Terahertz alternative for wet dissolution testing

Terahertz imaging may become a viable replacement for wet dissolution testing, according to a new US Food and Drug Administration study.

The study claims that better prediction and control of drug release can be achieved by using terahertz imaging to map tablet coating thickness and density.

The benefits of terahertz through accelerated product development, de-risked and rapid scale up into manufacture and maintenance of in-spec products is further endorsed by a recent study conducted by the Universities of Duesseldorf and Otago.

Terahertz imaging was used to map the coating thickness, in the FDA publication, and mean dissolution times were found to correlate with the average tablet coating thickness. This suggested that the coating thickness played a significant role in product design and performance.

This recent study has now identified that to get a better predictor and monitor of dissolution characteristics; coating thickness should be measured in combination with coating density.

The Duesseldorf /Otago research has demonstrated the ability of terahertz imaging to measure and map coating density across the surface of a tablet. The research also showed that for some coatings, particularly those that act as semi-permeable membranes, density of the coating can be a more powerful indicator of dissolution time than coating thickness, which does not take in to account the porosity of the coating that may result from non-optimised coating conditions.

The research also provides a key performance indicator that can be used to more successfully scale-up a sustained release product than the usual non-direct measurement of weight gain.

Modified release coatings can be difficult to scale-up due to the need to change process parameters as well as batch size. Until the development of terahertz pulsed imaging (TPI) by Cambridge-based UK companyTeraView, there has not been a method to directly and non-destructively assess the impact of changing process conditions on coating critical quality attributes such as coating thickness, density and porosity, and establish the uniformity of these across the tablet surface.

TeraView ceo Dr Don Arnone, said: "This study reinforces the use of terahertz solutions to address issues in solid dosage form development. Its successful application in the scale up of modified release coatings is unique and not replicated by any other existing techniques."

He added: "These capabilities deliver significant business benefits for our customers through accelerated development of new products, as well as helping to ensure that these products remain in-spec and compliant once they are on the market."

This study is due to be published in the Journal of Controlled Release in April 2008 (Volume 127, Issue 1, 7 April, pages 79-87).