Jo Smewing
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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.
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.
Texture analysis
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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.
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.
