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An evaluation of preservative adsorption onto nylon membrane filters
D E Guilfoyle1, R Roos, S L Carito
1Food and Drug Administration, Department of Health and Human Services, Brooklyn, New York.
Abstract:
Pharmaceutical drug products often contain antimicrobial agents as a preservative in their formulation. These excipients are required to destroy or impede the growth of microorganisms that inadvertently enter the product during manufacturing. Unfortunately, these preservatives may also interfere with microbiological assays used to determine product sterility or bioburden levels. The extent of interference by these preservatives can be quite significant, but varies depending on the method used. The most frequently used method for testing parenteral drug products is the membrane filtration technique. Membrane filters are composed of a wide variety of materials such as cellulose, polycarbonate, acrylic polypropylene, Teflon, and nylon. This study evaluated the adsorption characteristics that nylon filters, obtained from five different manufacturers, had on the filtration of solutions of four different antimicrobial compounds (phenol, methylparaben, propylparaben, and benzalkonium chloride). The adsorption properties were determined using both HPLC and microbiological assay techniques. The data revealed that there was a wide range in the amounts of antimicrobial agent (2.3 to 94.1%) bound to the membrane filters when direct product filtration was used without a subsequent rinse step. However, when a rinse step is included, only propylparaben showed any significant "true" adsorption (less than 1 to 33.3%), but showed only marginal bacterial inhibition. Interestingly, the microbiological assays indicated that with a saline rinse step, only benzalkonium chloride was lethal for the two challenge organisms even though the percent adsorbed as measured by HPLC was below 1%. This discrepancy is significant because it demonstrates the analytical limitation when using HPLC to detect minimal concentrations of benzalkonium chloride that may be deleterious to microorganisms.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Antimicrobial preservatives in pharmaceuticals can interfere with sterility testing. Nylon filters showed variable adsorption, but rinsing minimized this, though benzalkonium chloride remained lethal to microbes.
Area of Science:
- Pharmaceutical Science
- Analytical Chemistry
- Microbiology
Background:
- Pharmaceutical formulations often include antimicrobial preservatives to prevent microbial contamination.
- These preservatives can interfere with microbiological assays, impacting product sterility and bioburden testing.
- Membrane filtration is a common technique for these assays, with filter material influencing results.
Purpose of the Study:
- To evaluate the adsorption characteristics of nylon membrane filters from different manufacturers.
- To assess the impact of four antimicrobial compounds (phenol, methylparaben, propylparaben, benzalkonium chloride) on nylon filters.
- To compare adsorption data from High-Performance Liquid Chromatography (HPLC) and microbiological assays.
Main Methods:
- Nylon filters from five manufacturers were tested with solutions of four antimicrobial agents.
- Adsorption was quantified using HPLC.
- Microbiological assays were performed to assess the antimicrobial activity of filtered solutions.
- A rinse step was incorporated to evaluate its effect on adsorption and activity.
Main Results:
- Without a rinse step, antimicrobial agent adsorption to nylon filters ranged from 2.3% to 94.1%.
- With a rinse step, only propylparaben showed significant adsorption (<1% to 33.3%) but had marginal bacterial inhibition.
- HPLC showed <1% adsorption for benzalkonium chloride, yet microbiological assays confirmed its lethality to challenge organisms.
Conclusions:
- Nylon filter material can significantly adsorb antimicrobial preservatives, affecting assay accuracy.
- A rinse step is crucial to minimize preservative adsorption and accurately assess filter performance.
- Discrepancies between HPLC and microbiological assays highlight limitations in detecting low-level, biologically active preservative concentrations.