To Maintain Formulation Composition Similarity of Coated Tablets of Different Strengths: Should Coating be Based on Core Tablet Weight or Surface Area?

Purpose: As per the Japanese or SUPAC guidance to maintain formulation composition similarity across tablet strengths, the coating should be applied based on the core tablet surface area or weight, respectively. These two coating approaches were compared by evaluating protective effects of coating on the light stability of three model compounds.

Methods: Core tablets of three light sensitive drugs, nifedipine, rosuvastatin calcium, and montelukast sodium were coated either with PVA-based Opadry® II white or Opadry® II beige. The coated tablets were exposed to light up to three ICH cycles.

Results: For Opadry® II white, the surface area based coating provided consistent light protection across tablet strengths when the coating amount was more than 0.1 mg/mm compared to that based on core tablet weights. For Opadry® II beige, both approaches gave comparable and better light protection due to presence of iron oxides. The light protection by Opadry® II white could be because of physical barrier of coating, which was uniform across the strengths when it was based on core tablet surface area.

Conclusion: For a routine tablet formulation development with Opadry color coating, it does not matter whether the coating is applied based on the core tablet surface area or weight.