Sodium Starch Glycolate

Purpose:This study explored the potential of combining the use of moisture sorption isotherms and dielectric relaxation profiles of starch and sodium starch glycolate (SSG) to probe the location of moisture in dried and hydrated samples.Methods:Starch and SSG samples, dried and hydrated, were prepared. For hydrated samples, their moisture contents were determined. The samples were probed by dielectric spectroscopy using a frequency band of 0.1 Hz to 1 MHz to investigate their moisture-related relaxation profiles. The moisture sorption and desorption isotherms of starch and SSG were generated using a vapor sorption analyzer, and modeled using the Guggenheim-Anderson-de Boer equation.Results:A clear high frequency relaxation process was detected in both dried and hydrated starches, while for dried starch, an additional slower low frequency process was also detected. The high frequency relaxation processes in hydrated and dried starches were assigned to the coupled starch-hydrated water relaxation. The low frequency relaxation in dried starch was attributed to the local chain motions of the starch backbone. No relaxation process associated with water was detected in both hydrated and dried SSG within the frequency and temperature range used in this study. The moisture sorption isotherms of SSG suggest the presence of high energy free water, which could have masked the relaxation process of the bound water during dielectric measurements.Conclusion:The combined study of moisture sorption isotherms and dielectric spectroscopy was shown to be beneficial and complementary in probing the effects of moisture on the relaxation processes of starch and SSG.

Sodium starch glycolate is a commonly used super-disintegrant employed to promote rapid disintegration and dissolution of IR solid dosage forms. It is manufactured by chemical modification of starch, i.e., carboxymethylation to enhance hydrophilicity and cross-linking to reduce solubility. It has been reported in the literature that the source of starch, particle size, amount of sodium chloride (reaction by-product), viscosity, degree of substitution and cross-linking affect the functionality of sodium starch glycolate. Compendial assays provide an accurate representation of the chemical quality of an excipient, but they are not useful in describing the physical properties associated with the excipients. Physical characterization of sodium starch glycolate, NF revealed differences in particle size, surface area, porosity, surface morphology, and viscosity between two of the three sources examined. An automated liquid uptake test (in neutral and acidic medium) demonstrated similar initial rates of uptake, however, the extent of liquid uptake differed for the disintegrant powders examined. Settling volume was also observed to be different for the disintegrant from two sources. Lowering the pH of the medium reduced the rate and extent of liquid uptake and the settling volume in all instances. The extent of liquid uptake and settling volume was observed to be higher for the smaller sieve fractions in either medium, Although differences were also observed in the axial and radial disintegration force measurements of the pure disintegrant compacts, disintegration and dissolution of a model drug (hydrochlorothiazide) from either the soluble or insoluble core did not reveal any significant differences between the multiple sources.

The internal and surface chemical compositions of three sodium starch glycolate (SSG) products, Explotab, Primojel and Vivastar P were studied using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), time of flight secondary ion mass spectrometry (TOF-SIMS) and 23Na nuclear magnetic resonance spectroscopy (NMR). The surfaces of Explotab and Primojel contained very distinct features containing Na and Cl, however, Primojel also contained features which contained Na which may reflect the presence of Na glycolate and/or Na citrates. Vivastar P contained relatively few surface Cl containing features. Analysis of cross-sections of the particles showed that Na appeared to be uniformly distributed throughout the particles of all the products. Additionally, there was a significant concentration of Cl in the periphery of Explotab and Primojel. In the case of Vivastar P, significant levels of Na and Cl were detected in the internal regions of the particles which, together with 23Na NMR, suggests that NaCl is uniformly distributed within Vivastar P. 23Na NMR also suggested that the ratio of organic Na to NaCl was considerably lower in Vivastar P than Primojel and Explotab. Overall, even though all these three products satisfy the pharmacopeial descriptions of SSG, these studies suggest that Primojel and Explotab exhibit different chemical compositions to Vivastar P. Since the three products studied are reported to be prepared from potato starch, the apparent differences in chemical composition probably reflect the different manufacturing processes used, however, batch to batch variations may account for some of the subtle differences.