Clinical Equivalence: When Similar Outcomes Are Not Enough

Written by HATEM RABEH, MD, MSc Ing

Your Clinical Evaluation Expert And Partner

in
S

This happens more often than it should. Teams invest months building equivalence claims, collecting literature, comparing performance data, and then face rejection during assessment. The reason is always the same: they focused on the outcome instead of understanding what equivalence actually means under MDR.

The confusion is understandable. Before MDR, the bar was lower. Many legacy devices made it to market with equivalence claims based on loose comparisons and similar intended use. That approach no longer works. MDR Article 61(5) and Annex XIV Part A define equivalence in strict technical and biological terms. The regulation does not ask if two devices produce similar results. It asks if they are equivalent in design, materials, specifications, biological characteristics, and manufacturing processes.

Similar outcomes can hide fundamental differences that matter to safety and performance. This is the blind spot.

What Equivalence Actually Requires

Under MDR, equivalence is not a clinical judgment. It is a technical and biological assessment with clinical confirmation. MDCG 2020-5 makes this explicit. The guidance lists three cumulative criteria that must all be satisfied before a device can be considered equivalent to another.

First, the devices must have the same intended purpose. This means identical indications, patient populations, and clinical conditions. Similar is not the same. A device for moderate stenosis is not equivalent to one for severe stenosis, even if both address coronary artery disease.

Second, the devices must use the same technical and biological characteristics. This is where most claims fail. The regulation defines this as identical materials in contact with the body, similar design and manufacturing, and equivalent energy delivery or mechanism of action. Any deviation must be justified as not affecting safety or performance.

Third, clinical data from the equivalent device must be applicable to your device. This requires demonstration, not assumption. You must show that any differences do not create new risks or reduce clinical benefit.

Now the question becomes: how do you demonstrate this? And where do teams go wrong?

Why Similar Outcomes Fail the Test

I see this pattern in almost every deficiency letter related to equivalence. The manufacturer presents clinical studies showing that both devices achieve the target endpoint. Complication rates are comparable. Success rates align. The clinical evaluation report concludes that the devices are equivalent.

The Notified Body responds: this does not demonstrate equivalence. Why?

Because clinical outcomes reflect the endpoint, not the pathway. Two devices can reach the same clinical result through different mechanisms, with different risk profiles, and under different conditions. The regulation requires you to prove that the biological and mechanical pathway is equivalent, not just the destination.

Take two drug-eluting stents. Both reduce restenosis rates to similar levels. One uses a biodegradable polymer, the other uses a durable polymer. The outcomes are similar, but the biological interaction with tissue is fundamentally different. Polymer degradation creates a different inflammatory response. Long-term endothelialization follows a different timeline. These are not equivalent devices, even if twelve-month patency rates align.

The clinical data from the predicate cannot be transferred unless the biological mechanism is the same. Similar outcomes confirm effectiveness but do not demonstrate equivalence.

This is where the logic chain breaks. You cannot skip the technical assessment and jump to clinical validation. The technical equivalence must be established first, and then confirmed by clinical data.

The Technical Equivalence Dossier

What does a compliant equivalence demonstration look like? It starts with a structured technical comparison that addresses every element listed in MDCG 2020-5.

You need a side-by-side comparison of materials in contact with tissue, including grades, surface treatments, and any coatings. You need design specifications: dimensions, geometries, mechanical properties, and tolerances. You need manufacturing process descriptions and quality control parameters.

For active devices, you need equivalent energy outputs, delivery mechanisms, and control systems. For drug-device combinations, you need equivalent drug formulations, release profiles, and dosing mechanisms.

Every deviation must be identified and justified. If your device uses a different alloy, you must explain why this does not change the biological response. If the thickness varies, you must show that mechanical performance remains equivalent. If the surface finish is different, you must demonstrate that tissue interaction is unaffected.

This is not a formality. Notified Bodies review this line by line. If the technical comparison is incomplete or superficial, the equivalence claim will not be accepted, regardless of how strong the clinical data appears.

Once technical equivalence is established, you can use clinical data from the predicate to support your device. But the technical foundation must be solid first.

The next issue is access to this technical information. How do you get detailed specifications for a competitor’s device?

The Data Access Problem

This is the practical barrier that stops many equivalence claims. You do not have internal design documents for the predicate device. You do not have access to material grades or manufacturing processes. You have marketing materials, instructions for use, and published literature. That is rarely enough.

Some manufacturers attempt to reverse-engineer the predicate through physical analysis. This can provide material composition and dimensional data, but it will not give you manufacturing tolerances, process controls, or quality specifications. The information gap remains.

Other manufacturers rely on published technical papers or regulatory submissions. This works when the predicate has been extensively characterized in literature, but most devices do not have that level of transparency.

The regulation acknowledges this challenge but does not lower the bar. If you cannot access the data needed to demonstrate technical equivalence, then equivalence cannot be claimed. You must generate your own clinical evidence through animal studies and clinical investigations.

This is why many equivalence claims collapse during Notified Body review. The manufacturer believed equivalence was achievable based on clinical similarity, but the data needed to prove technical equivalence was never accessible.

There is no shortcut here. Either you have the technical data to demonstrate equivalence, or you do not. If you do not, the path forward is clinical investigation, not creative interpretation of published outcomes.

When Equivalence Is Actually Valid

Equivalence is not impossible. It works when the manufacturer has a clear predicate with accessible technical data and a genuinely similar design. This typically happens in three scenarios.

First, when the manufacturer is claiming equivalence to their own previous generation device. The technical data is internal, the design evolution is documented, and the differences are controlled. This is the cleanest equivalence path.

Second, when the predicate is a well-characterized device with extensive public technical documentation. Some established devices have been analyzed in detail in regulatory and scientific literature. If the technical specifications are publicly available and you can verify them, equivalence may be demonstrable.

Third, when the predicate manufacturer provides technical data through a formal agreement. This is rare, but it happens in licensing or partnership arrangements. If you have access to design files, material certifications, and process documentation, the equivalence claim can be substantiated.

In all three cases, the same rule applies: demonstrate technical equivalence first, then confirm with clinical data. The clinical data serves to validate that the technical equivalence translates to equivalent clinical performance. It does not replace the technical demonstration.

If you cannot meet these conditions, equivalence is not viable, and attempting to force it will only delay your project and increase regulatory risk.

How to Structure the Equivalence Argument

When equivalence is valid, the clinical evaluation report must present the argument in a logical sequence that aligns with MDCG 2020-5.

Start with a clear statement of equivalence claim and identification of the predicate device. Include manufacturer, model, regulatory status, and clinical history. Confirm that the predicate has an established safety and performance profile over a sufficient duration.

Then present the technical comparison. Use tables to map materials, dimensions, mechanical properties, and design features side by side. Highlight differences and provide justifications for each one. Reference test reports, material certifications, and design documentation.

Follow with the biological comparison. Address biocompatibility, tissue interaction, degradation or wear behavior, and any biological activity such as drug release or electrical stimulation. Again, justify any differences.

Once technical and biological equivalence is established, present the clinical data from the predicate. Include pivotal studies, post-market data, registries, and any relevant literature. Explain how this data applies to your device given the demonstrated equivalence.

Finally, address any gaps. If certain clinical conditions were not studied in the predicate, explain how you will cover them in your PMCF plan. If there are minor technical differences, explain how post-market surveillance will monitor for any unanticipated effects.

This structure shows the Notified Body that equivalence is not assumed—it is demonstrated through systematic comparison and justified through data.

What Happens When Equivalence Fails

When a Notified Body rejects an equivalence claim, the consequences are immediate and significant. The clinical evaluation report no longer meets MDR requirements. The device cannot proceed to certification without additional clinical evidence.

The manufacturer must then generate original clinical data. This typically means animal testing to assess biological safety and performance, followed by a clinical investigation to confirm safety and performance in humans. The timeline extends by years. The cost increases substantially. The project may no longer be commercially viable.

This is why equivalence must be assessed rigorously during the planning phase, not discovered as a problem during Notified Body review. If the technical data is not available, if the design differences are significant, if the biological interaction is not identical, equivalence is not the right path.

Better to plan for a clinical investigation from the start than to waste time and resources on an equivalence claim that will not survive scrutiny.

The Real Standard

Equivalence under MDR is not about finding a similar device and borrowing its data. It is about proving that two devices are so similar in technical, biological, and clinical terms that the safety and performance data from one can reliably predict the safety and performance of the other.

Similar outcomes are evidence of effectiveness, but they are not evidence of equivalence. Equivalence is a technical demonstration, confirmed by clinical data, not replaced by it.

When you see a device with similar clinical results, ask the next question: is the pathway to those results equivalent? Are the materials the same? Is the biological interaction identical? Is the design mechanically equivalent?

If the answer to any of these is no, then equivalence is not valid, and you need original clinical evidence.

This is the distinction that separates accepted submissions from rejected ones. It is not about interpretation. It is about meeting a defined technical standard before making a clinical claim.

Peace,
Hatem
Clinical Evaluation Expert for Medical Devices
Follow me for more insights and practical advice.