Microbiological Deviations and Technical Deficiencies - Warning Letter to US Manufacturer

During an inspection of a US manufacturer of terminally sterilised medicinal products, the FDA identified numerous GMP deficiencies. The key issues included inadequate handling of out-of-specification (OOS) results in endotoxin testing and significant technical and hygiene deficiencies in cleanrooms and utilities. The inspection took place in March and April 2025.

Microbiological deficiencies and endotoxins

Since 2022, at least 40 bioburden tests on in-process control (IPC) samples have exceeded the specified microbiological limits; several results were 'too numerous to count' (TNTC). The detected findings included gram-negative bacteria that can produce endotoxins. Investigations remained superficial: root causes were left 'undetermined' or broadly attributed to "personnel" or "environment" without reliable evidence. In some cases, the company referred to ongoing CAPA (corrective actions and preventive actions) investigations with deadlines until 2026.

In its assessment, the manufacturer downplayed the risks and referred to the subsequent terminal sterilisation, without considering the possible effects of high bacterial counts on the success of sterilisation or endotoxin formation. However, according to the FDA, clean manufacturing conditions must also be ensured for terminally sterilised products in order to avoid microbiological contamination and the resulting endotoxins.
The firm also invalidated several OOS endotoxin results for finished, sterile injection solutions without a sufficient, scientifically justified root-cause analysis. In one case, an initially positive endotoxin result was declared invalid after retesting new dilutions without identifying the contamination source. In another, staff training was ordered although the firm's own investigation had concluded that neither personnel nor the test method was at fault. Further endotoxin deviations in other batches were first confirmed by repeat testing but later rejected because the retests were deemed non-compliant with the method; new sample preparations then produced compliant results and the original OOS findings were invalidated. In one batch, a bioburden sample was also TNTC, yet a link to the endotoxin result was dismissed because other tests (particles, sterility) were within limits. Batches with prior endotoxin deviations were released to the US market.

The FDA noted that while sterility and endotoxin tests are critical final controls, limited sample sizes mean they cannot detect all contamination. Any deviation in sterility or endotoxin testing therefore requires a complete, scientifically sound root-cause investigation and effective corrective action.

Technical deficiencies

During the inspection, the FDA also found serious deficiencies in the condition of the production rooms and technical equipment. Both the cleanrooms and the steam sterilisation system showed significant technical and hygienic deficiencies.
According to the FDA, the areas classified as ISO 5 and ISO 7 for filling, weighing and preparation were structurally and hygienically deficient and poorly maintained. Excessive amounts of silicone and adhesive tape were used to seal gaps in HEPA filters, ventilation outlets and pipes. According to the FDA, the extent and execution of these seals indicate temporary repairs that do not meet GMP requirements for permanently cleanable and maintainable surfaces.

The steam system, which is used both to supply the filling lines and, in some cases, as process steam, was also in poor or damaged condition, according to the FDA. FDA inspectors found peeling insulation, severe corrosion and leaks. Condensate was dripping from the pipes in several places; water had collected in a collection bucket at one leak site. According to the FDA, such conditions promote the growth of microorganisms and the ingress of dirt into production areas.

The environmental monitoring conducted since 2019 also repeatedly showed microbiological findings, particularly in aseptic filling. The identified germs indicated a connection with the steam system, which must therefore be regarded as a potential source of contamination. Despite CAPA measures and change controls introduced in 2023 and 2024, the 2025 inspection continued to reveal microbiological findings in the production rooms.
The manufacturer had announced that it would renovate the cleanrooms by August 2026 and replace key components of the steam system by April 2027. However, the FDA considered this timeline to be insufficient and requested accelerated corrective measures and interim solutions to ensure the integrity of the equipment and the quality of the steam produced until the renovation was complete.

Due to the severity of the deficiencies identified, the FDA recommends hiring an external GMP consultant to oversee the implementation of the necessary improvement measures and verify compliance with GMP requirements. Responsibility for remedying all systemic weaknesses remains expressly with the company's management.

The detailed warning letter can be found on the FDA website.