Quantification of total dexamethasone phosphate delivery by iontophoresis

The total amount of dexamethasone phosphate transferred into the human body as a function of iontophoresis has not previously been determined, despite its widespread clinical use in the treatment of localized inflammation. The objective of this study was to document the optimal parameters required for clinical iontophoresis of dexamethasone phophate. Results were achieved by the experiment of in vitro evalutations of dexamethasone phosphate iontophoresis and by in vivo estimations of drug amounts (milligrams) iontophoresed into healthy human volunteers. The in vitro evaluations were conducted to quantify total dexamethasone phosphate amounts transferred as a function of dosage (milliAmp-minutes), to evaluate the efficiency of the delivery based on dexamethasone phosphate only (pure) donor solutions compared with dexamethasone phosphate + salts (coformulated) donor solutions, and to compare the delivery from the negative electrode (cathode) with that from the positive electrode (amode). The in vivo drug amounts were estimated by the use of the formulation conditions determined from the in vivo testing. The in vitro evaluations were conducted with side-by-side glass diffusion cells, which measured iontophoretic and passive delivery across an ultrafiltration membrane. The in vivo experiments were conducted on five healthy human volunteers who were wearing a low-voltage iontophoreses system. Total drug delivery was ascertained by the difference between the initial drug load and a final residual amount determined by extraction. The in vitro results demonstrated increased dexamethasone phosphate delivery with higher iontophoretic dosages and with the pure dexamethasone phosphate formulation. Delivery from the anode was significantly lower than that from the cathode. After an 80-mA-minute drug-delivery was administered, the in vivo iontophoretic delivery was measured to be 1.40 +/- 0.23 mg, and the corresponding passive delivery was 0.26 +/-0.16 mg. The in vitro experiments confirm iontophoretic delivery of dexamethasone phosphate across artificial membranes, and the in vivo experiments suggest that drug is delivered into human skin.