Methodology to estimate the break force of pharmaceutical tablets with curved faces under diametrical compression

This paper develops a methodology to estimate the break force of curved faced tablets under diametrical compression. Common excipients used in pharmaceutical tablet formulations, including microcrystalline cellulose, calcium phosphate and mannitol as well as their mixtures were characterised. Compacts of different densities were manufactured and their compressive and tensile strength was measured. The break force of curved face tablets having a comprehensive range of face curvatures and thickness was measured using the diametrical compression method ("hardness" test). Equation σ_d=FπD²atD+bWD^-1 introduced by Shang et al. (2013) was used to relate the break force (F) to tablet geometry (D, t, W) and material tensile strength (σ_d). Here, we propose a method to estimate the parameters a and b using data for flat faced tablets. The method was validated for four mixtures. The errors were analysed and compared with the USP29 method σ_d=10FπD²(2.84(t/D)-0.126t/W+3.15(W/D)+0.01)^-1. The proposed method has better accuracy, however, requires additional characterisation of the compressive strength of the material.