Compactibility of mixtures of calcium carbonate and microcrystalline cellulose

Abstract

A patented coprocessed mixture of microcrystalline cellulose (MC) and calcium carbonate (CC) is claimed to perform, as a pharmaceutical excipient, equal or better than pure MC. To investigate it, the tensile strength ( T) of tablets made of mixtures of MC type 102, CC, magnesium stearate (MS) and polyvinylpyrrolidone (PVP) and formed under a compaction pressure ( P c) ranging up to 618 MPa has been determined. The compactibility of the mixtures was defined through regression parameters obtained with ln(−ln(1− T/ T max))=slope×ln P c+intercept. MC/CC mixtures, P c=618 MPa, show a small decrease in tablet tensile strength with CC proportions up to about 20%, falling considerably thereafter. Lower compaction pressures, P c≤332 MPa, show a continuous decrease in tensile strength as the CC proportion increases. A MC drastic fall in tablet tensile strength due to 2%-MS, P c=487 MPa, was recovered to 35% of its original value admixing about 25% CC. This maximal value of recovery showed a shift to lower proportions of CC, up to 10%, as compaction pressure decreased. This was attributed to lower CC-particles fragmentation or agglomerates spreading at lower compaction pressures. Mixtures with increased plasticity (MC/CC/PVP and MC/CC/PVP/MS) showed an increased compactibility, which was more evident at higher compaction pressures and higher CC proportions, presumably due to higher deformation and erosion of PVP particles. Inclusion of about 40% CC in a MC/PVP/MS mixture showed 60% recovery of the original MC tablet tensile strength. Lower MS proportions are expected to allow a higher recovery.