Solubilization capabilities of some cationic, anionic, and nonionic surfactants toward the poorly water-soluble antibiotic drug erythromycin

Surfactants can be used to increase the solubility of poorly soluble drugs in water and to increase drug bioavailability. In this article, solubilization of macrolide antibiotic erythromycin is investigated by employing spectrophotometry and tensiometry in micellar solutions of nonionic (Brij56, Brij58, Brij35, Brij30), cationic (cetyltrimethylamonium bromide, CTAB; tetradecyltrimethylammonium bromide, TTAB; dodecyltrimethylammonium bromide, DTAB), and anionic (sodium dodecylbenzenesulfonate, SDBS; sodium dodecylsulfate, SDS) surfactants and then compared. The results showed that irrespective of the surfactant type, the solubility of erythromycin increases linearly with increasing surfactant concentration, as a consequence of association between the drug and micelles. Solubilization capacity has been quantified in terms of molar solubilization ratio (R-m,R-S), micelle-water partition coefficient (K-M), binding constant (K-1) between solubilizate monomer and vacant micelle, and the free energy of solubilization (Delta G(s)degrees) of the drug in the micelles. Cationic surfactants of the same chain length as that of nonionic and anionic surfactants exhibited higher solubilization capacity, probably due to solubilization at the micelle-water interfaces. The order of solubilization powers among nonionic, cationic, and anionic surfactants for erythromycin was found to be Brij56 > Brij58 > Brij35 > Brij30, CTAB > TTAB > DTAB, and SDBS > SDS, respectively. This comparative study can be used to select an appropriate medium for erythromycin solubilization, where nonionic surfactants are advantageous due to their minimal protein binding and retention of their micellar form even after large dilution in blood owing to their very low critical micellar concentration (cmc) values.