Interaction of benzocaine with polymeric materials

Benzocaine is a widely used local anaesthetic. It has been demonstrated that the loss of active ingredient from tablets is due to an absorption of benzocaine by the polymer stopper. In this paper, we present a simple method allowing studies of the interaction of benzocaine or other compounds characterized by relatively high sublimation pressure with polymeric materials. In the case of the polyolefins HDPE, LDPE and PP, the extent of benzocaine absorption can be explained on the basis of the free-volume concept of diffusion. The interaction of benzocaine with PVC is however rather complex. Obviously the compound acts as a plasticizer. As a consequence of an initial benzocaine uptake, the glass transition temperature decreases. This results in an increase in additional benzocaine uptake.