Effects of microemulsions components on in vitro permeation and in vivo activity of benzocaine

Abstract

To investigate microemulsion formation, capric/caprylic triglyceride was used as oil component. Sorbitan stearate (and) methylglucose sesquistearate, polyoxyethylene sorbitan monooleate and polyoxyethylene (10) eleyl ether were used as surfactants, n-butanol and glycerin were used as co-surfactants. The area of microemulsion was increased by using the n-butanol as co-surfactant while the area of microemulsion was lowered by using glycerin as co-surfactant. Using polyxyethylene (10) oleyl ether:n-butanol in the ratio of 1:1 by weight produced the largest region of microemulsion in phase diagram. To investigate the effect of microemulsions components on in vitro permeation and in vivo activity, 7.5% by weight benzocaine as a model drug were incorporated in microemulsion consisted of capric/caprylic triglyceride, water and polyoxyethylene (10) oleyl ether. The in vitro permeation studies were determined by Franz cell using shed cobra skin as membrane, and in vivo activities were measured using mouse tail flick test. The results indicated that benzocaine permeation was increased as water content in the microemulsion increased, but was decreased as surfactant concentration in the microemulsion increased. The in vitro permeation results were significantly correlated with in vivo local anesthetic activity (p<0.01).