Microneedles array is a new transdermal drug delivery technique designed to create holes in the epidermis and penetrate the stratum corneum, thus avoiding the high resistance of this barrier. Microneedles have been shown to increase the skin permeability of drugs with no or little pain. However, the skin permeability of epidermis while using microneedle arrays has yet to be fully studied. In some cases, microneedle and microneedle array designs which were developed based on certain criteria (e.g., material of the microneedles) have to be related to other criteria (e.g., drug permeability in skin, skin thickness, etc.). Therefore, in order to determine the optimum design of the microneedle arrays, the effect of different factors (e.g., number of the microneedle, surface area of the patch, etc.) along with skin permeability by using microneedles should be determined accurately. In this work, an optimization framework for transdermal delivery of high molecular weight drug from microneedle is presented. The outputs of this framework have allowed us to identify the optimum design of various microneedles. Data from this optimization algorithm is then used to predict skin permeability of high molecular weight injected into the skin from a microneedle system. The effect of the optimized microneedles on blood drug concentration has been determined. The outcome of this study is useful to propose an optimum design based on different measurement (e.g., variation of skin thickness) for transdermal delivery of drugs. (c) 2008 Elsevier Ltd. All rights reserved.