In vitro and In vivo percutaneous absorption of 14C-octamethylcyclotetrasiloxane (14C-D4) and 14C-decamethylcyclopentasiloxane (14C-D5)

Octamethylcyclotetrasiloxane (D-4) and decamethylcyclopentasiloxane (D-5) are cyclic siloxanes used as chemical intermediates with some applications in consumer products. The in vitro percutaneous absorption of C-14-D-4 and C-14-D-5 was studied in flow-through diffusion cells. Single doses were applied neat and in antiperspirant formulations to dermatomed human skin for 24 h. The majority of applied D-4 and D-5 (similar to 90%) volatilized before being absorbed. Only 0.5% of applied D-4 was absorbed while the absorption of D-5 (0.04%) was one order of magnitude lower. The largest percentage (> 90%) of the absorbed D-4 and D-5 was found in the skin. The fate of D-4 and D-5 absorbed in the skin was studied in rat in vivo. A single dose of C-14-D-4 (10, 4.8 and 2 mg/cm(2)) and C-14-D-5 (10 mg/cm(2)) was topically applied inside a dosing chamber attached to the dorsal area. Rats were housed in metabolism cages up to 24 h to enable collection of urine, feces, expired/escaped volatiles. The majority of applied D-4 or D-5 had volatilized from the skin surface. Less than 1.0% of the applied D-4 and only 0.2% of applied D-5 was absorbed with approximately 60% of absorbed D-4 and 30% of absorbed D-5 reaching systemic compartments. The amount absorbed into the skin decreased with time showing that residual D-4 and D-5 diffused back to the skin surface and continued to evaporate. Overall, a low tendency to pass through the skin into systemic compartments was demonstrated for both D4 (<= 0.5% of applied dose) and D-5 (< 0.1% of applied dose). (c) 2007 Elsevier Inc. All rights reserved.