Determining the effect of photodegradation on film coated nifedipine tablets with terahertz based coating thickness measurements

Exploring Immersion Coating as a Cost-Effective Method for Small-Scale Production of Enteric-Coated Gelatin Capsules

The coating process for solid dosage forms is widely used in the pharmaceutical industry but presents challenges for small-scale production, needed in personalized medicine and clinical or galenic settings. This study aimed to evaluate immersion coating, a cost-effective small-scale method, for enteric-coated gelatin capsules using standard equipment. Two enteric coating polymers and different polymer concentrations were tested, along with API solubility. Results were compared with commercially available enteric capsule shells. Successful preparation of enteric coating capsules via immersion necessitates a comprehensive grasp of API and enteric polymer behavior. However, utilizing commercially available enteric capsule shells does not guarantee ease or robustness, as their efficacy hinges on the attributes of the active ingredient and excipients. Notably, coating with Eudragit S100 stands out for its superior process robustness, requiring minimal or no development time, thus representing the best option for small-scale enteric capsule production.

Evaluating Spatially Offset Low-Frequency Anti-Stokes Raman Spectroscopy (SOLFARS) for Detecting Subsurface Composition below an Emissive Layer: A Proof of Principle Study Using a Model Bilayer System

This work explores the potential use of spatially offset low-frequency anti-Stokes Raman spectroscopy (SOLFARS) to detect subsurface composition below an emissive surface. A range of bilayer tablets were used to evaluate this approach. Bilayer tablets differed in both the underlying layer composition (active pharmaceutical ingredient to excipient ratio, celecoxib: α-lactose monohydrate) and the upper layer thickness of the fluorescent coating (polyvinylpyrrolidone mixture with sunset yellow FCF dye). Two low- (<300 cm^-1) plus mid- (300 to 1800 cm^-1) frequency Raman instrumental setups, with lateral displacements for spatial analysis of solid dosage forms, using different excitation wavelengths were explored. The 532 nm system was used to illustrate how the low-frequency anti-Stokes Raman approach works with samples exhibiting extreme fluorescence/background emission interference, and the 785 nm system was used to demonstrate the performance when less extreme fluorescence/emission is present. Qualitative and quantitative chemometric analyses were performed to evaluate the performance of individual spectral domains and their combinations for the determination of the composition of the subsurface layer as well as the coating layer thickness. Overall, the commonly used midfrequency region (300-1800 cm^-1) proved superior when using 785 nm incident laser for quantifying the coating thickness (amorphous materials), whereas a combined Stokes and anti-Stokes low-frequency region was found to be superior for quantifying underlying crystalline materials. When exploring individual spectral regions for subsurface composition using spatially offset measurements, the anti-Stokes LFR spectral window performed best. The anti-Stokes low-frequency range also demonstrated an advantage for models composed of data exhibiting high levels of fluorescence (e.g., data collected using 532 nm incident laser), as the Stokes scattering was masked by fluorescence. Transmission measurements were also explored for comparison and showed the best applicability for both upper and lower layer analysis, attributed to the inherently larger bulk sampling volume of this setup. From a practical perspective, these results highlight the potential adjustments that can be made to already existing (in-line) Raman setups to facilitate similar analysis in pharmaceutical industry-based settings.

Evaluation of coating uniformity for the digestion-aid tablets by portable near-infrared spectroscopy

Process analysis can effectively stabilize pharmaceutical quality and optimize the control of production process. For the sustained-release digestion-aid tablets, the coating film thickness is an important indicator to measure the quality of products. Traditional method mainly spot-checks tablets and measures with visual microscopy, which is time-consuming and laborious. This study attempted to use a portable near-infrared spectroscopy for rapid detection of a Chinese medicine tablets from production line. First, PLS regression models were established for coating film at twelve different locations of the tablet section, and the results showed that the correlation coefficients of training and validation sets were all over 0.80. Subsequently, the twelve locations were divided into six groups to further establish regressions. After chemometrics optimization, the optimal of six group models were generally better than single location models, with R_c² and R_v² all above 0.85, and RMSEV values all below 2.0. The mean relative error of prediction of the optimal model was 9.49%. The pharmaceutical process detection based on the portable NIR spectroscopy met the demand of managing digestion-aid tablet coating data conveniently. The proposed approach can successfully realize on-site and online pharmaceutical monitoring and has a promising practical value.

Visualising liquid transport through coated pharmaceutical tablets using Terahertz pulsed imaging

Dissolution of pharmaceutical tablets is a complex process, especially for coated tablets where layered structures form an additional barrier for liquid transport into the porous tablet matrix. A better understanding of the role of the coating structure in the mass transport processes that govern drug release, starting with the wetting of the coating layer by the dissolution medium, can benefit the formulation design and optimisation of the production. For this study, terahertz pulsed imaging was used to investigate how dissolution medium can penetrate coated tablets. In order to focus on the fundamental process, the model system for this proof-of-principle study consisted of tablet cores made from pure microcrystalline cellulose compacted to a defined porosity coated with Opadry II, a PVA-based immediate release coating blend. The coating was applied to a single side of flat-faced tablets using vacuum compression moulding. It was possible to resolve the hydration of the coating layer and the subsequent liquid ingress into the dry tablet core. The analysis revealed a discontinuity in density at the interface between coating and core, where coating polymer could enter the pore space at the immediate surface of the tablet cores during the coating process. This structure affected the liquid transport of the dissolution medium into the core. We found evidence for the formation of a gel layer upon hydration of the coating polymer. The porosity of the tablet core impacted the quality of coating and thus affected its dissolution performance (r =  0.6932 for the effective liquid penetration rate RP_eff and the core porosity). This study established a methodology and can facilitate a more in-depth understanding of the role of coating on tablet dissolution.

Pharmaceutical Application of Tablet Film Coating

Tablet film coating is a common but critical process providing various functionalities to tablets, thereby meeting diverse clinical needs and increasing the value of oral solid dosage forms. Tablet film coating is a technology-driven process and the evolution of coated dosage forms relies on advancements in coating technology, equipment, analytical techniques, and coating materials. Although multiple coating techniques are developed for solvent-based or solvent-free coating processes, each method has advantages and disadvantages that may require continuous technical refinement. In the film coating process, intra- and inter-batch coating uniformity of tablets is critical to ensure the quality of the final product, especially for active film coating containing active pharmaceutical ingredients in the coating layer. In addition to experimental evaluation, computational modeling is also actively pursued to predict the influence of operation parameters on the quality of the final product and optimize process variables of tablet film coating. The concerted efforts of experiments and computational modeling can save time and cost in optimizing the tablet coating process. This review provides a brief overview of tablet film coating technology and modeling approaches with a focus on recent advancements in pharmaceutical applications.

Application of Process Analytical Technology for Pharmaceutical Coating: Challenges, Pitfalls, and Trends

Coating process is a critical unit operation for manufacturing solid oral dosage forms. For a long time, the coating weight gain has been discerned as the most important, if not only, characteristic describing the coating quality. As the introduction of quality by design (QbD) and advancement of process analytical technology (PAT), nowadays more techniques are available to analyze other quality attributes which have been overlooked but have substantial impacts on the performance of coated products. The techniques that permit rapid and non-destructive measurements are of particular importance to improve process operation and product quality. This article reviews the analytical techniques that have been and potentially could be used as PAT tools for characterizing the quality of pharmaceutical coating product. By identifying the challenges and pitfalls encountered during PAT application, the review aims at fostering the adoption of PAT for paving the way to enhanced quality and efficiency of the coating processes.

Terahertz Time of Flight Spectroscopy as a Coating Thickness Reference Method for Partial Least Squares Near Infrared Spectroscopy Models

Near infrared spectroscopy (NIRS) is often used during the tablet coating process to assess coating thickness. As the coating process proceeds, the increase and decrease in NIRS signal from both the coating formulation and tablet core has been related to coating thickness. Partial least-squares models are often generated relating NIRS spectra to reference coating thickness measurements for in-line and/or at-line monitoring of the coating process. This study investigated the effect of the reference coating thickness measurements on the accuracy of the model. The two primary reference techniques used were weight gain-based coating thickness and terahertz-based coating thickness. Most NIRS coating thickness models currently use weight gain-based reference values; however, terahertz-time-of-flight spectroscopy (THz-TOF) offers a more direct reference coating thickness measurement. Results showed that the accuracy of the NIRS coating thickness model significantly improved when terahertz-based coating thickness measurements were used as reference when compared to weight gain-based coating thickness measurements. Therefore, the application of THz-TOF as a reference method is further demonstrated.