Half an hour versus three hour contact of topical steroid (clobetasol propionate)

Steroids when left on the skin for longer duration may contribute to the side effects without any additional clinical benefit. The relationship between the duration of topical steroid contact with the skin and its effectiveness has not been established. The ability of the topical steroids to inhibit the size of histamine induced wheal was used to assess their relative efficacy.

To determine whether half an hour contact and three hour contact of a topical steroid, clobetasol propionate, is equally effective in inhibiting the size of the histamine induced wheal.

On 30 volunteers, 4 squares were marked on flexor aspect of both forearms using a template. One fingertip unit of clobetasol propionate 0.05% was applied on all the areas. Half an hour later all areas of left forearm and last square of right forearm were wiped. Prick testing was done with histamine and size of wheal recorded after 15 minutes. Similarly steroid was wiped from the 1st, 2nd, 3rd square after 1 hr, 2 hr and 3 hrs on right forearm and the corresponding areas prick tested on both forearms.

There was statistically significant wheal suppression at the end of 2 hrs and 3 hrs as compared to half an hour.

We conclude that half an hour application of clobetasol propionate is ineffective and that it is effective only after two hours of contact and hence short contact of half an hour will be less effective than relatively prolonged contact of 2 hours.