The present study was undertaken to examine the effect of pH and concentration of hydroxypropyl-beta-cyclodextrin on the solubility of carvedilol as it shows pH-dependent solubility. The equilibrium solubility of carvedilol in a series of solutions of varying pH (from 1.2 to 11) was determined and compared with the equilibrium solubility of carvedilol in the presence of 20% hydroxypropyl-beta-cyclodextrin at same pH values. It was observed that solubility of protonated form is more than neutral molecule. Hydroxypropyl-beta-cyclodextrin resulted in increased solubility at all the pH. But inclusion in the cavity of hydroxypropyl-beta-cyclodextrin might depend upon charge state of the molecule. So it can be concluded that solubility of carvedilol, can be increased either by the addition of hydroxypropyl-beta-cyclodextrin or by adding pH lowering agents. But both these methods if are to be used together, pH should be selected carefully.
Keywords: Carvedilol; bioavailability; hydroxypropyl-β-cyclodextrin; pH; solubility.