Background: Preparation of mini buccal tablets incorporating either of the Alzheimerâ��s drugs, rivastigmine tartrate\nor donepezil hydrochloride, were developed for patients who have difficulty swallowing as a source of effervescence,\nby pairing the less commonly used malic acid with sodium bicarbonate in an experimentally determined (1:2)\nstochiometirc ratio.\nMethods: To avoid premature reaction of the acid and the base during compounding, the tablet ingredients\nwere mixed in the following order: acid, sweetener, binder, drug, preservative, base, and anti-adherent/lubricant.\nResults: An accelerated thermal stability study at 40 �°C and 25% relative humidity showed that the integrity of the\neffervescent tablets containing rivastigmine tartrate were superior to that of donepezil HCl tablets. FT-IR spectrometry\nconfirmed the presence of water of hydrate in donepezil HCl crystals. This water was absent in the IR after one-month\nstorage at accelerated thermal stability, but was present at room temperature. This behavior was not observed in the\ntablet made from rivastigmine tartrate powder. Differential scanning calorimetry of donepezil hydrochloride showed\ntwo thermal events: the first was associated with the loss of the water, and the second, at much higher temperature,\nwas the melting of theanhydrous drug. Such behavior was not observed in the rivastigmine tartrate powder.\nConclusions: Hidden water which may function as catalyst to induce premature effervescence during storage.
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