An April 2026 FDA warning letter involving a sterile injectable drug manufacturing facility is bringing renewed attention to the limitations of pharmaceutical visual inspection programs and the role qualified automated vial inspection technology can play in detecting visible particulate contamination.
According to AutomatedVialInspection.com, a warning letter was recently issued to Par Health USA, LLC and Endo USA, Inc. following an FDA inspection of the company’s Rochester, Michigan manufacturing facility. The inspection took place from October 6 through October 20, 2025, and the FDA issued the warning letter on April 15, 2026.
Among several areas discussed in the letter, the FDA devoted significant attention to the facility’s visual inspection program for sterile injectable products. The agency identified concerns involving personnel detection capabilities, particle classification, reinspection procedures, recurring glass defects, and the effectiveness of the overall inspection process for detecting visible particulate matter.
AutomatedVialInspection.com notes that the warning letter is particularly relevant for pharmaceutical manufacturers evaluating how manual, semi-automated, and automated vial inspection methods should fit into a broader quality system. The FDA’s observations reinforce the importance of inspection processes that are qualified, reproducible, product-specific, and supported by appropriate procedures and quality controls.
FDA Findings Put Probability of Detection in Focus
One of the most notable observations involved the probability of detecting visible particulates during inspection. According to the FDA, studies performed at the facility showed that personnel were often unable to achieve a 70% probability of detection for certain critical particulates larger than 150 microns, including examples such as dark fibers, light fibers, and glass.
The FDA explained that visual particulate detection is inherently probabilistic rather than absolute. The agency stated that personnel should, at a minimum, be reliably capable of detecting particulates measuring 150 microns or greater at a 70% probability of detection, illustrating why qualification must assess actual inspection performance rather than simply whether an inspection procedure exists.
That distinction is important for pharmaceutical manufacturers because the effectiveness of visual inspection depends on numerous variables. Inspector capability, lighting, inspection time, container characteristics, product appearance, particulate composition, particle size, contrast, movement, and inspection conditions can all influence whether a defect is detected.
Automation does not eliminate those variables, but it can create an opportunity to control and measure many of them more consistently. An automated vial inspection system can apply defined inspection parameters repeatedly across large numbers of containers, provided the technology has been appropriately developed, challenged, qualified, and maintained for the specific products being inspected.
Particle Classification Can Be as Important as Particle Detection
According to AutomatedVialInspection.com, the warning letter also demonstrates that detecting something inside a vial is only one part of an effective visual inspection program. The FDA stated that critical defects had been categorized as major defects in some instances, with subsequent changes in classification affecting acceptable quality limit results.
This distinction highlights the connection between inspection technology and the quality system surrounding it. An inspection process needs clearly established defect categories, representative defect standards, appropriate acceptance criteria, investigation procedures, and methods for determining what should happen when unusual or recurring defects are identified.
Automated vial inspection systems therefore should not be viewed simply as cameras placed on a production line. Their effectiveness depends on the inspection methodology behind the equipment, including how defects are defined, how representative samples are created, how detection thresholds are established, how recipes are developed for different products, and how the system is challenged against defects that manufacturers actually encounter.
Reinspection Should Not Become a Path Around Unusual Defect Levels
The FDA also raised concerns about repeated reinspection of products containing visual particulates. According to the warning letter, the facility’s procedures permitted multiple reinspections in support of batch release, while the FDA stated that reinspections should be limited and justified and that the agency generally does not recommend more than one reinspection when attempting to release a batch with atypical defect levels.
Repeated inspection can create a misleading sense that an original inspection failure has disappeared rather than identifying why the unusual defect level occurred. A strong inspection program should generate information that helps quality personnel investigate trends, understand potential sources of contamination, evaluate process performance, and determine whether corrective and preventive actions are necessary.
This is another area where automation can potentially provide value beyond individual pass-or-reject decisions. Properly designed automated systems can produce repeatable inspection results and structured inspection data that may help manufacturers analyze recurring defects, compare production runs, investigate changes in reject patterns, and identify conditions that warrant further review.
FDA Specifically Discusses Automated Visual Inspection
Perhaps the clearest connection between the warning letter and automated vial inspection appears in the FDA’s discussion of visible particulate contamination. The agency stated that it encourages the use of suitable automated visual inspection for particulates to augment the applicable visual inspection program.
Importantly, the FDA did not suggest that simply installing automated equipment is sufficient. The agency stated that automated methods should be rigorously studied and qualified to assess capability and robustness under different conditions, including machine settings, container-closure sizes, defect types, product characteristics, and other relevant variables.
This qualification requirement is one of the most important lessons for manufacturers considering automation. The relevant question is not merely whether a machine is capable of finding particles, but whether the configured inspection process can reproducibly detect the appropriate defects under the conditions associated with a specific product and production environment.
Automated inspection must also be understood as one component of a broader inspection strategy. The FDA noted that automated particulate inspection used as an adjunct does not replace the need to inspect for other attributes, which can include container or closure defects, cracks, fill volume issues, and abnormal appearance characteristics.
Automation Still Requires a Strong Quality System
The FDA’s position is consistent with its broader guidance on visible particulates in injectable products. The agency’s draft guidance describes visible particulate control as a holistic, risk-based process incorporating product development, manufacturing controls, visual inspection techniques, particulate identification, investigations, and corrective actions rather than relying on inspection as an isolated final production step.
For manufacturers, that means an automated vial inspection system cannot compensate for weaknesses elsewhere in the manufacturing process. Recurring particulate contamination still requires investigation, root-cause analysis, appropriate supplier controls, process improvements, CAPA, trending, and quality unit oversight.
The Par Health warning letter illustrates this connection through its discussion of recurring adhered glass defects. The FDA stated that these defects had not been adequately detected and addressed by the visual inspection program and requested changes involving supplier qualification, inspection qualification practices, CAPA, deviation investigations, and other parts of the manufacturer’s quality system.
In other words, better detection should ideally lead to better information about the manufacturing process. When inspection data indicates an emerging problem, manufacturers need procedures capable of turning those observations into investigations and corrective actions rather than treating rejected containers solely as isolated production losses.
What Pharmaceutical Manufacturers Can Learn From the Warning Letter
The broader lesson from the FDA warning letter is not that automated vial inspection eliminates inspection risk. Instead, it demonstrates why pharmaceutical manufacturers need inspection programs capable of producing reliable, reproducible, and scientifically supportable results across the products and containers they manufacture.
Facilities evaluating their existing programs may want to examine whether their inspection methods are consistently detecting representative particulate types, whether personnel and equipment qualification reflect actual production defects, and whether difficult-to-inspect products require additional technologies or methods. Manufacturers can also review whether defect classifications are clearly defined and whether unusual reject rates trigger meaningful investigations instead of repeated inspection.
For companies considering automated vial inspection, qualification should be part of the discussion from the beginning. Product characteristics, vial dimensions, closure systems, expected defect types, particle properties, inspection speeds, equipment settings, lighting, imaging technology, reject criteria, and challenge samples can all influence the performance of an automated inspection process.
The April 2026 FDA warning letter provides a timely reminder that visual inspection is not simply a production-line formality. For sterile injectable manufacturers, it is part of a larger system intended to identify visible defects, generate actionable quality information, and provide confidence that finished products meet established quality requirements.
Manufacturers reviewing their current inspection processes can visit AutomatedVialInspection.com to learn more about automated vial inspection and the considerations involved in evaluating inspection technology for pharmaceutical production.
About AutomatedVialInspection.com
AutomatedVialInspection.com focuses on automated vial inspection for pharmaceutical manufacturing and quality control applications. The website provides information for organizations evaluating how automated inspection technology can fit into modern vial inspection processes and broader pharmaceutical quality programs.
Contact Information
Contact: Pepe Davila
Company Name: AutomatedVialInspection.com
Address: 1555 Commerce Dr, Bourbonnais, IL 60914
Email: info@autoamtedvialinspection.com
Media gallery
