We've updated our Privacy Policy to make it clearer how we use your personal data. We use cookies to provide you with a better experience. You can read our Cookie Policy here.


Bringing the Beauty of Dissolution to the World of Medical Devices

Person inserting a contact lens.
Credit: iStock.
Listen with
Register for free to listen to this article
Thank you. Listen to this article using the player above.

Want to listen to this article for FREE?

Complete the form below to unlock access to ALL audio articles.

Read time: 3 minutes

When you get a headache, you want something that delivers immediate relief. When pollen levels spike, sufferers want an allergy medication that works all day. These types of products are designed to provide a consistent therapeutic effect, batch after batch. Importantly, every batch requires a dissolution test to verify their efficacy.

However, products coated with a small amount of drug that releases over an extended period of time aren’t suitable for traditional instrumentation. Therefore, novel drug delivery mechanisms and devices require a new approach to this regulated technique. So how can the developer – and eventually the manufacturer – ensure these types of products are serving their purpose in the highly regulated pharmaceutical world?

Dissolution testing is commonly used for tablets and capsules to measure the release rate of an active pharmaceutical ingredient (API) into a solution. It’s used at nearly every stage of the drug development process, most often as a quality control mechanism to ensure product efficacy. As delivery systems continue to evolve, the established techniques defined in the United States Pharmacopeia (USP), European Pharmacopoeia (EP) and other harmonized regulatory agencies, aren’t always suitable without some sort of modification. This is true for combination products – the combination of a drug and a device – and certainly applies to many medical devices currently on the market.

So how can we turn this advanced dissolution technology and apparatus, traditionally used for our headache and allergy pills, to medical devices with API’s, such as drug-eluting stents or medicated contact lenses?

These devices are typically coated with a much smaller amount of API, which is released over the duration of days, weeks or even months; yet it remains critically important to be able to quantify drug release over time to ensure proper manufacturing of each batch as well as product safety.

Spotlight on USP Apparatus 7 (reciprocating holder)

Of the seven dissolution apparatus types defined in the USP general chapters <711> Dissolution and <724> Drug Release , the last of this grouping, USP Apparatus 7, doesn’t always get the most attention. As mentioned previously, most dissolution is performed on tablets and/or capsules using USP apparatus 1 (baskets) or 2 (paddles) in a 1-liter vessel. When it comes to medical products with considerably less API and a much longer release period, method developers will soon run into problems using these techniques. That is why USP Apparatus 7 – officially called the reciprocating holder – is a useful place to start.

The reciprocating holder lends itself to easily reducing the vessel volume, therefore increasing the concentration, and making quantification of API more achievable. It is a solution designed to be used when the traditional USP Apparatus 1,2 or 3 don’t work for the drug delivery system being tested. Defined in the USP, various sample holders, such as acrylic rods, various baskets and stent holders, can support a variety of products.

Due to the reduced volume and extensive length of the dissolution tests for these products, evaporation control is another key factor that must be considered. Traditional evaporation covers are usually inadequate, so a design to incorporate a sealed sample cell or vessel is preferred. This guarantees that the volume is maintained, and evaporative loss isn’t adversely affecting your test results. Lastly, systems capable of automated sample collection are of great value for tests that may only require one sample per day.

A dissolution solution for medical devices

In the past, scientists were struggling to find the solution they needed for their analysis of drug-eluting stents or medical devices, to the point where they were using homemade solutions in the form of capped shaker bottles and the like.

We saw this as a challenge and set about developing a very specialist piece of equipment called the Agilent 400-DS. Originally designed for stent analysis, this instrument can now achieve the characteristics required for successful dissolution testing of a variety of drug-coated medical devices, from ocular implants and contact lenses to vaginal rings, suspensions, mini-tablets and nasal sponges.

This instrument combines adherence to USP Apparatus 7 guidelines with enhancements specifically designed to accommodate long-term tests using advanced reciprocation and evaporation control, automated sampling and electronic data compliance. This makes it easier for labs to meet regulatory compliance and take the product all the way from design to QC. As the trend of novel drug development continues, especially in the medical device space, we need to carry on innovating to meet the creative challenges and individual requirements of each device.

About the author

Headshot of Dan Spisak
Dan Spisak joined the dissolution business in 2001 as a field service engineer. Since then, he has held the roles of validation chemist, product specialist, account manager and most recently product manager from 2010 to June 2020.  
From June 2020, Dan has led the creation of the expanded team and Dissolution Center of Excellence at the Craven Arms site in the UK as marketing manager.

With nearly 20 years of experience in dissolution instrumentation, automation, qualification and compliance, Dan offers valuable insights on how the Agilent solutions meet the requirements set forth by regulatory agencies and ensure these standards are fulfilled.

Dan is passionate about creating effective strategies and successfully communicating this messaging to the Agilent worldwide teams as well as end users. He is also adept at gauging his audience and delivering the necessary information in an easily digestible format. 
Dan holds a Bachelor of Science degree in biochemistry from Lehigh University in Bethlehem, PA, USA.