Colonic spread of 5-ASA enemas in healthy individuals, with a comparison of their physical and chemical characteristics.

BACKGROUND

5-aminosalicylic acid (5-ASA) is widely used as topical treatment in patients with distal inflammatory bowel disease. The enema spread and retention time are considered to be important factors in the efficacy of this therapeutic agent. Whereas colonic spread is widely investigated in selected patient populations and volunteers, much less attention has been given to the in vitro differences of physical and chemical properties, although they may influence the in vivo characteristics.

METHODS

Two different brand enemas, Salofalk and Asacol, both containing 2 g mesalazine, were compared with respect to their in vivo and in vitro characteristics. The retrograde spread, maximum distribution and wall adhesion, as well as the retention time of the enemas, was examined by the addition of a technetium tracer dose in 12 healthy volunteers on two separate occasions. In addition, several chemical properties such as pH, viscosity, particle size, dispersion rate, specific surface area and residual volume after application were analysed and compared.

RESULTS

With its larger volume and higher viscosity the Asacol preparation reached a substantially larger proportion of the colon and produced a significantly higher retention time in the proximal parts of the large intestine. In addition, more than double the amount of 5-aminosalicylic acid was not expelled from the semi-rigid Salofalk enema container after application. With respect to chemical properties it was demonstrated that the Asacol preparation showed a significantly smaller size of micronized 5-aminosalicylic acid particles, better homogeneity and much less aggregation of the drug. This resulted in an almost threefold higher specific surface area per g active compound.

CONCLUSIONS

The Asacol enema appears to be superior in several aspects of the galenical formulation. The better dispersion and larger specific surface area, in conjunction with a larger distribution, better bowel wall adherence and retention time in vivo, constitute a clear theoretical and possible clinical advantage.