A model to assess the effectiveness of topical antipruritics.
A model has been developed to determine the effectiveness of topical antipruritics. It utilizes controlled, experimentally induced itch and has demonstrated the effectiveness of the direct action on cutaneous receptor sites of a topical anesthetic, benzocaine, in a topical antipruritic formulation, and has been used to differentiate between two effective topical antipruritics. Three studies are presented: The first study examined the reliability of the experimentally induced itch. Several indices of reliability were computed from the data of this first study. Cronbach's alpha was 0.92. Winer's theta also was 0.92. Simple test-retest reliability, computed at intervals of 29 min, 1 day, and 6-7 days, resulted in Pearson correlations of 0.84, 0.73, and 0.60, respectively. In the second study, the model differentiated statistically between the itch relief resulting from the topical application of a formulation with 6% benzocaine and the same formulation without benzocaine. The third study examined 2 known topical antipruritics: one containing 6% benzocaine and the other 1% hydrocortisone. Both topical antipruritics were found to relieve itch; however, the benzocaine antipruritic produced statistically significantly greater itch relief in more subjects than the hydrocortisone antipruritic at both 1 and 30 min after application. These results demonstrate that OTC antipruritics can be differentiated for effectiveness.