Drug Delivery On The Go: Device Design Considerations

By Ashley Whitney, Senior Mechanical Engineer, Cambridge Consultants

Wearable devices are changing the world of drug delivery, emerging as solutions for chronic disease management and offering patients reprieve from the burden associated with frequent injections and bulky ambulatory devices.  Diabetes care is a prime example — small, wearable patch pumps are giving patients an option for more discreet and flexible treatment.

But insulin delivery is only the tip of the iceberg for body-worn devices. With developments in biologic therapies trending towards larger volumes and higher viscosities, many drugs are outgrowing their current auto-injector devices. Wearable devices also present an opportunity to move therapies from the hospital into the home in areas such as pain management and immunodeficiency.

Motivation For Body-Worn Devices

Chronic diseases are on the rise across the globe and their prevalence is increasing the motivation for self-administered, at-home treatment — an area ripe for wearable drug delivery technology, such as patch pumps. The patient burden of care for chronic diseases is great and comes with frequent reminders to patients that they are living with an illness.  Wearable devices help minimize this burden of care by improving treatment flexibility, patient experience, and therapy compliance:

Flexibility

Many traditional self-administered injectables for chronic disease management require a patient to frequently set aside time at home to prepare and deliver injections.  Imagine replacing these frequent rituals with a wearable device that could be applied in the morning and worn while getting ready for work or school, allowing a short-term, controlled delivery over five or 10 minutes that happens in the background of a patient’s daily life.

Wearable devices could also enable the transition of therapies traditionally delivered in the hospital into the home, resulting in shorter hospital stays. In the case of pain management, a wearable device could provide freedom from traditional patient-controlled analgesia pumps post-surgery, which are bulky and complicated to use.

Patient Experience

Wearable devices can improve a patient’s interaction with his or her therapy. For instance, for diseases like rheumatoid arthritis (RA) and multiple sclerosis (MS), which affect manual dexterity — or even just for an ageing population — wearable devices can help to minimize the device manipulation required by patients. 

Wearable devices could also be used to slow the delivery rate of injections, providing less painful injections for larger volume or high-viscosity drugs. 

Compliance

Compliance issues can arise from frequent dosing requirements associated with chronic disease management. For many chronic diseases, weekly or daily injections are not uncommon. 

Some of the need for frequent injections can be attributed to the limitations of subcutaneous injection volumes.  For subcutaneous injectables, dosing volume is limited by physiological and anatomical constraints. Typically, no more than 1.5 mL of drug can be introduced to a patient in a single injection without risk of unacceptable pain or drug loss. Depending on drug formulation, this limits the total amount of active ingredient that can be delivered to a patient in a single dose. 

However, if a device solution were able to provide controlled delivery of larger volumes over the course of seconds or minutes, higher dosages could be achieved in a single delivery event, allowing for less frequent injections.

Body-Worn Device Selection Considerations

Motivation for body-worn devices is clear, but when it comes to new applications for wearable delivery, a one-size-fits-all device approach is unlikely to be effective. As with other self-administered drug delivery devices, such as auto-injectors, a wearable delivery device must not only address specific drug needs, but also therapeutic needs related to the target application. For wearable devices, considerations around dose accuracy, safety, wear time, primary packs, and ergonomics will need to be made to ensure the device is appropriate for a specific application:

Dose Accuracy

Many wearable devices today have infusion-based mechanisms that closely regulate flow rate.  Although this level of control is necessary for insulin delivery, many bolus-based biologic and pain management therapies do not require precision in flow rate control. For drugs that consider dose accuracy in terms of bolus volume and not flow rate, pressure- or volume-based delivery mechanisms could address dose accuracy needs with less complexity and at a lower cost.

Safety

There are a number of safety considerations that will apply across injection devices, such as sterility and sharps protection.  On top of these, however, drug or therapy specific safety considerations will need to be considered in some cases.  For example, in pain management, prevention of overdose or drug abuse might require device lockouts, tamper resistance, or time-delayed bolus injection.

Wear time

For applications such as large-volume biologics, device wear time is on the order of minutes rather than days, as is required for insulin pumps.  This means that use environments can be more controlled — there is no need to wear a device while playing sports or showering, as is the case with a device worn 24/7 for insulin.  Robust skin attachment and low-profile form, factors critical for long-term wear, become a lower priority in these cases. Short-term, adhesive-free attachment methods could be an attractive option in some cases.

Primary Pack Integration

Many existing patch pumps and bolus injectors require filling prior to use, or incorporate a custom primary pack, which requires additional drug stability testing.  Novel delivery technologies could allow incorporation of existing primary packs already established for the target drug, providing drug manufactures with a streamlined device integration approach at the conclusion of successful early clinical trials.  

Ergonomics

For treatments addressing RA or MS, patient dexterity limitations could be addressed through an ergonomic form factor with easy-to-activate controls. Ergonomic considerations could also be made to address the body locations of device wear.  Typically, patch pumps would be applied on the abdomen, lower back, or upper arm, and would rotate over the course of a patient’s therapy.  Therefore, devices should be easy to apply, activate, and monitor in any of these locations. 

The opportunities in wearable devices are vast. As drugs evolve to improve patient care, however, device designs must evolve in parallel. Patients with chronic diseases do not want to be defined by their disease; wearable devices offer a brief reprieve from the reminder that they are living with an illness. Understanding the unique needs of different self-administered therapies will enable wearable drug delivery to emerge as the next platform of devices improving patient care. 

About The Author

Ashley Whitney is a senior mechanical engineer with Cambridge Consultants, a product development and technology consulting firm.  Ashley has experience in the development and commercialization of infusion and injection devices for a variety of hospital-based and patient-administered therapies.