Ion-Pairing of Dyclonine with Dyes

This potential for ion-pairing between dyclonine, a local anesthetic, and pharmaceutical dyes commonly used in liquid pharmaceutical formulations was examined. Occurrence of ion-pairing at a pH of 3 was confirmed by shift of the absorption maximum of all five sulfonate-containing dyes, and by measurements of octanol/water partition coefficient and surface tension. There was also an increase in the uptake of dyclonine by phosphatidylcholine liposomes in the presence of a dye (tartrazine) at pH 3 but not at pH 7, where the uncharged anesthetic is dominant.