Effects of sodium taurodihydrofusidate on nasal absorption of insulin in sheep.
To investigate the utility of a novel adjuvant, sodium taurodihydrofusidate (STDHF), as an enhancer of mucosal permeation of drugs, experiments involving intranasal insulin:STDHF administration in sheep were performed. Rabbit erythrocyte lysis assays were employed to assess the relative membrane lytic activity of STDHF, as well as that of its glycine-conjugated analogue, compared with a nonionic detergent and a common bile salt. Equivalent weight concentrations of the fusidates were found to be 5- to 10-fold less lytic than the bile salt and at least 100-fold less lytic than the nonionic detergent laureth-9. Provided the concentration of STDHF was greater than its critical micellar concentration, formulations of insulin with STDHF greatly enhanced intranasal insulin absorption. Optimal nasal insulin absorption was attained at a molar ratio of STDHF to insulin of 5:1. In addition, intranasal absorption was linearly related to insulin dose. Compared with intravenous administration, the mean bioavailability of intranasal insulin was 16.4%. Interovine variability was low, with a coefficient of variation of 14% for 12 animals. It was found that intranasal absorption of sodium insulin was not significantly different from that of zinc insulin. However, formulations of both crystalline insulin preparations were absorbed more efficiently than a formulation prepared using commercially available solutions of U-500 insulin. The results taken together indicate that STDHF is an excellent enhancer of insulin absorption from the nasal mucosa.