Transdermal drug delivery by coated microneedles: geometry effects on drug concentration in blood

Drug administration through transdermal delivery is restricted by the top layer of skin, the stratum corneum. One possible solution to overcome the barrier function of the stratum corneum is to employ microneedle arrays. However, detailed theoretical models relating drugcoated microneedles and their geometry to the drug concentration in the blood are limited. This paper aims to address this issue by examining the blood concentration profiles for a model drug, insulin, that has been administered via coated microneedles. A mathematical model is introduced and applied to predict theoretical blood concentrations. Furthermore, the insulin concentration in blood is calculated for a range of different microneedle shapes and dimensions to identify the most effective geometry. The results indicate that the optimum mic r2o0needle geometry in terms of maximimizing insulin concentration was a rocket shaped needle that has a constant tip angle of 90º. Also, it has been found that the number of microneedles in an array is the most significant factor in determining maximum insulin concentration in the blood (Cb,max).