The Challenge of Visual Inspection of Prefilled Syringes

Visual inspection of injectable products can prevent the potential of harm to patients. The FDA provides guidance for the development of a risk-based approach to detecting, controlling, and preventing visual particulates in injectable products.1 These types of products include the typical vial and syringe products and prefilled syringe combination products. But is there a difference in how these products are inspected? Does the nature of a combination product where the drug is inside the delivery mechanism create additional complications to visual inspection?

PharmTech spoke with Daniele Ansaldi, technical manager for Automated Inspection Machines at Antares Vision Group to find out what challenges prefilled syringes may hold.

PharmTech: What makes visual inspection of prefilled syringes different than visual inspection of vials?

Ansaldi: Visual inspection of prefilled syringes is more challenging than vials due to [the prefilled syringes’] geometry and handling requirements. Syringes must be oriented needle-up to detect particles resting on the plunger (stopper), adding complexity to the process. The presence of the plunger prevents bottom-up illumination and limits the use of the Tyndall effect, requiring alternative lighting from the top or sides.

The narrow barrel restricts fluid movement, often necessitating higher spin speeds to mobilize particles. Additional challenges include particles trapped between the stopper and barrel, air bubble movement during reorientation, and inspection of plunger ribs and fill level.

Are there new technologies available for conducting visual inspection of prefilled syringes?

Yes, several innovations are improving both handling and detection performance. One key advancement is the elimination of glass-to-glass contact during handling, which ensures smoother syringe transport, reduces vibration, and minimizes bubble formation that can interfere with inspection. Modern turnover devices are also designed to gently invert syringes (needle-down to needle-up), avoiding unnecessary liquid disturbance.

On the inspection side, AI [artificial intelligence]-native systems are increasingly adopted to enhance defect detection while significantly reducing false rejects. These systems learn from real production data and improve over time.

How can container closure integrity testing be automated?

Container closure integrity testing (CCIT) can be fully automated by integrating high-voltage leak detection (HVLD) directly into the automated inspection machine (AIM), enabling true 100% in-line inspection. This approach allows simultaneous cosmetic, particle, and leak detection within a single platform, improving efficiency and reducing handling.

HVLD is particularly effective for liquid-filled, conductive products in standard glass containers, with the capability to detect leaks down to approximately 2-micron pinholes under optimal conditions. Systems can reach speeds up to 400 parts per minute for prefilled syringes. At Antares Vision Group, this integration ensures robust, non-destructive CCIT is directly integrated into the inspection workflow.

How does the viscosity of liquids complicate the filling of prefilled syringes? How does it impact traditional vial/syringe delivery?

This is not related to inspection machines; however, high-viscosity or gel-like products significantly challenge visual inspection because particles do not move freely after the spinning phase. This limits the effectiveness of traditional particle inspection methods based on spin–stop–analysis, which rely on particle motion to create contrast. As a result, inspection must shift toward a more cosmetic-like approach.

At Antares Vision Group, viscous products are inspected using continuous 360° rotation with multiple image acquisitions (up to ~75 images). Advanced tracking algorithms analyze object behavior over time to determine whether a defect is internal or external, with AI-native systems supporting robust detection while minimizing false rejects.

Reference

1. FDA. Inspection of Injectable Products for Visible Particulates, Guidance for Industry. FDA.gov. December 2021. Accessed April 29, 2026. https://www.fda.gov/media/154868/download

About the Expert

Daniele Ansaldi is technical manager for Automated Inspection Machines (AIM) at Antares Vision Group North America. Daniele is responsible for defining and aligning technical solutions across the full lifecycle—from pre-sales engineering to after-sales support and leads a multidisciplinary team composed of Field Service Engineers, an automation specialist, a mechanical designer, and a project manager.

Daniele has more than 25 years of experience in the inspection industry, starting in 1999 as a Field Service Engineer and progressing through roles such as Commissioning Manager, Regional Field Manager, and Customer Service Manager with leading global AIM manufacturers.

More on Prefilled Syringes

In the April 2026 episode of Ask the Expert, Susan J. Schniepp, distinguished fellow at Nelson Labs, and Siegfried Schmitt, PhD, vice president, Technical at Parexel, address the complexities of investigating patient complaints regarding pre-filled syringe (PFS) and combination products. Schniepp and Schmitt make it clear; for manufacturers who purchase commercial syringes for their drug products, the marketing authorization holder (MAH) remains ultimately responsible for product performance, regardless of their level of control over the component manufacturer. Watch the episode here.