The Effects of Formulation Variables on Iontophoretic Transdermal Delivery of Leuprolide to Humans

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Abstract
Feasibility of applying iontophoresis to facilitate the transdermal permeation of leuprolide acetate was investigated. Because of the complexity of the factors involved in the process of iontophoresis, theoretical predictions of the combination effects from formulation variables are difficult. This study incorporated the formulation variables, drug levels and buffer concentrations, in a device prepared by Drug Delivery System, Inc., to assess the feasibility for leuprolide delivery. Steady state serum leuprolide concentrations were achieved within 30 minutes of patch application, and were maintained for the duration of the study period. An increase in LH levels was observed for each formulation. The serum leuprolide concentrations were higher with lower drug concentration and more dilute buffer solutions. Increasing drug concentration in the patch appeared to inhibit delivery of leuprolide. A mean steady state serum concentration, 0.8 ng/ml, was achieved by a formulation composed of 10 mg/ml leuprolide acetate and 0.05 M acetate buffer at pH 5.0. Competitive reaction of ions possibly involved in the delivery mechanism will be discussed.