Combination Product Industry News & Guidance

When the Needle Doesn’t Retract: What Auto-Injector Failures Reveal About Root Cause Analysis 

Six percent of units were failing design verification. Needle retraction timing was at 350–900 ms against a ≤250 ms specification. The initial hypothesis: manufacturing variability. But the reality was a design sensitivity that no amount of process control would be able to fix permanently. This is the kind of scenario that exposes the difference between solving the immediate issue and truly understanding root cause of a failure. 

The Reflexive Response vs. The Right Response 

When auto-injector verification data shows a 6% failure rate, the pressure to act is immediate. Do you tighten tolerances, add inspection controls, escalate to the supplier? While these responses may feel productive, they do not resolve the real driver of failure. 

In this case, 5 Whys analysis traced the delayed retraction to excess friction preventing timely latch release. That’s a useful starting point; but on its own, it doesn’t point to a tangible corrective action. Paired with tolerance stack-up modeling, the team identified critical insights that the low-end plunger ramp angles combining with high-end latch radii created marginal mechanical leverage at the latch-plunger interface. With that, it was clear that this wasn’t a manufacturing problem; it was a design that worked until the tolerance window collapsed. 

What Experience Recognizes 

Combination products typically fail at interfaces. Think of drug-device, component-component, design intent-manufacturing reality. In many cases, the most revealing insights come from looking closely at these interfaces first.  

The value in using tools comes from how they’re applied and interpreted in context. In this case study, high-speed video analysis confirmed latch disengagement timing, but someone had to know where to look there and how to interpret what they saw compared to the mechanical design intent. 

This understanding allowed for a targeted corrective action: an optimized interface geometry, 15% increase in spring force, and worst-case builds incorporated into design verification testing. After implementation, 2000+ subsequent units retracted within 120–180 ms. 

The Strategic Dimension 

Root cause analysis in regulated combination products isn’t just about fixing problems. It’s about building a defensible position. The evidence trail from a well-executed RCA serves multiple purposes: design history file documentation, audit readiness, and a demonstration that your team made informed, data-driven decisions. The alternative, reconstructing reasoning after the fact, rarely holds up under regulatory scrutiny. 

When RCA is treated primarily as a compliance exercise, its broader value often goes unrealized. When done well, it can be a forcing function for design maturity by identifying where your product is robust and where it’s susceptible before the market does. 

The Expertise Gap 

Internal teams typically execute RCA methodology effectively. Where external perspective adds value is in pattern recognition: understanding which failure modes are common, where tolerance interactions introduce risk, and how those patterns show up in both design and regulatory expectations. 

That perspective typically comes from exposure across many programs. It shapes which questions get asked early, and how quickly investigations move from symptoms to root cause. 

Where does your team stand?

The auto-injector case above shows what happens when RCA goes past the surface-level fix. But every organization’s starting point looks different — some teams have the cross-functional muscle and documentation rigor already built in; others are still working reactively, investigation by investigation.

Take 90 seconds to see where your team’s RCA capability stands today, and where the highest-leverage gaps are.

AUTHOR

Parth Kothari, Senior Principal Consultant, Suttons Creek –Parth is a results-driven leader with over 13 years of experience in the regulated healthcare industry, specializing in the development and commercialization of complex medical devices and combination products. He has successfully led programs from concept through launch at global pharmaceutical and medical device organizations. Link to bio.