Inexpensive and Easy-To-Use Alternative to the Die Holder for Pharmacopoeial Intrinsic Dissolution Tests

The pharmacopoeial test method "Intrinsic Dissolution" (Ph.Eur. 2.9.29) is used to study the rate of dissolution for powders of active pharmaceutical ingredients normalized by the surface area. Therefore, powders are compacted into a special metal die holder, which is immersed into a dissolution vessel of the dissolution test apparatus (described in Ph.Eur. 2.9.3). However, in some cases, the test cannot be performed because the compacted powder would not stay in the die holder when in contact with the dissolution medium. In this study, we investigated the removable adhesive gum (RAG) as an alternative to the official die holder. Intrinsic dissolution tests were carried out to exemplify the use of the RAG for this purpose. As model substances, acyclovir and its co-crystal with glutaric acid were used. The RAG was validated for compatibility, release of extractables, unspecific adsorption and the ability to block drug release through the covered surfaces. The results showed that the RAG leaked no unwanted substances, showed no adsorption of acyclovir and blocked its release from covered surfaces. The intrinsic dissolution tests revealed, as expected, a constant release of drug with a small standard deviation between replicates. It was possible to distinguish the acyclovir release from the co-crystal and from the pure drug compound. In conclusion, the findings of this study suggest to consider removable adhesive gum as an easy-to-use and inexpensive alternative to the compendial die holder in intrinsic dissolution tests.