Background: A new preparation of betamethasone valerate in a novel foam vehicle is available for treatment of scalp dermatoses. The vehicle spreads between hair until it reaches the scalp, where it melts and delivers the active drug. Solids make up only a tiny fraction of the foam vehicle, leaving no apparent residue on the skin or hair. The uniqueness of this vehicle raises the question of how to compare it with other topical corticosteroid preparations.
Objective: The purpose of this study was to determine the equivalency of a given quantity of the foam product to quantities of drugs in conventional vehicles.
Methods: The number of fingertip units (FTUs) per gram and the area of coverage of an FTU of betamethasone valerate foam vehicle were determined and compared with those of cream, lotion, gel, and solution psoriasis treatments.
Results: The weight of an FTU of foam vehicle was 52.5 +/- 5.7 microg. There were 9 to 12 times as many FTUs in 100 g of vehicle foam as in 100 g of cream or gel and 2.3 to 2.8 times as many as in 100 g of lotion or solution. The area covered by an FTU of foam vehicle was less than the area covered by an FTU of cream or gel.
Conclusion: The characteristics of foam vehicle are different from those of other vehicles. The greater number of FTUs in 100 g of foam vehicle made up for the lower coverage per FTU, such that total coverage area for 100 g of foam vehicle was comparable to the coverage area for 100 g of the drugs in traditional vehicles.