ChP 2025 vs. USP <1104>: Practical Syringe Testing Guide

Why Prefilled Syringe Testing Is Under More Scrutiny

Prefilled syringes (PFS) and cartridges are now central to many biologics and high‑value injectables. A syringe that is difficult to actuate or shows irregular force can cause dosing errors, patient discomfort, and even treatment refusal. Regulators have therefore tightened mechanical performance requirements and clarified how forces should be measured over time.

From a quality and regulatory perspective, syringe force data must be both accurate and traceable. It is no longer enough to show that “the plunger moved.” QA teams need objective, reproducible force curves that distinguish the initial break‑loose event from the sustained gliding behavior throughout the stroke.

Key Update 1: ChP 2025 General Chapter 4015 (China)

ChP 2025 General Chapter 4015 introduces stricter guidance for rubber stopper puncture and syringe force testing. One of the most important changes is the emphasis on force measurement accuracy at low loads. For typical small‑volume syringes, clinically relevant events happen in roughly the 1–10 N range, not at hundreds of newtons.

To capture these subtle differences, the chapter explicitly calls for a recording accuracy of approximately ±0.25 N for puncture force. In practice, this pushes laboratories away from generic 500 N load cells with 1 % of full‑scale error, which can easily translate into ±5 N uncertainty. Such large errors make it impossible to detect early signs of silicone lubrication failure, stopper coring, or excessive needle penetration resistance.

Key Update 2: USP <1104> Plunger Motion (USA)

USP <1104> focuses on the dynamic behavior of the plunger during administration. It clearly separates two critical force metrics:

• Break‑loose force: The initial peak force required to start plunger movement from rest.

• Gliding force: The average force required to maintain a constant movement once the syringe is in motion.

In real syringes, the break‑loose event can happen in a very short time window. If the test system samples too slowly, the true peak is underestimated or completely missed. This leads to an artificially “smooth” curve and can mask stick‑slip phenomena that would be felt by a clinician or patient during injection. High data acquisition rates and appropriate filtering are therefore essential for compliant testing.

What This Means for Load Cells and Sampling

Traditional tensile machines in packaging and general materials labs often use high‑capacity sensors to cover a wide application range. While this is convenient, it is not aligned with current syringe guidance. Large sensors reduce resolution near zero, and low sampling rates flatten out critical peaks. For PFS and rubber stopper testing, laboratories now need:

• A dedicated low‑capacity sensor sized for the expected force range.

• A data acquisition system with sufficient frequency to resolve short‑duration peaks.

• Software capable of distinguishing and reporting break‑loose and gliding segments.

The KHT MED‑01 Approach in Real Labs

The KHT MED‑01 series was designed specifically around these requirements. In a typical qualification project, a lab connects MED‑01 to its syringe fixtures and configures a 50 N high‑precision load cell. The working range is chosen so that the syringe forces sit near the middle of the capacity, where linearity and resolution are optimal.

Using this configuration, the system can achieve approximately ±0.25 N force accuracy and capture the entire force–displacement curve with a high sampling rate. Break‑loose peaks, gliding plateaus, and any stick‑slip oscillations can be clearly identified. This gives QA and regulatory teams confidence that the data reflects real in‑use behavior of the syringe, rather than artifacts of the measurement system.

Mapping Requirements to Equipment Selection

When planning syringe projects under ChP 2025 and USP <1104>, laboratories should review their existing mechanical testers and ask:

• Does the load cell capacity and accuracy support the 0–20 N range with sufficient resolution?

• Can the instrument’s sampling rate reliably capture short‑duration force peaks?

• Are the fixtures appropriate to hold syringes and stoppers without introducing bending or misalignment?

• Does the software allow separate reporting of break‑loose and gliding forces?

For labs upgrading from older general‑purpose testers, a dedicated configuration such as the MED‑01 with a 50 N sensor and syringe‑specific fixtures is often the most straightforward path to compliance. It reduces the risk of borderline data and simplifies audits, because the test conditions clearly align with the expectations of both NMPA and FDA reviewers.