EVALUATING THE IRRITATION POTENTIAL OF SKIN PENETRATION ENHANCERS IN THE HAIRLESS GUINEA-PIG

Nine skin penetration enhancers were evaluated for skin irritation eff ects. The evaluation was done by a modified Draize test using the hair less guinea pig as a model. This model has the advantage that no hair clipping was necessary, compared with the normal guinea pig, rat, or r abbit model, and hence eliminated a possible source of error. Each ani mal was scored by seven observers for erythema/eschar formation and ed ema at 4, 24, 48, and 72 h after application of the test solution. The scoring used was defined by the Code of Federal Regulations. The scor es were interpreted for irritation as defined by the National Institut e of Occupational Safety and Health. The compounds tested were solutio ns of N-N-diethyl-m-toluamide, 1-dodecylazacycloheptan-2-one (atone), n-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethyl formamide, dimeth yl acetamide, lauric acid, oleic acid, and cetyl trimethyl ammonium br omide. A dilute solution of thioglycolic acid was used as a positive c ontrol. The results indicate that dimethylsulfoxide and azone were mil dly irritant only during the initial 24 h. The other chemicals were no nirritant. Where available, the effects were compared to the literatur e on the human skin. The hairless guinea pig model was useful in defin itely eliminating irritant compounds and appears to be a reasonable in dicator of mild irritants. The model is useful in the initial screenin g of potential skin penetration enhancers.