversible.

Conclusion

The adsorption properties of gentamicin by the two hemofilters were markedly different.