Applying Human Factors Engineering to Combination Products

Dec 27, 2020


On the same day of the release of the FDA CDRH Guidance on Applying Human Factors and Usability Engineering to Medical Devices in February 2016, CDER released a draft Guidance in tandem that offers special human factors considerations for combination product manufacturers. While some of the key points of the CDRH Guidance are only cosmetically reframed in the CDER Guidance to apply specifically to combination product manufacturers, there are many unique considerations throughout the document. These considerations are borne of the unique qualities of combination products, in particular the special and variant risks associated with the drug constituent part.

Here, we will examine some key ideas to consider when developing a human factors program for your combination product.

Special Considerations for Preliminary Research and Analysis

Identifying User and Use Environments

The CDRH Guidance does not make significant distinctions among non-healthcare professional users (i.e., lay users); notably, the CDER Guidance recommends to identify subgroups within groups of lay users. For example, a patient and a caregiver, while both lay users, have very different roles and capabilities as they pertain to preparing or administering medications. If both populations are indicated to use the product, you should consider the tasks and risks associated with use by each individual user group.

In our experience at ClariMed working with CDRH, it’s typically “easier” to justify equivalency between caregiver and patient groups when determining sample sizes for Human Factors Validation Testing. In contrast, CDER tends to have a higher bar for accepting such justifications. For example, CDER may require 15 participants with Rheumatoid Arthritis (RA) and 15 caregivers, while CDRH may be more amenable to inclusion of a single user group of ~8 patients with Rheumatoid Arthritis and ~8 caregivers, or even just 15 patients with Rheumatoid Arthritis and no caregivers due to RA patients being representative of a “worst-case scenario.”

Use-Related Risk Analysis

In use-related risk analysis, it is important to take into account the drug development end goals. This means that use-related hazards should be mitigated or eliminated for adverse events and medication errors attributable to use error. Oftentimes, endpoints for reducing these hazards will manifest in the development of labeling; the user-facing features of drug quality (e.g., drug appearance) will also be considered in holistic risk management activities related to combination product development.

For products indicated for home use, use errors can arise from confusion between your product and others that are stored in the same location. These may include products intended for other family members or for pets. Consider risks related to medication identification if your indicated user might have similar products in their medicine cabinet or refrigerator.

Special Considerations for Usability Testing

Selecting Critical Tasks

Notably, the CDER definition of “Critical Task” is limited to those “user tasks that, if performed incorrectly or not performed at all, would or could cause harm to the patient or user.” The CDRH Guidance specifically references “serious harm” in its definition of Critical Task [1]. This distinction can be interpreted to mean that, in the CDER realm, any use error which might cause any harm to the user (including compromised medical care) [2] must be considered a Critical Task. This reduces the threshold of severity rating for which a use-related risk might help identify a Critical Task. For example, tasks associated with risks with a severity rating of 4 or higher (where 4 meets the definition of serious injury) might be considered Critical Tasks by CDRH. Using the same severity scale, risks with a severity rating of 3 or higher might be considered Critical Tasks by CDER (where a severity rating of 3 may be associated with reversible injury not requiring medical intervention).

Due to the CDER definition of “Critical Task,” ClariMed finds it important to consider those tasks essential to completion of the workflow. Failure to perform tasks that are entirely necessary to administer a full dose of a drug might lead to patient harm in the form of compromised medical care. If these tasks have a low severity of harm, they are termed “Essential Tasks” and must be tested in Human Factors Validation Testing.

When carrying out human factors programs for combination products, ClariMed defines “Critical Tasks” to include “Safety-Critical Tasks” and “Essential Tasks.” “Safety-Critical Tasks” align with the definition of “Critical Task” per the CDRH guidance. “Essential Tasks” include lower-severity tasks to encompass all tasks called for by the CDER guidance. By dividing the concept of “Critical Task” into two categories, we can simultaneously align with both the CDER and CDRH guidances.

Determining Task Test Method

In some cases, labeling is critical in safe use of a combination product. Labeling indicating expiration date or describing individual healthcare personnel roles in a procedure are just two examples where critical information is conveyed that can have a significant effect on the outcome of device use. It is important to assess the user’s understanding of such information.

Furthermore, CDER places significant emphasis on the mitigation of adverse reaction harm due to use error throughout the Guidance; tasks related to actions taken in the event of an adverse reaction must be tested in Human Factors Validation Testing. For example, a lay user should be tested on their knowledge of contacting emergency medical services in the event that they feel certain side effects indicative of an overdose. In the case that training on the product is offered, it might be easier to test these tasks as part of the Knowledge Task Assessment. If no training is offered, it might be easier to test the findability and comprehensibility of this information in your IFU, Quick Reference Guide, or other labeling.

Determining if Actual Use Testing is Appropriate

Both the CDER and CDRH Guidances state that Simulated Use Testing should be sufficient to determine the use-safety and efficacy of the medical device or combination product. There are some cases where a combination product containing the real drug product must be tested, either in a simulated use setting or actual use environment.

There may be cases where the actual drug might affect or impair users’ abilities in completing the product workflow. For example, caustic inhalants might cause a user to cough and receive an incomplete dose. Determining the root cause of underdose is only possible, in this case, with use of the actual drug.

There are also cases where your combination product is indicated for use in emergency settings, or where your combination product has a complex workflow. Noise and distraction associated with these use conditions can only be mimicked by placing the user in an actual use environment. In this case, many of these environmental considerations can be adequately simulated, and Actual Use Testing should serve as a last resort.

Next Steps

When developing a human factors plan for your combination product, make sure to review both the CDRH and CDER Guidances to make sure you have adequately addressed the stipulations in both. It’s important to keep in mind that the CDRH Guidance is a final, published Guidance, while the CDER Guidance is still in draft form. As with any regulatory submission, we recommend developing a plan in advance of Human Factors Validation Testing and meeting with the agency for further guidance or recommendations.

ClariMed has years of experience in executing Human Factors Engineering activities for combination products. Contact us today to set up a free 1 hour consult for your project and learn more about our usability engineering services and expertise.


Applying Human Factors and Usability Engineering to Medical Devices, FDA. (February 3, 2016).

Human Factors Studies and Related Clinical Study Considerations in Combination Product Design and Development, FDA. (February 2016).


[1] See 21 CFR 803.3(w) for definition of serious injury.

[2] ISO 14971:2019 defines harm as “injury or damage to the health of people, or damage to property or the environment.”

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We’re always looking for new opportunities. If you would like to partner with us, please get in touch.

Let's work together!

We’re always looking for new opportunities. If you would like to partner with us, please get in touch.