Formulation factors affecting release of drug from topical formulations. 1. Effect of emulsion type upon in vitro delivery of ethyl p-aminobenzoate.
There are numerous kinetic and thermodynamic processes which occur during the transport of a topically applied drug from within its vehicle to the site of action in the skin. The present study compares the release and permeation of a model compound, ethyl p-aminobenzoate, from water, mineral oil, a mineral oil in water (O/W) emulsion, and a water in mineral oil (W/O) emulsion. These formulations are compared for differences in transport characteristics using in vitro diffusion studies and a synthetic polydimethylsiloxane membrane. Two factors appear prominent in influencing the release kinetics of the drug from its formulation. The first is the observation that the drug is released 2 times slower from mineral oil than from water at approximately equivalent thermodynamic activities, and the second is the appreciable lowering of the thermodynamic activity as a result of substantial micellar solubilization of the drug in the aqueous phase of the O/W emulsion. The thermodynamic activity effect predominants, resulting in a lower release rate from the O/W emulsion as compared to the W/O emulsion.
Lalor
C B
CB
College of Pharmacy, University of Michigan, Ann Arbor 48109-1065.
Flynn
G L
GL
Weiner
N
N
D000287:Administration, Topical; D001566:Benzocaine / Q000008:administration & dosage* / Q000737:chemistry; D002853:Chromatography, Liquid; D004058:Diffusion; D004129:Dimethylpolysiloxanes; D004339:Drug Compounding; D004655:Emulsions; D008567:Membranes, Artificial; D008899:Mineral Oil; D012995:Solubility; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics; D014867:Water
D004129:Dimethylpolysiloxanes; D004655:Emulsions; D008567:Membranes, Artificial; D014867:Water; D008899:Mineral Oil; D001566:Benzocaine