The Diskus, a Dry Powder Inhaler (DPI), currently returns several billion pounds per year in revenue and could be considered the most commercially successful inhaler. Following World Asthma Day, Design Development Engineer, Rob reverse-engineered GlaxoSmithKline’s Diskus to review its function and answer some frequently asked questions about its design:

About the Diskus Inhaler:

The Diskus can be traced back to the 1990’s when CFCs and repeatability of dose were recognised as issues with metered-dose inhalers (when I think of an inhaler, I probably think of an MDI). The idea was to create an inhaler that could dispense the drug as dry powder, removing the need for a propellent filled pressurised cannister, whilst providing a consistent measured dose to the user.

The Diskus is used to dispense various respiratory medications, you will see versions of the same inhaler branded to contain salbutamol (Ventolin), Fluticasone/salmeterol (Advair) and Salmeterol (Serevent), mainly helping to treat Asthma and occasionally COPD.

Such has been the success of the device; GSK recently sold their 1 billionth Diskus! When developing the device, GSK took a user first approach, looking to develop a robust device that contained a good quantity of doses and that was accepted by users in place of the popular MDIs at the time. Unlike many other inhalers, the Diskus uses ‘sealed blisters’ that have good resilience to perform under various environmental factors.

The main challenge for a DPI is to control the administering of the drug so that efficacy is high without the use of a propellent, as various people have different strengths of breath. The Diskus tackles this by locating the unsealed blister as close to the mouth as possible.

Other approaches for DPIs include Handihaler and Aerohaler which are reusable but, take a single capsule inserted by the user. Alternatively, Turbuhlaer and Easyhaler take a measured dose from a reservoir.

Upon First Inspection of the Diskus:

When first presented with the Diskus in its closed position, it looks solid and protected from the rigors of everyday carrying with a thick rotating cover over the mouthpiece. The cover is slightly larger than the body of the device and has indented lines that appear grippy, signifying that this is the section to be interacted with.

After interacting with the cover, it affords a rotation around the devices centre, clicking into both the open and closed position. The mouthpiece somewhat resembles the shape of lips and thus signifies that your mouth should go around it. A slider is also revealed with simple play clicks down to prime the dose.

The device has a single primary action (move the slider) to prime the dose, which is comparable to an MDI such as the Evohaler, which also has one primary action – squeezing cannister down. However, the difficulty of timing the compression with breath has been removed.

The discoverability of the device is very good, and it is easy for users to form a conceptual model of how the device functions. The device appears to have good robustness, often carried at the bottom of a bag, it has sturdy construction and feels solid in the hand.

Using the Diskus:

Unlike the EpiPen, which HD previously reverse engineered, the IFUs are not printed on the device itself. This may be because the inhaler is most often self-administered, and the correct sequence will be learned through frequent use and training. The IFUs show that the inhaler has approximately 8 key steps; 4 of which include a mechanical action. We looked at the user steps and what happens mechanically inside the device;

 

PRIMING:

1: Take out the device, making sure you have checked the expiry date and have clean hands. Rotate to open the inhaler cover and reveal the mouthpiece. The cover should click into the open position.

2: To prime the dose, push the slider back. This also opens the mouthpiece hole. It is important to keep the inhaler horizontal.

 

INHALING:

3: Now the blister is open, fully breathe out before bringing the device to the mouth.

4: Put your lips around the mouthpiece, taking a long deep breath in.

5: Following this, hold your breath for 10 seconds.

6: Breathe out and breathe normally.

 

CLOSING:

7: After use, bring the slider forward. There is a ratchet mechanism that ensures the holding wheel can only turn a desired distance in one direction.

8: If the user hasn’t fully brought the slider forward, by closing the cover the device is fully reset for when the cover is next opened.

 

What is the Diskus made of?

So, for these simple steps to be enabled, what are the individual components that enable the operation of the Diskus? We conducted a teardown to isolate the individual components – it is copied at the end of this blog. Here is a summary of our findings:

The device is a clever take on how to locate, pierce and remove a measured dose from a blister tape roll. The components are carefully selected, and the minimum material required to perform each mechanical step is used. Although it looks complex at first, the device is well optimised. The assembly steps are repeatable and fairly simple.

There are plenty of other ways that DPI inhalers can function, and this is vastly explored in the current inhalation landscape. However, due to its simplicity and how the repeatability of the same action is controlled, you can certainly see why 1 billion have been made and why the device has been around for 20 years!

A consideration that might improve the device is the knowledge that you must hold it horizontally. If the device could be used in any orientation, the robustness would be further improved.

The largest room for improvement is environmentally. Although a low number of materials are used, due to there being different types of plastic, the inhaler cannot be recycled without disassembly. It is likely just thrown in general waste by users once the total doses are taken.

From this teardown, we have recognised that there are ways that the device’s life cycle could be made circular. The smallest change to the device would be to create a take back scheme – many of the parts could comfortably be used again; following a sterilization operation, a new sealed tape could be inserted, and the device resold. That being said, industry has found that return rates in take-back scheme trials are extremely low. Additionally, can reuse be commercially competitive in transport, cleaning and component cost and time than making a new device?

If reuse is the aim, offering a new way for the user to replenish spent tape and automatically reset the counter would be an essential change. The industry certainly sees the benefits of developing effective DPIs as the future. Budget and growth resource for DPIs is set to continue to grow considerably against MDI’s over the next few years.

THE TEARDOWN:

The Diskus is a cleverly designed inhaler – we hope that this breakdown of the device has been insightful. Please get in touch to discuss how Haughton Design can help with your drug delivery device design & development.

Robert Garland - Medical Device Design Development Engineer at Haughton Design Rob Garland 12 May 2023

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Get in Touch with Rob Garland

Design Development Engineer

Rob graduated from the Dyson School of Design Engineering at Imperial College London in 2021 with a Master’s in Design Engineering. Prior to joining HD, he worked in the automotive sector using state of the art 3D scanning and 3D printing techniques. He has a keen interest in human centred, interaction and experience design and has expertise in additive manufacturing, CAD, IoT, UI and mechatronics.

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