Solventless Photocurable Film Coating

Generally, tablet and capsule film coatings are applied as aqueous or organic-based polymer solutions or dispersions, graduate student Sagarika Bose (University of Connecticut) explained during her Tuesday AAPS Graduate Student Symposium presentation, "Development and Evaluation of Solventless Photocurable Pharmaceutical Film Coating." However, organic film coatings can be flammable, toxic, and must comply with strict environmental regulations. Aqueous film coating can lead to the degradation of certain drugs by heat and water.

Bose presented a study that suggests using liquid prepolymers for a solventless photocurable film coating that requires no heat and no evaporation step. "The goal is to identify formulation and processing parameters that affect pharmaceutical performance of photocurable coating and further evaluate the coating for immediate- and sustained-release dosage forms," Bose explained.

The coating process begins with 5 g of beads entering a nitrogen-purging stage. Afterward, liquid prepolymer is added, followed by a powdered pore-forming agent. Tablets are sprayed and, finally, the coating is cured under intense light. The process is repeated until a satisfactory layer of coatings is created.

Coating uniformity was determined by image analysis using a 5.1 megapixel sensor camera to determine variations in color, diameter, and roundness. The study varied solid-liquid ratios, numbers of layers, and types of poreformers, including lactose, and PEG800 to gauge release, mechanical strength, and photostability.

"The results show that release can be modified with choice of material, numbers of layers, and length of coating," Bose said. An increase in solid-liquid ratio can theoretically increase the percolation and, in effect, can boost the dissolution of dye. "However, percolation was not significant for lactose in the ranges investigated. Instead, thickness of coating is significant with respect to release."

The PEG8000 was found to release faster than the other pore-formers studied. "We found that there were some defects in coating, which caused faster release," Bose said. And, the four to five layers of coating did not have an effect on release rate, though, six layers dropped the release rate significantly.

Responding to an audience question about long-term storage stability, Bose said that storage stability testing was not performed; however, the light stability tests used high-intensity light for 24 hours and no effect on the coating was evident.