Bioavailability and Diuretic Effect of Bumetanide Following Rectal Administration of Suppositories Containing Weak Acids in Human Subjects

The bioavailability of bumetanide following the oral administration of tablets, or the rectal administration of either macrogol suppositories or suppositories with and without weak acids were evaluated in human subjects. The absorption of bumetanide from those suppositories containing bumetanide without weak acids (control suppositories) was extremely poor, while the absorption from those suppositories containing citric acid or tartaric acid was enhanced. The mean area under the plasma concentration-time curve (AUC) following the rectal administration of the suppositories containing citric acid and tartaric acid was 52 and 62%, respectively, of that following the oral administration. On the other hand, the absorption rate constant (ka) and the mean residence time (MRT) following the rectal administration of the suppositories containing weak acids increased significantly compared to those administered orally. The time (Tmax) required to achieve the maximum plasma concentration (Cmax) in the plasma following the rectal administration of the suppositories containing weak acids was significantly shortened compared to the time of those administered orally. These results indicated that the bumetanide contained in the suppositories containing weak acids might be absorbed rapidly after administration. The diuretic effect of bumetanide following the oral and rectal administration was also evaluated. Sufficient diuretic effects were obtained following the rectal administration of the suppositories containing weak acids.