(T0930-03-15) How to Ensure a Successful Tablet Coating Formulation Development by Using Polyvinyl Alcohol in Combination with Calcium Carbonate to Provide an Alternative to Titanium Dioxide

Purpose: The European Commission is banning titanium dioxide (TiO2) for the use in food products, as in particular a genotoxicity concern could not be ruled out. The regulation includes a commitment to review the necessity of titanium dioxide as a white colorant in medicinal products. Therefore, it is desired to find a suitable alternative pigment for tablet and pellet coating, that has a comparable covering effect. It is challenging to find a suitable alternative for TiO2 because of its high opacity. As an approved drug colorant in the EU, calcium carbonate provides a potentially safer opportunity in the coating process. Due to its limited opacifying potential the relevant amounts of CaCO₃ need to be identified.

Methods: Colored tablet cores were manufactured using a rotary tablet press (FETTE 1200i) at 74 Upm; compression force: 10kN; height: 5,0 mm; tablet diameter: 11 mm; targeted tablet weight: 500 mg. A simplified core formulation with red iron oxide as pigment was used: 98,0 % mannitol + 0,5 % iron oxide + 1,5% magnesium stearate. The coating with Parteck® COAT (Polyvinyl alcohol) was performed using a rotating drum coater type LDCS from Vector Freund Corporation. To identify a relevant coloring of the core tablets, different concentrations of iron oxide were tested and determined by color measurements.

Results: Based on the results it was found that CaCO3 shows a comparable potential to TiO2 by increasing the solid content in the coating dispersion without any negative effect on the viscosity or feasibility of the coating process in general. Although the effectiveness and efficiency to TiO2 is not directly comparable, the covering effect of CaCO₃ can be enhanced by adapting the solid content of CaCO₃.

Conclusion: The replacement of titanium dioxide by calcium carbonate has a high potential for future coating applications. In combination with polyvinyl alcohol low viscosities of the spraying liquid can be maintained even at high solid contents which can enable a high process efficiency. This effect can potentially balance the required weight gains required to achieve the targeted covering effect of the core tablet surface.


Figure 1: Visual images of tablet surfaces coated with calcium carbonate vs. titanium dioxide.