MEMBRANE FILTRATION OF PHARMACEUTICAL SOLUTIONS

The principles and uses of membrane filtration in the preparation of p harmaceutical solutions are discussed. The preparation of pharmaceutic al solutions often requires their passage through a thin polymeric mem brane containing many tiny pores. The purpose is to remove viable and nonviable particles in order to clarify or sterilize the solution. Par ticles may be retained by sieving, entrapment, or electrostatic attrac tion. The largest pore size that will yield a sterile filtrate is 0.2 mum. Membrane filters are either hydrophobic or hydrophilic. The rate of flow through a filter is affected by the resistance of the filter, the viscosity of the solution, and pressure. Filters are commonly comp osed of mixed esters of cellulose, polysulfone, polyvinylidene difluor ide, nylon 66, polycarbonate, or polytetrafluoroethylene. In selecting a membrane filter, a pharmacist must consider pore size, compatibilit y, fluid volume, particulate load, and the filter holder. Various test s are available to evaluate the integrity of filters. Filters are usef ul in testing end products for sterility. The use of an in-line filter during the administration of large-volume injectable solutions can pr event the introduction of particles, air, and microorganisms into the patient. Therapies in which a 0.2-mum filter may be contraindicated in clude lipid emulsions, low-dose infusions, low-volume infusions, drugs for which the pharmacologic properties are altered by the membrane fi lter, and drugs that adhere to the membrane. Pharmacists need an indep th understanding of the principles of filtration, the characteristics of filters, and their use in the filtration of pharmaceutical solution s.