Pharmacokinetics of bisphenol A in humans following dermal administration

Background: Human exposures to bisphenol A (BPA) are widespread. The current study addresses uncertainties regarding human pharmacokinetics of BPA following dermal exposure. Objective: To examine the absorption, distribution, metabolism and excretion of BPA in humans following dermal administration. Methods: We dermally administered deuterated BPA (d6-BPA) to 10 subjects (6 men and 4 women) at a dose of 100 mu g/kg over a 12-hour period and conducted blood and urine analysis from the beginning of dosing through a three- or six-day period. We present time-course serum and urine concentrations of total and unconjugated (free) d6-BPA and used this information to calculate terminal half-life and area under the curve. Results and Conclusions: Detectable serum levels of total d6-BPA were observed at 1.4 h after the start of dosing, and a maximum serum concentration (C-max) of 3.26 nM was observed. Free d6-BPA was detectable in serum 2.8 h after start of dermal administration, with C-max of 0.272 nM. Beginning at approximately seven hours and continuing to 12 h (which corresponds to cessation of exposure), the concentration of free and total serum d6BPA plateaued. The terminal half-lives of total d6-BPA and free d6-BPA in the body were 21.4 +/- 9.81 h and 17.6 +/- 7.69 h, respectively. Elimination from the body was rate-limited by kinetics in the dermal compartment. Free d6-BPA was a greater percentage of the area under the curve of total serum BPA (8.81%) compared to the 0.56% observed in our previously published oral study. Recovery of total d6-BPA in urine was < 2% of the applied dose after six days. Analysis of the area under the curve for dermal and oral administration revealed that 2.2% of the dermal dose became systemically available. These data are in line with prior studies indicating how pharmacokinetics of BPA differ following oral and dermal exposures. Dermal exposure resulted in a longer apparent half-life and higher free:total d6-BPA ratio compared to oral.