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Membrane Filtration
Sterilisation by Membrane Filtration
| Question | Answer |
|---|---|
| What is the principle of membrane filtration? | Reduction of viable/non-viable particles in gases and fluid that cannot be removed by heat & irradiation sterilisation. Principle is to remove organisms from the product and not deactivate. Does not involve killing or inhibiting growth of MO's. |
| How are thermolabile medicaments sterilised? | If an active ingredient cannot be terminally sterilised it can sterilised wth a filtration procedure using a suitable filter. Filter needs to have demonstrated via a microbial challenge test with a suitable test MO, that is a satisfactory filter. |
| How is sterilisation by filtration different to other methods of sterilisation? | Cold and wet, Not as reliable Not terminal sterilisation Thermolabile material must be stable in solution Aseptic Process Multi step process |
| What are the 4 steps in sterilisation by filtration? | 1. Filtration of the solution through a suitable sterile, bacteria retaining filter. 2. Aseptic distribution of the filtered solution into previously sterilised containers with a measurement phase. 3. Aseptic closure of the containers 4. Sterility test |
| What are the key factors for sterilisation by filtration? | Production process + environment designed to minimise MO contamination. Regular monitoring. Equipment, closures, closures and ingredients are sterilised. Filtration process carried out close to filling point. D/stream of FP to prevent recontamination. |
| What is prefiltration and why is it important? | Extends working life of final filters Retains large number of particles, stops premature clogging of final filters Depth filter used for prefiltration Prefilter and final filter should closely match For good flow rate, prefilter area should be larger |
| Explain depth filters | Pads containing compacted polypropylene, cellulose or glass fibres Retention efficiency depends on nominal pore rating and selective adsorption of bacteria to filter Pores larger than particles removed but uneven channels and change of direction traps |
| What determines the size of particles a depth filter retains? | The maximum pore diameter and retention efficiency of the filter determine the size of the particles retained. |
| How is pre-filtration carried out? | Filtration may be carried out under vacuum or positive pressure Uniform pressure is important and should not exceed 35-70 kPa because compression of the mat reduces flow rate Has high dirt holding capacity |
| What are the diadvantages of depth filters? | Lose significant volume Components like proteins can adsorb onto the filter, reducing conc'n Filter fibres may shed, first portion of filtrate may be rejected Penetration of MO depends on the time needed for filtration, can pass through if pressure inc |
| What are screen filters? | Membrane filters with microporous films of specific size ratings. Called screen, sieve, microporous Retain particles larger than their pore size by surface capture |
| In the filtration process, how is the sterilisation process determined? | Sterilisation filter is the filter used closest to the filling point in the final container. |
| What size filter is used for membrane filters? | Pore size not greater than 0.22 microns |
| What are the characteristics of membrane filters? | 125-150 micron in thickness Regularly spaced pores Range from 13-293 mm in diameter Low dirt handling capacity easily clogged by particles just larger than pores size Air locking |
| What are the advantages of membrane filters? | All particles larger than pore size are retained large open volume gives goofd flow rate Volume of liquid retained in membrane is small, can be expelled without breaking sterility Quality of filtrate not altered by adsorption of solutes or foreign part |
| List the types of membrane filters | Hydrophilic (cellulose esters) Surfactant free Low protein binding (used for peptides) Hydrophobic (polytetrafluouroethylene, polyvinyl chloride and polyvinyl difluoride) |
| Explains hydrophobic edge membranes | Hydrophilic filters with a hydrophobic edge. Solution passes through the centre, edge doesn't get wet, doesn't retain the product. Used for sterility testing liquids with antimicrobial agents. |
| What are the advantages of using pre-fabricated membrane filters? | Consistent Conveneient Surfactant free disposable filtration areas bidirectional support inlet luer lock outlet luer slip |
| What is the concept of an integrity test? | To verify and confirm the integrity of an assembled sterilisation filter before and after use. Testing matches the type and stage of filtrer/filtration (bubble point test, pressure hold test or diffusion rate test). Manufacturer suggests test type to use. |
| What are the parameters of integrity testing? | Pre-filtration integrity test results, duration of filtration, volume filtered, differential pressure and post-filtration integrity test results. Established during validation studies and used to monitor filtration processes. |
| What is the bubble point? | The minimum pressure required to force liquid out of the pores. Measures the pore diameter of the filter. Liquid is held in the filter by surface tension and capillary forces. Pressure required is inverse to size of the pore. Smaller pore=higher pressure. |
| What is the bubble point test? | Non destructive test, tests the integrity of the membrane by measuring the diffusional flow of a gas through a wetted filter. The bubble point if the pressure at which the liquid in the channels of the filter is driven out by the test gas. |
| What is the procedure for performing a bubble point test? | Wet the filter with appropriate fluid (water for hydrophilic, alcohol water mix for hydrophobic) Pressurise system to 80% of expected bubble point Slowly increase pressure until praid continuous bubbling is observed at the outlet. |
| What are the possible reasons when the bubble point value is lower than the specification? | Fluid with different surface tension than the recommended test fluid Integral filter but wrong pore size High temperature Incompletely wetted membrane Non-integral membrane or seal. |
Created by:
LDM
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