Liquid purification or separation – Filter – Material
Reexamination Certificate
2002-03-14
2004-06-08
Walker, W. L. (Department: 1723)
Liquid purification or separation
Filter
Material
C210S660000, C210S668000, C210S669000, C210S663000, C210S753000, C210S650000, C210S651000, C252S186340, C252S187200
Reexamination Certificate
active
06745903
ABSTRACT:
BACKGROUND OF THE INVENTION
General Background and State of the Art
This invention is directed to methods for the on-line, on-demand preparation of sterile, water-for-injection grade water and water preparations produced by such methods.
In the first decades of artificial kidney treatment, technical efforts focused on developing effective dialysis membranes, machines and water systems. In the 1970s, some articles discussing the importance of pyrogenic reactions during hemodialysis induced installation of reverse osmosis systems for preparation of more pure dialysis fluid. In the last decade, growing knowledge of the function of endothelial cells and their role in disease has helped to understand the possible alterations in endothelial cell structure and function evoked by uremia and its dialytic therapy.
Factors injuring the vascular endothelium during hemodialysis include complement activation due to membrane contact, bacterial endotoxins, endotoxin containing immunocomplexes, hyperlipidemia, and cell adhesions. The activated monocytes migrate through endothelial intracellular junctions becoming macrophages; the filtered LDL particles transform them into foam cells. Bacterial endotoxin activates monocytes and the other white blood cells, increasing the chance for endothelial cell injury, arteriosclerosis and inflammatory problems such as amyloidosis.
Many studies emphasize the importance of endotoxin-free dialysate and conclude that finding of transmembrane passage of low molecular weight intact species of LPS that are found in clinically used dialysates emphasizes the importance of obtaining LPS-free dialysates in order to improve the biocompatibility of hemodialysis (for a review, see Lonnemann, G. et al., Nephrol. Dial. Transplant. (1996) 11:946-949).
Other types of renal replacement therapies such as CRRT or hemodiafiltration require sterile replacement fluid that must also be apyrogenic. These therapies are supplied with these solutions in a pre-packaged format at a significant cost. This substantially contributes to the inadequate usage of these therapeutic modalities even if they were more desirable from the patient's point of view.
It has been demonstrated that bacterium and endotoxin-free dialysate resulted in reduced activation of monocytes and lower levels of interleukins and tumor necrosis factor in the patient's blood. Therefore, it is expected that regular use of sterile and endotoxin-free dialysate will help decrease the cardiovascular morbidity and mortality rate of patients undergoing hemodialysis. Since more than 50 percent of the patient population undergoing dialysis treatment is less than 65 years old, preserving their ability to work is very important. Procedures helping to slow the progression of cardiovascular diseases in patients undergoing hemodialysis will help decrease the cost of treatment and may improve the success of renal transplantation.
There is a need to develop a new technology for producing ultrapure, sterile water (preferably of water-for-injection quality) for kidney replacement therapy without significantly affecting the cost of dialysis treatment. The source water for dialysis is potable water. Even after treatment by the water companies, potable water, although safe to drink, contains low levels of mineral salts, trace metals, organic compounds, dissolved gases and colloidal matter, together with particles in suspension and microorganisms. Moreover, unlike other raw materials, water supplies vary widely in quality, both geographically and seasonally.
Before water can be used in the manufacture of pharmaceuticals, it must be purged of its impurities to a degree that is defined by the pharmacopoeias and regulatory authorities like the FDA. The most widely used and accepted method to produce water-for-Injection (WFI) is distillation. The use of distillation makes WFI expensive. The quality of WFI is defined in terms of acceptable limits for inorganic and organic impurities determined by specific physical and chemical tests. WFI must be apyrogenic and free from suspended particles. The FDA recommends that the bacterial count should be below 10 CFU/100 ml. WFI must have a conductivity, measured on-line, less than 1.3 &mgr;S/cm at 25° C. However, the acceptable conductivity range of off-line samples, taking into account pH (which must lie between 5.0 and 7.0), temperature and carbon dioxide equilibrium, is likely to be 2.1 to 4.7 &mgr;S/cm. The maximum acceptable total organic carbon (TOC) level is 500 parts per billion.
The modern approach to purifying water for pharmaceutical applications is to use systems incorporating synergistic combinations of purification technologies. These technologies fall into two broad groups: ion-exchange and membrane processes. The major ion-exchange technique is deionization, using both cation-exchange and anion-exchange resins, while the principal membrane processes are reverse osmosis (RO), ultrafiltration (UF) and microfiltration (MF). The hybrid technology called electrodeionization (EDI) utilizes both ion-selective membranes and ion-exchange resins. These methods are then combined with distillation to produce WFI.
There are prior art methods describing the production of WFI without distillation. Reti and Benn (U.S. Pat. No. 4,610,790) disclosed a method using a plurality of filtration and deionization steps producing sterile water corresponding to USP XX specifications. Klein and Beach (U.S. Pat. No. 4,495,067) disclosed a similar system for making pyrogen-free water. Despite these advances in membrane technology for pyrogen removal, distillation remained the method of choice for WFI. Another invention concerning endotoxin removal from biological fluids was disclosed by Harris (U.S. Pat. No. 3,959,128). He employed non-ionogenic hydrophobic synthetic polymers to adsorb endotoxin from biological fluids.
The literature quoted here points out the complexity of the spectrum of pyrogens present in water and dialysate. The discovery of the heat-stable, low molecular weight pyrogen(s) from Pseudomonas questions the efficacy of ultrafiltration as a tool for pyrogen removal. There is no evidence that the method of Harris would be useful in this regard either.
Renal replacement therapies require high volumes of pure water at a low cost. The high cost of producing large volumes of WFI by the standard technique (distillation) precluded its use in artificial kidney therapies even though it is warranted clinically. It would be desirable to develop a system capable of producing on-line WFI quality water at a low cost from potable water in volumes necessary to meet the needs of dialysis units.
Membrane and particle-based water purification methods are not 100% efficient in eliminating microorganisms. Therefore a high throughput sterilization method is essential to ensure sterility of the purified water product. The sterilizing medium must be in a solid phase in order to minimize contamination of the water to be sterilized as any additive must be removed at the end if the quality criteria for WFI are to be met.
Halogens, such as chlorine and iodine, have demonstrated their utility in destroying microorganism contamination in water. Iodine is more useful in this regard because it can be immobilized to solid phase adsorbents that minimize iodine carryover into the water product. These solid phases are primarily strong anion exchangers. An example is taught by Rajan, U.S. Pat. No. 5,635,063. The iodine released from the adsorbent must subsequently be removed.
One such method is using immobilized silver compounds such as in U.S. Pat. No. 5,635,063 or U.S. Pat. No. 5,366,636. This is an expensive method and may potentially release silver into the water stream, which would be highly undesirable. Another method involves the reduction of iodine with e.g., sulfur dioxide as described in U.S. Pat. No. 5,356,611. The continuous, on-line reduction of iodine by the addition of external reagents would require complicated process controls and equipment. The oxidized form of the added substance must then be removed. This wou
Catalyst Law Group
Farber, Esq. Michael B.
Menon Krishnan S
Walker W. L.
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