University of Arkansas, Fayetteville
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Abstract

An artificial kidney process based on ultrafiltration (called hemodiafiltration) more effectively removes blood toxins, particularly those of higher molecular weight, than conventional dialysis. In hemodiafiltration, replacement liquid must be added directly to the patient's blood to replace liquid filtered out of the blood in the ultrafiltration cartridge. This replacement liquid is made up of' "water for injection" (WFI) and other components such as salts and glucose. WFI is produced either by distillation or reverse osmosis and has a cost of $1.00 per liter. A patient with kidney problems would require three hemodiafiltration treatments per week, each requiring 70-80 liters of WFI. Since the target cost of a treatment is less than $100, the cost of WFI alone, $70- $80, makes the process not economically feasible. In order for the hemodiafiltration process to be widely used and to be affordable in third world countries, a system that produces WFI at a low cost is needed. A process to replace distillation or reverse osmosis must be capable of removing pyrogens. Some information is available in the literature indicating that ultrafiltration membranes can remove endotoxins, the main constituent of pyrogens; however, no studies have been done to establish the type of ultrafiltration membrane that gives optimal removal of endotoxins. Ultrafiltration is known to be a much less expensive process than distillation or reverse osmosis. It is thoroughly estimated that WFI produced by Ultrafiltration System would cost only 25 cents per liter. The purpose of this experimental work is to determine the type of ultrafiltration membrane that effectively removes endotoxins with an efficient flow rate. Regenerated cellulose and polyethersulfone membranes with various molecular-weight-cut-offs were evaluated to determine the endotoxin rejection and flux rates of the membranes. A stirred cell experiment was performed as a short-term test, using disc membranes with a diameter of 76 mm and three types of feed solutions. The Limulus Amebocyte Lysate (LAL) Gel Clot test was performed to measure the concentration of pyrogen in the filtrates. The best candidate from the stirred cell experiment was tested in a Hollow Fiber Cartridge Ultrafiltration System over a longer time period. The results showed that a polyethersulfone membrane with a molecular-weight-cut-off (MWCO) of 10,000 rejected endotoxin to below the US Pharmacopeia ( USP) limit of endotoxin content, 0.25 EU/ml, with the best flux rate. Since polyethersulfone membranes were not available in a cartridge form, the membrane with the closest molecular structure, a polysulfone membrane, was tested in a Hollow Fiber Cartridge Ultrafiltration System. The results showed that the polysulfone membrane cartridge rejected endotoxin content from 625 EU/ml to less than 0.25 EU/ml consistently over a week-long test period. In addition, the flux rate remained constant at 129 L/m2 /hr. Thus, the polysulfone membrane of 10,000 MWCO can be used in an ultrafiltration system to produce Water for Injection (WFI).

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