EVALUATION OF LOCAL-ANESTHESIA PROVIDED BY TRANSDERMAL PATCHES CONTAINING DIFFERENT FORMULATIONS OF TETRACAINE

Topical formulations of tetracaine in vehicles of propylene glycol and saline are tested on human volunteers with standard occlusive, adhesi ve, transdermal patches. The effects of formulation composition, dose, and onset time are investigated. Dose-response studies indicate that the optimum formulation for the diffusion of tetracaine in vivo is 60% free base and 40% acid salt (w/w) in 40% propyLene glycol and 60% sal ine (v/v). A concentration of 0.3 M [8.3% (w/v)] tetracaine is suffici ent to reach the dose plateau. Time-response studies indicate that hig h concentrations of tetracaine in the optimum formulation [1.1 and 1.8 M, 30 and 50% (w/v), respectively] can produce statistically signific ant analgesia relative to a placebo after 45 min. Comparison of these in vivo data with earlier in vitro data indicate that the optimum form ulation with regard to clinical studies is identical to that for in vi tro diffusion through hairless mouse skin [60% free base and 40% acid salt (w/w) in 40% propylene glycol and 60% saline].