Modification of diffusion rates of benzocaine from topical vehicles using sodium salicylate as complexing agent

The release of benzocaine from various topical vehicles containing benzocaine, alone and in the presence of a complexing agent, sodium salicylate, was measured at 37 degrees using dialysis through a cellulose membrane. Sodium salicylate had a marked effect on the release of benzocaine, depending upon the the type of vehicle, with the largest increase observed for the water-miscible base, polyethylene glycol (macrogol ointment BPC). The amount of drug released from preparations containing 1% (w/w) and 2% (w/w) benzocaine in this vehicle depended upon the sodium salicylate concentration. Results are discussed in terms of the differing physical properties of the complexes formed.