(T1230-02-14) Tubing and Preservative Loss during Static Holds: Analysis and Recommendations for Manufacture of Preservative Containing Formulations

Purpose: Antimicrobial preservatives are commonly used in multi-dose vial (MDV) presentations, intended to be breached by multiple syringes during use.  Sufficient preservative prevents any bacterial or fungal growth and is critical for the safety of drug products intended for a dosing period of greater than 6-hours and up to 28-days from first dose withdrawal.  Unfortunately, preservative concentration can be impacted during manufacture when held in silicone tubing; prior research suggests preservative is lost via diffusion and recommends fluoropolymer tubing as a potential alternative (Saller et al., 2017).  However, silicone tubing is widely used due to multiple advantages including its comparably lower extractable and leachable profile, cost, tensile strength under pressure, physical flexibility, and sterilization versatility—it is worth investigating silicone tubing from different vendors as well as comparable replacements. This study assessed existing biopharma compliant tubing options which include silicone tubing from different vendors and alternative (non-silicone) options to compare preservative retention capabilities and generate recommendations for manufacture of preservative containing formulations.

Methods: Multiple tests were conducted during this tubing assessment which included static holds of 2-phenoxyethanol (2-PE) solution within different tubing candidates and a morphological inspection of tubing pre- and post-exposure.  A tubing size of 3.2 mm inner diameter x 6.4 mm outer diameter was utilized for all tests and only single-layer, unbraided tubing was tested; this eliminated the additional variables of tubing thickness and layering.  All selected candidates are suitable for biopharmaceutical processes, can be utilized with a peristaltic pump, and have no known incompatibility with the selected preservative or phenol.  Six different platinum-cured silicone and two thermoplastic elastomer (TPE) tubing candidates were examined by the study methods.  Polytetrafluoroethylene (PTFE) and perfluoroalkoxy (PFA) tubing were utilized as chemically inert controls—these controls are not suitable candidates due to their rigidity, sterilization limitations (for gamma radiation of single-use systems), and potential concerns regarding future PFAS regulation.  Controls and candidates were filled with solution and sealed until pre-determined timepoints were reached. At each timepoint, the entire volume was collected and the tubing saved for morphological analysis.  Resulting samples were tested for concentration by high-performance liquid chromatography (HPLC) analysis, and the timepoint concentrations were compared against starting concentration to determine the percentage lost.  The interior of the tubing was examined and imaged using a digital microscope.

Results: 2-PE is lost continuously during static holds in both silicone and TPE tubing, but the rate of 2-PE loss is much higher for silicone than TPE.  These results were seen in both autoclaved and unautoclaved tubing.  There are only minor differences in the rate of 2-PE loss between silicone tubing from different vendors with Sartorius’s Tuflux and St. Gobain’s Sani-Tech SPT slightly outperforming the other silicones.  The TPE tubing candidates exhibited minimal loss of 2-PE.  Additionally, extended 2-PE contact does not impact the morphology of the inner tubing.  The optical microscopy images show no visual changes or deposits on any tubing post-exposure to 100% 2-PE after 96 hours.

Conclusion: Manufacture of preservative containing products presents unique challenges at the filling line which can be mitigated by utilizing non-standard materials.  Wherever possible, TPE tubing should be used in replacement of silicone tubing during the manufacturing process to greatly reduce the rate of preservative loss.  Like silicone, TPE tubing can be sterilized via gamma radiation or autoclave and will not be impacted by any future PFAS ban by regulatory bodies.  Both silicone and TPE see preservative loss via sequential absorption, diffusion across the tubing wall, and volatilization, however, TPE can support static holds of approximately 120 times longer than silicone tubing.

References: Verena Saller, Julia Matilainen, Christian Rothkopf, Daniel Serafin, Karoline Bechtold- Peters, Hanns-Christian Mahler, Wolfgang Friess, Preservative loss from silicone tubing during filling processes.
European Journal of Pharmaceutics and Biopharmaceutics, Volume 112, 2017, Pages 109-118, ISSN 0939-6411

Acknowledgements: Affiliations and Disclaimers: Studies conducted and funded through Pfizer. Acknowledgements: Parag Kolhe, Xiaomin Jing, & Alex Langford


Tubing Materials & Abbreviation Key


Comparing Static Hold Results as Percent Loss over Time


Comparing Microscopy Images of Inner Tubing Pre- & Post-Exposure