Colorcon Ltd.

While designed for rapid drug release, immediate release (IR) film coatings can transiently impede water transport, affecting tablet hydration. The impact of coating density and thickness on hydration kinetics was investigated using polyvinyl-alcohol-based Opadry II coatings on placebo tablets. By manipulating coating parameters during spray application, tablets with varying film attributes were created. A direct correlation between refractive index and coating density was revealed by terahertz surface reflection. It was demonstrated by terahertz pulsed imaging that both coating density and thickness significantly influence hydration and dissolution rates, with density proven as a more promising factor than weight gain alone. The importance of coating parameter control to ensure predictable tablet disintegration and drug release is underscored, with coating density highlighted as a key determinant.

Pharmaceutical tablets are routinely film-coated to improve appearance, reduce medication errors and enhance storage stability. Terahertz pulsed imaging (TPI) can be utilised to study the liquid penetration into the porous tablet matrix in real time. Using polymer-coated flat-faced tablets with anhydrous lactose or mannitol, we show that when the tablet matrix contains anhydrous material, the anhydrous form transforms to the solid-state hydrate form in the tablet core while the immediate release coating dissolves. The process starts at the interface between the coating and the core. It commences inward for more than 7min, resulting in a shell of hydrate form on the order of a few hundred microns thicknesses immediately underneath the dissolving coating. TPI is sensitive enough to detect and spatially resolve this process based on the subtle change in the refractive index of the two materials. TPI can further resolve tablets with different components using the time-domain waveforms in reflection and provide insights into the presence of hydrate material (lactose monohydrate) in altering the water mass transport mechanism. The kinetics data obtained from TPI fit the power law model (y=kt^m), whose constants enable us to infer the different mass transport mechanisms.

Coated tablets introduce complexity to the dissolution process, even with readily soluble immediate release coating layers. Therefore, a more detailed understanding of the physical steps involved in the dissolution process can improve the efficiency of formulation and process design. The current study uses terahertz pulsed imaging to visualise the hydration process of microcrystalline cellulose (MCC) tablet cores that were film coated with an immediate release coating formulation upon exposure to the dissolution medium. Film coated tablets that were prepared from three levels of core porosity (10%, 20% and 30%) and with coating thickness in the range of 30μm to 250μm were investigated. It was possible to resolve and quantify the distinct stages of wetting of the coating layer, swelling of the MCC particles at the core surface, and dissolution of the coating layer followed by the ingress of dissolution media into the tablet core. The liquid transport process through the coating layer was highly consistent and scalable. The penetration rate through the coating layer and the tablet core both strongly depended on coating thickness and core porosity.