Formulating minitabs – a study of SmartEx™ – a cellulose derivative

Summary

The study of the behaviour of the Orodispersant excipient was successful as a wide range of compaction forces yielded tablets of good tensile strength. Most of the tablets made disintegrated within the required 30 seconds duration except for those made using 2.5kN (250kg or 330MPa) force. This means that the excipient will positively influence solid dosage formulation.

Introduction

Laboratory-based compaction studies are difficult to perform because of the lack of suitable equipment. All tablet properties are determined by the compaction pressure used to make the tablets, but most companies cannot measure this parameter. The Gamlen Tablet Press was designed to enable the compaction of tablets in the laboratory using controlled compaction force. This enables the development of products in a scientific way.

Critical Quality Attributes (CQAs) of a tablet requires measurements made under controlled compaction pressure.  Tablet CQAs include:

a) Tensile Fracture Strength (TFS)
b) Solid fraction
c) Friability of the compact
d) Disintegration
e) Dissolution (if needed)

Any proper formulation study should include objective measurement of these parameters in a controlled testing system. The relationship between TFS and compaction pressure is a fundamental relationship which is characteristic of the formulation or material and has been shown to extrapolate to compaction behaviour under production, enabling reliable predictions of production behaviour to be made on the basis of a simple laboratory test.

Methodology

We used the Gamlen Tablet Press to evaluate the effect of compaction pressure on the CQAs of Oral Disintegrating Tablets (ODTs) prepared from Shin Etsu’s SmartEx™.  Dissolution testing is not a CQA for ODTs, but all other parameters listed were measured.  The methodology included:

  • Blending of formulation with a lubricant (1% MgStearate) for 3 minutes using a WAB TURBULA mixer.
  • Weighing out 25mg of the resulting mixture and tableting using various compaction forces, we recorded Compaction, Detachment and Ejection forces for 3mm tablets each weighing 25mg.
  • Full characterisation of the compact which includes measurements of weight, thickness, diameter and hardness.
  • Comparison of the disintegration times of the compacts in respect of varying compaction forces.
  • Friability testing.

Tensile Strength

The Tensile Strength of a tablet can be defined as, the force required to break a compact or tablet in tension. It is normally measured by applying a diametral load to a flat-faced tablet and measuring the peak force required to break the tablet. The tablet TFS is calculated from the breaking load using the formula of Fell and Newton, which takes into account tablet dimensions (diameter and thickness).

Figure 1 below shows the effect of compaction pressure on the tablet TFS of SmartEx™ QD-50 tablets. This is generally a linear relationship until high solid fractions – the higher the compaction pressure the stronger the tablet. This provides a simple and objective way to compare tablet formulations and processes.

 

 

 

 

 

 

 

 

 

 

Figure 1 Tensile fracture stress (MPa) vs Compaction pressure (MPa) plots for SmartEx™

 

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