Evaluating the color stability of titanium dioxide-free film coats under environmental and light stress

Titanium dioxide (TiO₂) is an opacifier/colorant in tablet film coatings and capsule shells. Recently, questions about its safety have raised concerns that it may be banned from medicinal products in the European Union (EU); however, little information exists on alternatives to enable the pharmaceutical industry to pivot. This study evaluated the color stability of film coats containing alternate opacifiers, calcium carbonate (CaCO₃), and rice starch. Placebo tablets were coated with film coating systems containing different polymers (hydroxypropyl methylcellulose (HPMC) or polyvinyl alcohol (PVA)), opacifiers (CaCO₃, rice starch, or TiO₂) and pigments (FD&C Blue No. 2, iron oxides, or non-pigmented); the coated tablets were exposed to environmental stress (temperature/humidity) and light stress and color changes were quantified spectrophotometrically. The HPMC-formulated coats containing CaCO₃ or rice starch showed comparable stability to TiO₂. The PVA-based coats containing FD&C Blue No. 2 or iron oxide colorants exhibited color changes when exposed to elevated temperature/humidity, which was more pronounced with CaCO₃ than with TiO₂. No meaningful color changes were observed under white or UV light stress for any coat. This study demonstrated PVA coating systems pose a stability risk, whereas these alternate opacifiers presented an overall low color stability risk, offering potential TiO₂ alternatives.