Novel device solves inhaler dose counting problem

A novel mechanism has been developed that comprises just five working parts but which accurately counts the number of doses asthma sufferers have inhaled from their asthma inhaler. The device uses a modified ‘Sully escapement mechanism’ used for centuries in clock making. The mechanism was specifically designed for easy, low cost manufacture and can be produced without requiring expensive, high tolerance moulded components or complex assembly processes. And, because the device is so easy to design-in and manufacture, it is hoped that pharmaceutical and medical companies will be able to significantly shorten their development and regulatory approval timescales and cut time-to-market. The mechanism was developed by British product design consultancy firm, 42 Technology based in St Ives, Cambridge. Currently, there are three designs on the drawing board (or ‘Pro/Engineer’ CAD screen) although one design in particular looks like it will be taken up by one of the big pharma companies. Nick Campling, Managing Director at 42 Technology explained the problems associated with most of today’s inhaler devices: “The problem with most current pressurised metered dose inhalers [pMDIs] is that they don’t have a practical way of counting the doses delivered or remaining within the canister. Patients are encouraged to keep a note of how many times they’ve used their inhaler but obviously this is difficult to manage and studies have shown that most patients are very anxious about not knowing how many doses are left. Also, many patients wait until their existing inhaler is exhausted before requesting a new one.” Asthma sufferers are also at risk from over-filling. The aerosol canisters, said Campling, are deliberately over-filled during manufacture to ensure that the device can deliver the labelled number of metered doses and that each dose will include the correct amount of active ingredients. “However, the net result of this,” explained Campling, “is that patients often continue to rely on their inhalers and use them even when they’re ‘officially’ exhausted and the proportion of drug to propellant is reduced. As a result, patients run the risk of getting into a potentially life-threatening situation and then not being able to get the correct dosage of drug from their inhaler.” So, to address these issues and improve patient compliance and help save lives, in March 2003 the Food and Drug Administration (FDA) and the related European regulatory bodies recommended that all manufacturers should incorporate a dose counting mechanism into their new pMDIs. According to Campling, these new devices will need to be able to track actuations reliably; be designed to count down towards zero and prevent under-counting; and allow the device to continue to actuate beyond the number of labelled doses so that patients in a crisis can continue using them if they get into a life-threatening situation and have no alternative to hand. As Campling told Eureka: “Our approach has been to re-visit existing established technologies and to specifically design a low part count solution that was easy to manufacture and where high tolerance components have been designed out. The problem with existing asthma inhalers are that they are based on 50-year old designs. Tolerances were not critical, but when you need to count doses, tolerances become very important. Also, existing inhalers are quite complex assemblies, comprising around 12 to 20 parts. “We’ve developed three devices in all. Two indicators that count every dose and display the number remaining to the nearest 10 doses, rather like a fuel gauge and a numerical counter, which displays the exact number of doses left. All three devices count down from the labelled number of metered doses and, as recommended by the FDA, allow the inhaler to continue to be used even when it is ‘officially’ empty,” said Campling. The Numeric dose counter – which Eureka (and Campling himself) felt was the most promising of the three designs – comprises five working parts (not including the actuator) and is based on a modified ‘Sully Escapement’ mechanism, which has been used for hundreds of years in clock making. The mechanism converts the reciprocating vertical motion of the canister (as patients press the top of the canister for every dose) into rotary motion, counting each dose on a wheel, which records units from ‘0’ to ‘9’. But it also ensures that if the patient does not quite push hard enough on the top of the canister for a single dose, a carefully positioned dog pulls back the Sully mechanism so that the counter remains at the previous recorded number of doses. The canister is attached directly to the dose counter. A second escapement mechanism is used to index a wheel every tenth dose to count tens of doses. A small window on the body of the dose counter displays the number of doses remaining and when the counter reaches zero, the viewing window is covered over to indicate that the inhaler is now ‘officially’ empty. There are two gear wheels, eccentrically-driven, which rotate with each dose. The first gear wheel is numbered 0 to 9 and counts each dose. The second gear wheel is numbered 0 to 20 and counts every 10 doses up to 200 in total. A curiously shaped lever mechanism is attached to the second gear wheel (in green on the video) which rotates but never leaves its central axis, therefore ???????? The really clever thing which 42 Technology has done here, is to adapt existing, widely available technology to create a simple, but highly original solution for a major market opportunity. The other two solutions offered by 42 Technology include a four-part device based on a ‘wobble wheel’ gearing mechanism that completely eliminates the need for high tolerance components and an easy-to-read display wheel is marked into 20 unit divisions, enabling patients to see the number of doses remaining to the nearest 10 doses. The third design incorporates five working parts that use some common tooling using similar components for the numeric dose counter to the favoured ‘Numeric’ dose counter solution. It uses eccentric gearing, rather like a Spiro graph, where there is basically a mis-match between the numbers of gear teeth to create a high ratio gearing mechanism. The result, again, is a solution that comprises a very small number of low tolerance components. All the designs were developed using Pro-Engineer 3D modeling software. All parts are designed in plastic, as this is inexpensive to mould and the device itself needs to survive for only around 200 doses. Campling continued: “Patents have been applied for and we are actively seeking development partners for product development and license deals. We’ve also secured a DTI R&D grant of £50k to further develop the prototypes.” 42 Technology has developed products for all sectors of industry. In the pharmaceutical and medical device sectors, the company has worked for major manufacturers, including AstraZeneca and Bespak. GlaxoSmithKline is currently developing its own dose counting mechanism for asthma inhalers in house. But other inhaler manufacturers need a solution, hence 42 Technology’s current efforts in this area. Aside from novel dose counter mechanisms, 42 Technology has been involved in some very innovative technology projects recently, including a novel drinks dispenser system; friction brake design; the modeling and optimisation of a bore-hole density sensor; domestic boiler developments; gearbox technology evaluation; liquid pumping for aggressive fluids; novel spray dispensing methods; and an innovative cartridge device for diabetes testing.