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Published on: February 13, 2016
Sterility Test Conditions for Purified Sodium Hyaluronate Injection Evaluated via Membrane Filtration.
Katsuhiko Hayashi1, Kenji Ohya1, Yukiko Hara-Kudo1,2
1Division of Microbiology, National Institute of Health Sciences (NIHS), 3-25-26 Tonomachi, Kawasaki-ku, Kawasaki 210-9501, Japan.
Biological & Pharmaceutical Bulletin
|June 24, 2026
Summary
Both direct inoculation (DI) and membrane filtration (MF) are suitable for sterility testing of hyaluronic acid (HA) injections. This study found no microbial growth after 14 days using either method for HA-based products.
Area of Science:
- Pharmaceutical Sciences
- Microbiology
- Medical Device Manufacturing
Background:
- Sterile preparations necessitate rigorous sterility testing, with membrane filtration (MF) and direct inoculation (DI) being standard pharmacopeial methods.
- MF is favored for filterable aqueous products due to high sensitivity, while DI is often used for medical devices where microorganism elution is challenging.
- Hyaluronic acid (HA) injections present a unique case, classified as drugs in Japan but medical devices in Europe and the US, with differing sterility testing mandates.
Purpose of the Study:
- To evaluate the suitability of both membrane filtration (MF) and direct inoculation (DI) for the sterility testing of hyaluronic acid (HA)-based injection products.
- To compare the efficacy of MF and DI in detecting microbial contamination in HA-based injections, considering their varying regulatory classifications.
Main Methods:
- Direct Inoculation (DI): HA-based injection was added to culture media at a maximum concentration of 0.25 mg/mL HA. Bacterial and fungal growth were monitored.
- Membrane Filtration (MF): The HA-based injection was diluted in a 0.1% peptone-0.1% polysorbate 80 solution, filtered, and the membrane washed twice before incubation.
Main Results:
- Microbial growth was observed within 3 days for bacteria and 5 days for fungi in culture media containing 0.25 mg/mL HA during DI method validation.
- All tested bacteria and fungi showed growth in the culture medium during the MF method validation.
- Crucially, no microbial growth was detected after 14 days of incubation for the HA-based injection product using either the DI or MF sterility testing methods.
Conclusions:
- Both direct inoculation (DI) and membrane filtration (MF) methods are suitable for performing sterility tests on hyaluronic acid (HA)-based injection products.
- The findings support the use of either DI or MF for ensuring the sterility of HA injections, regardless of their regulatory classification.
