2002 Volume 28 Issue 6 Pages 521-529
Guanidine hydrochloride, which is known to be effective in the treatment of Lambert-Eaton myasthenic syndrome, is very hygroscopic. Therefore, the mixture of the drug and lactose dispensed at hospital pharmacies tends to easily liquefy even under ordinary storage conditions because of poor compatibility. In this study the physicochemical and chemical stabilities of commercially available guanidine salts, namely hydrochloride, nitrate, carbonate, and sulfate, were investigated at various relative humidity levels. The critical relative humidity of the hydrochloride salt was significantly lower than the others and it was also more hygroscopic than the other three salts, however, nitrate was found to be sufficiently stable regarding humidity. The powder maintained a good flowability after long storage periods. The optimal diluent was selected to use in powders consisting of guanidine hydrochloride in order to stabilize the physicochemical and chemical properties. No solidification or change in appearance were observed in the mixture of the drug and magnesium aluminometasilicate (Neusilin® US2) as diluent and moisture adsorbent. The flow property (angle of repose) of this mixture was also investigated.
