Kj. Miller et al., EVALUATION OF LOCAL-ANESTHESIA PROVIDED BY TRANSDERMAL PATCHES CONTAINING DIFFERENT FORMULATIONS OF TETRACAINE, Journal of pharmaceutical sciences, 82(11), 1993, pp. 1123-1125
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].