Oral Sustained Release of a Hydrophilic Drug Using the Lauryl Sulfate Salt/Complex

The objective of this study was to establish the key factor of the lauryl sulfate (LS) salt/complex for sustained release of a hydrophilic drug at various physiological pH levels. Mirabegron is a hydrophilic drug that exhibits pH-dependent solubility. Sodium lauryl sulfate (SLS) bound to mirabegron in a stoichiometric manner. The formation of the LS salt/complex significantly reduced mirabegron solubility and helped achieve sustained release of mirabegron over a wide range of pH levels. In addition to SLS, other additives containing a sulfate group formed salts/complexes with mirabegron and reduced its solubility at different pH levels. Furthermore, octyl sulfate (OS), myristyl sulfate (MS), and cetyl sulfate (CS) salts/complexes, which contain alkyl chains of different lengths, showed a lower solubility than mirabegron and promoted sustained release of mirabegron. The rank order of solubility and dissolution rate were as follows: OS salt/complex>LS salt/complex>MS salt/complex>CS salt/complex, which corresponded to the rank of alkyl chain lengths. We conclude that the presence of a sulfate group and the length of the alkyl chain are key factors of the LS salt/complex for sustained release of a hydrophilic drug at various physiological pH levels.