T. Kalantar, M. Ladika, H. Shao, S. Dean, K. Harris, P. Sheskey, K. Coppens, K. Balwinski, D. Holbrook
Keywords: tablet coating, immediate release, enteric release, quick set latex
Summary:Currently available commercial pharmaceutical tablet coating technology (commonly based on hydroxypropyl methyl cellulose (HPMC), poly (vinyl alcohol) (PVOH)) includes spraying of a dilute polymer solution over the tablets, leading to a time-consuming and high cost drying process. Development of tablet coating technology that minimizes this drying step would be commercially advantageous since it would reduce coating manufacturing time and energy resulting in significant cost savings. In this work, amphoteric latex-based coating materials containing weak acid (WA) and strong base (SB) stabilizing moieties which exist as a low-viscosity aqueous dispersion at high solids at mildly acidic pH, were demonstrated to be effective tablet coating materials. This study focused on the synthesis and evaluation of amphoteric polyacrylate latex-based film forming materials for tablet coatings. A designed series of amphoteric latexes was prepared via emulsion polymerization from acrylic monomers already used in the synthesis of FDA-approved polyacrylate polymers. Polymer composition was systematically varied in order to understand the effects on polymer Tg and film formation temperature, setting efficiency as a function of pH, and film properties such as tack, hardness, extensibility, puncture resistance, optical transmission, gloss, clarity, water permeability, film adhesion to tablets, and tablet coating quality, etc. The resulting latex films showed equal or superior performance compared with commercially-used tablet coatings. The latex-based coatings exhibited high solids (~40 wt. %), good optical properties (clarity > 90%, transmission > 93%, and haze < 6%), no tackiness, and low water vapor permeability (water vapor permeability < 2 x 10-7 g / Pa s m). Dispersions based on the above were prepared with strong acid (SA) / weak base (WB) ionic monomer stabilizers. The two different tablet coatings behave differently at different pHs: the WA/SB-based coating is stable in neutral and higher pHs, but disintegrates readily at pH 2. The SA/WB-based coating is stable at pH 2. We expect that these two types of coatings will enable stomach release (WA/SB-based coating) or enteric release (SA/WB-based coating) of coated drugs. We have demonstrated that latexes with a balance of quick-setting efficiency and tunable coating properties can be prepared. Amphoteric latex-based tablet coatings can be performance- and cost-competitive to HPMC- and PVOH-based coatings, easier to apply from a high solids, low viscosity formulation, and their compositions can be easily adjusted to provide coatings with the desired balance of properties including gloss, adhesion, optical and mechanical properties and glossy, smooth appearance.