Designing Drug Delivery Devices For Usability

By Debbie McConnell and Scott Ulrich, Battelle

Usability is a critical factor for all medical devices, but drug delivery devices come with their own unique challenges. Incorporating human-centric design (HCD) into drug delivery device design can minimize the occurrence of use errors that result in dosing problems and other risks to patient safety.

Designing for usability requires a clear understanding of user needs and limitations, as well as the environment in which the device will be used. Devices used at home by patients have different requirements than devices used in the clinical environment, but both types of device have some common usability needs. To ensure appropriate use and proper dosages, drug delivery devices must support users throughout the dosing process and incorporate best practices in user interface (UI) design, physical device design, and user communication.  

Support Users Through The Entire Dosing Process

To ensure safe use of the device and proper dosing, users — whether home- or clinic-based — need support through the entire dosing process. Manufacturers need to consider three distinct phases: preparing the device for use; administering the dose; and either disposing of the device or dissembling, cleaning, and storing the device so it is ready for the next use.

The best way to support users is through “directed use.” That is, incorporate design choices that allow the device itself to direct users in its proper operation. This may include both physical design and software UI design. For example, contoured sides and a flat bottom on an inhalation device may provide clues as to proper orientation, or a screen display may use guiding prompts or indicators to provide clear feedback during use. The more users can rely on the device itself to tell them what they should do, rather than separate instructions, the more likely they are to follow the appropriate dosing procedure.

Devices for home use need to be simple and require very little instruction. For home users:

• The device should indicate to the patient what state it is in (e.g., ready to use, dose being delivered, dose complete) and direct the patient through each stage of the process.
• Many medical devices for home use have a very small UI screen, so instructions need to be short and direct with text as large as possible. For example, a home inhalation device with a screen might say “ready” to indicate that the device is ready to deliver a dose, “inhale” during use, and “done” to indicate that the correct dose has been delivered.
• In general, it’s better to use words — with translations available for non-English speakers — than pictograms, which can be easily misinterpreted. If you are using lights or sounds (as well as, or instead of, screen displays), use simple colors and a few audible combinations to tell the patient that the device is “ready to go” or “can’t deliver a dose.” Avoid complex, blinking patterns.

Directive UI also is  critical in the clinical environment. In such environments, one healthcare provider may start a drug delivery process and another may complete the treatment. For example, when a drug is delivered over an extended time, such as infusions or IV drips, dosing may occur across a shift change. This makes it especially critical to have easy-to-read status indicators and clear, step-by-step instructions. Clinical devices often have larger UI screens than home devices, allowing more information to be presented. Some best practices for the clinical environment include:

• Make status indicators clearly visible from across a room, so busy healthcare providers can see at a glance whether the device is operating normally, needs attention, or has completed the dosing process.
• Provide simple on-screen checklists that guide teams of healthcare providers through the process, and make it clear which step comes next. If device sensors cannot be used to automate detection of step completion, healthcare providers should be required to manually confirm completion of each step before instructions for the next step are provided.
• If the UI allows, make different levels of information available for each step. Giving healthcare providers the option to access additional instructions or detailed diagrams, as needed, accommodates providers with varying levels of experience.

Understand Predicate Products

When designing a drug delivery device, it is important to understand the products it may replace or compete with. Patients and caregivers who are used to the way their current device operates will expect new devices that look similar and also operate in a similar manner. Manufacturers introducing a new product should either:

• Design a product that is similar to familiar devices in both appearance and operation, or
• Introduce a product that is dissimilar enough in form and appearance to indicate to users that it should be used in a new manner.

Products that look similar to familiar devices, but are not intended to be used the same way, are likely to cause confusion that could lead to use errors, resulting in improper dosing or other safety concerns. For example, inhalers have looked and operated in much the same way for decades. Patients who currently use inhalers will expect future devices that appear to be inhalers to work the same way.

Nurses and other healthcare providers also rely on familiar mental models when introduced to a new device that seems to operate in similar fashion to another device. They may interact with several devices over the course of a shift, and it can be challenging to keep use instructions for all of these devices straight. Additionally, some devices may be used infrequently. For example, a new neonatal nebulizer system may look and behave similarly to an existing device that is used regularly, but it could require new steps for use because it is only intended to treat specific patient conditions. Manufacturers should consider these existing mental models when introducing new technologies that replace familiar ones.

Design Clear Alarms And Alerts

Drug delivery devices need to clearly indicate when all is well and when they need attention. In the home environment, patients generally only need two types of alerts: 1) something good has happened (e.g., the dose is complete), or 2) the device needs them to do something before a dose can be delivered (e.g., refill a drug). In designing alerts, keep these best practices in mind:

• Use alerts sparingly, and only for urgent information. Users tend to ignore alerts if they are used too frequently or for non-critical information.
• Use simple, consistent, and universally recognized visual or auditory cues for alerts. For example, in the U.S., a rising tone generally is recognized as indicating something “good,” and a falling or discordant tone generally is recognized as indicating something “bad.” Similarly, green, yellow, and red lights typically are used to indicate “all is well/proceed,” “caution/needs attention,” and “stop/critical problem.”
• Multisensory alerts (e.g., aligning the “Dose Complete” message with a green light and rising tone) are most effective.

The same principles apply in the clinical environment. However, healthcare providers also appreciate a countdown and indicators that warn them when action will be needed soon. The UI and alert system should provide a clear indication not only of what needs to happen next, but when the action needs to happen, or how long the healthcare provider has to complete the action. Knowing that there are only five minutes left in the dose delivery, and that another action will need to happen within ten minutes of dose completion, is critical information for healthcare providers juggling care for multiple patients.

Design For Correct Dosing

One of the biggest challenges in drug delivery is ensuring that the patient has received the correct dose of medication. Devices that give patients and healthcare providers clear indications of dose delivery and completion can help to ensure that proper dosage is achieved.

For some types of drug delivery, such as IV bags or standard syringes, it can be easy to tell that a drug is being successfully delivered. In other cases, the patient or healthcare provider may not be able to see the drug as it is delivered. This can lead to use errors, such as pulling out an autoinjector before the dose is complete or stopping a nebulizer treatment too early. Manufacturers can help patients ensure dose accuracy in several ways:

• If dosing progress is not obvious, give users a visual indicator, such as a progress bar to show that dosing is not yet complete.
• It often is helpful to give users a countdown (drug remaining) or a timer (time left to complete dose). These should always count down to zero, rather than up.
• Give users a clear and unambiguous “dose complete” indicator.

Drugs are only effective if they are delivered accurately and consistently. By incorporating the principles of human-centric design from the earliest stages of device design, manufacturers can reduce the risk that problems will be discovered during human factors validation testing, or after the product is on the market.

About The Authors

Debbie McConnell has 25 years of experience working with product development teams in private industry, public service and government agencies, specializing in Human Factors. As a Human Factors Lead at Battelle, she leads teams focused on identifying and delivering design solutions that exceed customers’ expectations and promote safe use. She has hands-on experience across all phases of the project development lifecycle, including user research-based design inputs, use error analysis, prototyping, usability testing, summative validation studies, regulator body submissions and product launch support.

Scott Ulrich has more than 20 years of experience working on large and small multi-disciplinary product development teams. As a Senior Industrial Designer in Battelle’s Human Centric Design Group, he has contributed to projects for both consumer and medical markets, including home-use injection devices, clinical diagnostic equipment, clinical patient care systems, and consumer electronics. He currently serves as a Design Lead on medical device development programs, establishing user needs, guiding design teams’ execution of UI and industrial design concepts to address specific user needs, and devising design strategies to establish end-product visual brand language. He also is experienced in conducting human factors testing to provide evidence of design effectiveness.