Evaluation of coating properties of enteric-coated tablets using terahertz pulsed imaging.

PURPOSE: Enteric coatings are used to reduce gastrointestinal side effects and control the release properties of oral medications. Although widely used, the effect of formulation and process conditions on physicochemical and functional properties of enteric coatings remains unclear. METHODS: Terahertz pulsed imaging (TPI) was employed to evaluate the coat properties of enteric coated tablets (ECTs) with various acid resistance. Other analytic methods, such as loss on drying, scanning electron microscopy and X-ray computed tomography were then used to validate the relationships established among 4 TPI-derived parameters and the physicochemical properties of enteric coatings. RESULTS: Weight gain measurement did not provide any information to assess acid resistance of enteric coating, whereas four TPI-derived parameters non-destructively reflected the coating properties such as thickness, coat uniformity, density, and water distribution, allowing the identification of the causes of poor acid resistance in certain ECT batches using a single measurement. These parameters also revealed the effect of coating conditions; in particular, coating under dry conditions led to less dense and nonuniform coatings with poor acid resistance. CONCLUSION: We demonstrated the utility of TPI to identify structural defects within ECTs with poor acid resistance. TPI-derived parameters can aid in formulation development and quality control of ECTs.

Quantitative analysis of visible surface defect risk in tablets during film coating using terahertz pulsed imaging.

Tablets are the most common form of solid oral dosage produced by pharmaceutical industries. There are several challenges to successful and consistent tablet manufacturing. One well-known quality issue is visible surface defects, which generally occur due to insufficient physical strength, causing breakage or abrasion during processing, packaging, or shipping. Techniques that allow quantitative evaluation of surface strength and the risk of surface defect would greatly aid in quality control. Here terahertz pulsed imaging (TPI) was employed to evaluate the surface properties of core tablets with visible surface defects of varying severity after film coating. Other analytical methods, such as tensile strength measurements, friability testing, and scanning electron microscopy (SEM), were used to validate TPI results. Tensile strength and friability provided no information on visible surface defect risk, whereas the TPI-derived unique parameter terahertz electric field peak strength (TEFPS) provided spatial distribution of surface density/roughness information on core tablets, which helped in estimating tablet abrasion risk prior to film coating and predicting the location of the defects. TPI also revealed the relationship between surface strength and blending condition and is a nondestructive, quantitative approach to aid formulation development and quality control that can reduce visible surface defect risk in tablets.

Quantitative analysis of the layer separation risk in bilayer tablets using terahertz pulsed imaging.

Layer separation is a critical defect in many bilayer tablets. Despite its importance for product quality, few studies have investigated its root cause. We evaluated bilayer tablets with varying layer separation tendencies using terahertz pulsed imaging (TPI) in comparison with other analytical methods such as tensile strength measurements, friability testing, scanning electron microscopy (SEM), and X-ray computed tomography (XRCT). The layer separation risk was determined by friability testing and shown to be correlated with the final compression pressure used for bilayer tablet fabrication. TPI could nondestructively detect cracks between the component layers that lead to layer separation. The adhesion integrity of the interface was quantified by the interface index, a unique value derived from the time-domain terahertz waveform. The interface index showed good correlation to the layer separation tendency and could distinguish interface quality among seven batches of bilayer tablets. In contrast, SEM and XRCT detected structural defects but could not distinguish batches with high or low layer separation risk. TPI revealed the relationship between compression pressure and interface quality. Thus, TPI can aid in quality control by providing a precise estimate of the layer separation risk and robust quality of bilayer tablet development with better understanding of layer separation.