Effects of highly hygroscopic
sorbitol,
citric acid,
sodium carboxymethyl cellulose or
polyvinylpolypyrrolidone, on the hydrolysis of
simvastatin in
tablets at 25°/90% RH were studied. The
simvastatin tablets were prepared by direct
powder compression.
Simvastatin and its hydrolyte,
simvastatin acid, were quantitatively analysed by high performance liquid chromotography. The hygroscopicity, water swelling ratio, water solubility and pH of the four hygroscopic
excipients were investigated. During the investigation period, the
weight gain of
sorbitol or
citric acid increased faster than that of
polyvinylpolypyrrolidone or
sodium carboxymethyl cellulose at 25°/90% RH, accordingly, the moisture sorption of the
tablets containing
citric acid or
sorbitol (T-3 or T-6) were more than that of the
tablets containing
sodium carboxymethyl cellulose or
polyvinylpolypyrrolidone (T-4 or T-5). The increase of
simvastatin acid content with time at 25°/90% RH for the
tablets was in the following order: T-6 < T-4 < T-3 < T-5. The effects of the four
excipients on the hydrolysis of
simvastatin in
tablet were related to not only their hygroscopicity but also their other properties, such as moisture retention capacity and pH.
Sorbitol as hygroscopic
excipient in
tablet can most effectively prevent the hydrolysis of
simvastatin in
tablet.