The etiology of pinhole and bubble defects in enteric and controlled-release film coatings

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Abstract
Film coatings are frequently applied to tablets or pellets in order to control or delay the release of medication from these dosage forms. Pinhole and bubble defects create weak points in the film through which fluid can penetrate relatively easily. It is postulated that bubble defects are continuously formed on the surfaces of tablets and pellets during the film coating operation because of foam produced by spray atomization of the coating solution. These bubbles are broken down rapidly during particle-to-particle collisions as the coating operation proceeds. Logos and very rough surfaces form protected areas free from abrasion which allow the bubbles to set or partially collapse to form pinholes.