Table Testing Techniques

The rising popularity of fast dissolving, immediate-release dosage forms can be attributed to their convenience and ease of administration. Although particularly applicable to the paediatric and geriatric markets, fast-melting tablets (FMTs) are suitable for consumers of all ages. To ensure reliable and consistent drug release, however, formulators must conduct a thorough disintegration analysis, as the tablet has to be resilient enough to endure manufacturing and shipping, but must also disintegrate sufficiently to provide an optimum dissolution rate.

Jo Smewing

The traditional and most commonplace method employed by researchers to assess dissolution properties involves submerging a tablet, which was attached with tape to the bottom of a cylinder probe, and then testing the time required for the tablet to dissolve. However, because the tablet is 'trapped' between the tape and the vessel base, its exposure to the medium is restricted. To more accurately examine water absorption and the disintegration of associated particles into individual components, it is important to replicate the conditions of the human mouth as closely as possible in vivo.

One innovative solution is to use a tablet disintegration rig, which enables the disintegration medium to access the tablet from all areas. The dry tablet sample is secured to a probe by a thin strip of double-sided adhesive tape along its diameter. The probe's surface has a channelled design that enables the fluid to flow freely all round the tablet, while ensuring that contact is maintained with the probe. Once the probe is lowered into the medium, the tablet is positioned on a perforated platform and a constant force is applied to it. The perforated surface enables free ingress of fluid beneath the sample and subsequent dispersion of the disintegrant. The rig allows the FMT particles to detach easily during the disintegration process, imitating the realistic conditions of drug administration and providing more accurate analysis regarding performance and efficiency.

When designing fast melting tablets, the use of tablet film coatings has become a popular practice because such films fulfil multiple roles, from aesthetics and taste or odour masking, to eased ingestion and prolonged product shelf life. Problematically, on the other hand, aqueous film coatings also tend to act as local stress concentrators that promote cracking, edge splitting and peeling. A technique called texture analysis (see sidebar) is commonly used to investigate the response of a tablet in situations that mimic its actual usage. Such analysis can measure the adhesiveness, rupture, burst strength, resilience and relaxation properties of pharmaceutical film coatings. The results of texture analysis will help manufacturers to optimise their formulations and manufacturing processes to avoid potential issues.

Texture analysis

Bi-layer tablet boom

Recently, bi-layer dosage forms have witnessed a boom in popularity, which can be attributed to the added efficacy over time that they offer. Because of this unique characteristic, bi-layer tablets are often used to provide a combination of immediate-release dose for fast-acting relief and a dose of controlled-release to maintain the therapeutic effect. Not surprisingly, these tablets are also prone to a number of qualitative issues such as layer separation, insufficient hardness, inaccurate individual layer weight control and cross-contamination between the layers. To avoid these pitfalls, manufacturers have to assess the physical characteristics of high-load APIs, which usually require bespoke manufacturing formulations to overcome barriers, such as low melting points or poor compressibility. Innovative texture analysis methodologies mean these quality issues can be accurately evaluated by analysing physical properties in conditions that closely resemble in vivo conditions

Separation of the two individual layers in a bi-layer tablet is a common problem and one that significantly impacts the quality and efficacy of the medication. It is the consequence of insufficient bonding between the two layers during final compression of the tablet. However, this issue can be mitigated using systems and technologies that assess the force required to separate the layers of a bi-layer tablet. This allows manufacturers to identify exactly why tablets are failing, and to subsequently take corrective action quickly and effectively.

Jo Smewing is Applications Manager at Stable Micro Systems Ltd.