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Abstract
Uncoated Sabril® tablet cores under long term storage become slightly discolored from the initial white to a yellowish off-white color. In order to ensure the aesthetics of the product, Sabril tablet cores are film coated with an opaque white coating. The nature of this yellowing reaction was of interest even though discolored tablets showed no significant loss of potency on assay. Excipient compatibility studies showed that the vigabatrin active in Sabril mixed with Avicel (microcrystalline cellulose) in the presence of moisture also became off-colored when stressed at elevated temperatures.
The nature of the discoloration in aged Sabril core tablets was investigated. Chromatographic and spectroscopic data indicate that the source of this color comes from the Maillard Reaction between vigabatrin and Avicel which results in a multitude of products analogous to “browning reactions” of food products. A gravimetric determination of the leached colored products from 7 year old Sabril core tablets gave a residue of less than 0.1% relative to vigabatrin. Furthermore, based on spectroscopy, most of this residue was found to be povidone, an excipient in the tablets which was isolated along with the colored substances.
Therefore, the colored products identified in the core of Sabril tablets stored for an extended period of time represent only minor impurities. Their formation through aging arises via the Maillard Reaction and would only constitute a matter of aesthetics. The latter problem is avoided by the currently employed film coating process.
Similar reactions could be predicted for other drugs having amine functional groups if they are formulated with microcrystalline cellulose or reducing sugars.