Development and evaluation of solventless photocurable pharmaceutical film coating

Solventless coating technologies can overcome many of the limitations associated with the use of solvents in pharmaceutical coating. Two solventless photocurable film coating system were investigated where non-pareil beads were coated with a solventless photocurable film coating in a mini-coating pan using photocurable (1) prepolymers and cured by UV light, and (2) monomers and cured by visible light. Each layer of coating consisted of liquid prepolymer/monomer and powdered solid pore-forming agents. Using lactose as a pore-forming agent, optimum ratio of the amount of pore-forming agent in mg (S) to volume of photocurable prepolymer/monomer in μl (L) to achieve good process efficiency and uniformity was 1.8-3.0. The S/L ratio was sensitive to particle size and type of pore-forming agent as well as the viscosity of the monomer mixture in the case of the visible light curable coating system. Initiator (and photo-sensitizer in visible light curing system) concentration, exposure time, light intensity and total exposure of light were also evaluated and were shown to influence the percent conversion of prepolymer/monomer to polymer. Immediate release of a blue dye contained in the non-pareils was obtained for both UV and visible light curing system with sodium starch glycolate as a pore-former, since it swelled producing large pores. Simple pore-formers (lactose and sodium chloride) simply dissolved away and provided a more sustained release profile. Release from the coating was modifiable with the choice of pore-forming agent, number of layers, coating thickness as well as mixing two groups of non-pareils coated with different pore-forming agents. The nature of the scaffold and pore structure of the coating were determined by simultaneously monitoring the release of sodium chloride from the coating and the blue dye from the beads. At least 40-50% of the sodium chloride that was incorporated in the coating released before the dye released through the coating showing that pore-formation was a necessary process prior to the release of the marker dye. The coupling between dye release and pore-formation was found to be dependent on the S/L ratio of the coating. Simulation based on percolation theory showed that the coupling of pore-formation and dye release was higher when the variance in tortuosity was lower. Additional studies demonstrated that the coating was photostable and could withstand handling stress.