An investigation into moisture barrier film coating efficacy and its relevance to drug stability in solid dosage forms.

Barrier coatings are frequently employed on solid oral dosage forms under the assumption that they prevent moisture sorption into tablet cores thereby averting premature degradation of moisture-sensitive active ingredients. However, the efficacy of moisture barrier coatings remains unproven and they may actually accelerate degradation. This study aimed to investigate the barrier performance of four coating systems following application onto a low hygroscopic tablet formulation containing aspirin as a model moisture sensitive drug. Tablets were prepared by direct compaction and coated with aqueous dispersions of Eudragit(®) L30 D-55, Eudragit(®) EPO, Opadry(®) AMB and Sepifilm(®) LP at the vendors' recommended weight gains. Moisture uptake was studied by dynamic vapor sorption at 0 and 75% RH (25°C). Accelerated stability studies were undertaken at 75% RH/25°C for 90 days and HPLC assay was used to determine aspirin content. Uncoated tablet cores equilibrated rapidly and took up very little water (0.09%). The mean water uptake for coated cores was higher than for the uncoated formulation and varied as follows: 0.19% (Eudragit(®) L30 D-55), 0.35% (Opadry(®) AMB), 0.49% (Sepifilm(®) LP) and 0.76% (Eudragit(®) EPO). The level of aspirin decreased in all the samples such that by the time the study was terminated, the mean aspirin recovered was as follows: uncoated cores 80.0%; Eudragit® L30 D-55 coated cores 78.8%; Opadry(®) AMB coated cores 76.2%, Sepifilm(®) LP coated cores 76.0% and Eudragit(®) EPO coated samples 66.5%. From these results, it is concluded that the efficacy of moisture barrier polymer coatings on low hygroscopic cores is limited, and application of these coatings can, instead, enhance drug degradation in solid dosage forms.