Chemical, pharmaceutical and clinical standardization of the TRUE Test caine mix.

The development of the caine mix patch of the TRUE TestTM involved extensive formulation work to obtain optimal release, stability and clinical function. Hydroxypropyl cellulose, ordinarily used in the TRUE TestTM, induced crystallization and inadequate release of benzocaine. Addition of the crystal poison glucose caused rapid degradation of the caines. Polyvinylpyrrolidone (PVP) proved to be a vehicle which incorporated the caines in a stable preparation on the patch. Rapid release of the caines from this vehicle when applied on membranes was confirmed by in vivo patch test studies.