Understanding the Tip:
Why device functionality matters in combination product stability:
Drug-device combination products—such as prefilled syringes, inhalers, autoinjectors, and nasal sprays—must not only maintain chemical stability but also deliver accurate, reproducible doses throughout their lifecycle. Functional components like actuators, plungers, and valves may degrade, stiffen, or fail under long-term storage. Without integrated device performance checks within the stability protocol, a product may chemically remain stable but mechanically become unusable or unsafe.
Risks of excluding device checks from stability testing:
If device function is not monitored:
- Delivery failures (e.g., dose misfire, blockage) may go undetected
- User interface components may degrade and impair usability
- Regulatory agencies may challenge product reliability
- Post-market complaints and recalls may increase
Functional stability is as important as chemical stability for patient-centric combination products.
Regulatory and Technical Context:
Guidance from ICH, WHO, and FDA on combination product performance:
ICH Q1A(R2) and WHO TRS 1010 require that all properties affecting product quality and performance be evaluated throughout shelf life. The FDA’s Combination Product Quality Guidance further mandates that both constituent parts—drug and device—must retain functionality. CTD Module 3.2.P.8.3 and 3.2.R should include device functionality data to support approval.
What auditors and reviewers may request:
Inspectors often ask for:
- Device function test protocols and results at each stability time point
- Actuation force, spray pattern, dose accuracy, or priming studies
- Evidence of interaction between drug formulation and device material (e.g., plunger glide, silicone migration)
Absence of these data may lead to conditional approvals or post-approval testing obligations.
Best Practices and Implementation:
Design an integrated drug-device stability protocol:
Include:
- Chemical testing (e.g., assay, impurity, pH)
- Physical inspection (e.g., appearance, leakage)
- Device testing (e.g., dose delivery, actuator functionality, user interface integrity)
Test entire drug-device units—not just drug content—under ICH stability conditions (long-term, intermediate, accelerated).
Use validated functional test methods tailored to the device type:
Define device-specific metrics such as:
- Spray angle and plume geometry for nasal/oral sprays
- Injection force and glide testing for autoinjectors
- Dose reproducibility and priming effort for inhalers
Conduct tests at relevant stability intervals (e.g., 0M, 3M, 6M, 9M, 12M) and under stress conditions if required.
Document device performance trends and correlate with product usability:
Summarize:
- Functional pass/fail rates across time points
- Correlation between device drift and environmental exposure (e.g., cold chain, humidity)
- Any user feedback simulations from human factors testing
Reference all findings in CTD and maintain device-lot traceability throughout the study.
Aligning drug-device combination stability protocols with periodic device functionality testing ensures that the product is not only chemically intact but also mechanically reliable—delivering the right dose, in the right way, every time until expiry.