The effect of composition and ageing on the dissolution rates of chlorpropamide-urea solid dispersions

Discs of chlorpropamide and urea have been prepared by (a) melting and (b) compression. Intrinsic and relative dissolution rates of the discs have been measured and the dissolution process investigated microscopically. Higher dissolution rates were found from melts than from physical mixes. The optimum dissolution rate composition found was for a melt composed of 30% w/w chlorpropamide which possessed an intrinsic dissolution rate 930 times greater than for the pure drug. Sphere formation, during dissolution rate measurement has been observed and a likely mechanism proposed to account for its occurrence. Dissolution rates generally increased with age for most melt compositions.