A fluorescence parameter based analysis on the solubilization of carvedilol by bile salt media

Carvedilol (CVL), a β-adrenergic receptor, is insoluble under physiological conditions and hence its oral administration is difficult. Bile salts are widely used as drug delivery media for many hydrophobic drugs. CVL has a strong intrinsic fluorescence with a carbazole moiety. When excited at 320 nm, it exhibits dual emission at 347 and 357 nm. As the concentration of bile salt is increased there is an overall increase in the fluorescence intensity and also the ratio of the intensities at 347 and 357 nm (I(1)/I(2)) increases. This indicates that the CVL molecule can sense the non-polar nature of bile salts with increasing concentrations. It is showed that the new parameter (I(1)/I(2)) can be used as an indicative tool in determining the polarity of the medium. The increase in fluorescence anisotropy and fluorescence lifetimes is observed, indicating the micro-heterogeneity of the bile salt solutions as experienced by CVL molecules. The possibility of electrostatic interactions between CVL and bile salt micelles is ruled out in view of the results obtained here and their interaction is purely hydrophobic in nature. The results suggest that the CVL molecule associates with the steroidal moiety of bile salts through its carbazole moiety.