Many medicinal tablets are coated to improve in-vivo performance. Coatings are used to mask the taste of active pharmaceutical ingredients (APIs) and to control the location and rate of dissolution, to aid uptake, reduce side effects or prolong action via controlled release. As a result, coating integrity and thickness may be Critical Quality Attributes (CQA) for tablets. A coating must consistently cover the whole tablet and be sufficiently thick to transport the API safely to the intended site of action, but not so thick that the tablet passes through the site of action without dissolving. Being able to rapidly and reliably measure and control coating integrity is therefore crucial.
This application note describes a study in which the Micromeritics® AccuPyc II gas pycnometer and the Micromeritics® GeoPyc envelope density analyzer were used to compare the characteristics of coated and uncoated tablets. These instruments measure skeletal volume and envelope volume, respectively, this data combined with a supplied sample mass can generate four parameters, which are: skeletal and envelope density and the sample’s porosity. The porosity value can also be used to determine solid fraction and is simply [(100 – porosity) / 100]. This terminology is discussed further in the “Physical Properties Primer” below.
The results from this study highlight how skeletal density and porosity are impacted by scratching and splitting tablets, and how they can be used to assess coating quality. The data illustrate the potential and value of using these two measurements for monitoring coating processes.
Many medicinal tablets are coated to improve in-vivo performance. Coatings are used to mask the taste of active pharmaceutical ingredients (APIs) and to control the location and rate of dissolution, to aid uptake, reduce side effects or prolong action via controlled release. As a result, coating integrity and thickness may be Critical Quality Attributes (CQA) for tablets. A coating must consistently cover the whole tablet and be sufficiently thick to transport the API safely to the intended site of action, but not so thick that the tablet passes through the site of action without dissolving. Being able to rapidly and reliably measure and control coating integrity is therefore crucial.
This application note describes a study in which the Micromeritics® AccuPyc II gas pycnometer and the Micromeritics® GeoPyc envelope density analyzer were used to compare the characteristics of coated and uncoated tablets. These instruments measure skeletal volume and envelope volume, respectively, this data combined with a supplied sample mass can generate four parameters, which are: skeletal and envelope density and the sample’s porosity. The porosity value can also be used to determine solid fraction and is simply [(100 – porosity) / 100]. This terminology is discussed further in the “Physical Properties Primer” below.
The results from this study highlight how skeletal density and porosity are impacted by scratching and splitting tablets, and how they can be used to assess coating quality. The data illustrate the potential and value of using these two measurements for monitoring coating processes.
The AccuPyc is a gas pycnometer, it works by having two chambers: a sample chamber and an expansion chamber, both with carefully calibrated volumes. A sample is loaded into the sample chamber and pressurized through valve a, the equilibrated pressure is then recorded using the transducer t. The gas is then expanded through valve B to the expansion chamber, where the equilibrated pressure is again recorded. Using the ideal gas law, the volume occupied by the sample can be calculated from the known volume of the chambers and measured pressure values. The volume measured is the skeletal volume of the sample, since gas penetrates all accessible pore space.
Please download to read more.