The time course of dexamethasone delivery using iontophoresis through human skin, measured via microdialysis.

STUDY DESIGN Controlled laboratory study. OBJECTIVE To determine the time course of dexamethasone sodium phosphate (Dex-P) during iontophoresis to underlying tissues using microdialysis. BACKGROUND In human participants, real-time information of Dex-P transdermal delivery during iontophoresis is unknown. METHODS Sixty-four healthy male participants (mean ± SD age, 24.2 ± 3.3 years; height, 181.8 ± 26.1 cm; mass, 82.4 ± 11.8 kg; subcutaneous fat thickness, 0.61 ± 0.19 cm) were randomly assigned into 1 of 6 groups: (1) 1-mA current, 1-mm probe depth; (2) 1-mA current, 4-mm probe depth; (3) 2-mA current, 1-mm probe depth; (4) 2-mA current, 4-mm probe depth; (5) in vivo retrodialysis; and (6) skin perfusion flowmetry. Microdialysis probes were used to assess the combined recovery (Dex-total) of Dex-P, dexamethasone, and its metabolite. RESULTS There was no difference in Dex-total between current intensities (P = .99), but a greater amount of Dex-total was recovered superficially at 1 mm compared to the 4-mm depth (P<.0001). Peak concentration mean ± SD values for the 1- and 2-mA currents at 1 mm were 10.8 ± 8.1 and 7.7 ± 5.5 µg/mL, and at 4 mm were 2.0 ± 0.8 and 1.3 ± 0.9 µg/mL, respectively. Peak skin perfusion was 741.4% ± 408.7% and 711.6% ± 260.8% at baseline for 1- and 2-mA intensities, respectively. Skin perfusion returned to baseline levels earlier during 1-mA intensity at a 110 mA · min dose within the treatment, compared to 2 mA at 60 minutes posttreatment. CONCLUSION Transdermal delivery of Dex-P during iontophoresis was successfully measured in vivo through human skin. Measurable concentrations of Dex-total were found regardless of current intensity. Although current-induced vasodilation occurred, it did not significantly affect the tissue accumulation of Dex-total.