Response surface method: a novel strategy to optimize iontophoretic transdermal delivery of thyrotropin-releasing hormone

Iontophoretic skin permeation of peptides: an investigation into the influence of molecular properties, iontophoretic conditions and formulation parameters

The transdermal route offers advantages for delivery of peptides and proteins. However, these polar and large molecules do not permeate the skin barrier well. Various enhancement methods have been employed to address this problem. Iontophoresis is one of the methods that shows promise but its application to peptide delivery has yet to be fully explored. This study investigates the effects of different molecular properties and iontophoretic conditions on the skin permeation of peptides. In this study, the permeation of alanine-tryptophan dipeptide (MW 276 Da), alanine-alanine-proline-valine tetrapeptide (MW 355 Da), Argireline® (Acetyl hexapeptide-3, MW 889 Da) and Triptorelin acetate (decapeptide, MW 1311 Da) through excised human skin under passive or iontophoretic current of 0.4 mA was investigated. The effects of pH change (3.0-7.4, to provide different net negative, neutral, and positive charges) to the peptide, donor concentration (1-10 mg/ml), background electrolyte (34-137 mM NaCl and/or 5-20 mM HEPES) and current direction (anodal vs cathodal) were also studied. Peptides were analysed by high-performance liquid chromatography or liquid scintillation counting. Iontophoresis led up to a 30 times increase in peptide permeation relative to passive permeation for the peptides. Electroosmosis was an important determinant of the total flux for the high molecular weight charged peptides. Electrorepulsion was found to be considerable for low molecular weight charged moieties. Permeation was decreased at lower pH, possibly due to decreased electroosmosis. Results also showed that 10 times increase in donor peptide concentration increases permeation of peptides by about 2-4 times and decreases iontophoretic permeability coefficients by about 2.5-5 times. The addition of extra background electrolyte decreased the iontophoretic permeation coefficient of peptides by 2-60 times. This study shows that iontophoretic permeation of peptides is affected by a number of parameters that can be optimized for effective transdermal peptide delivery.

Effects of bone density alterations on strain patterns in the pelvis: Application of a finite element model

Insufficiency fractures occur when physiological loads are applied to bone deficient in mechanical resistance. A better understanding of pelvic mechanics and the effect of bone density alterations could lead to improved diagnosis and treatment of insufficiency fractures. This study aimed to develop and validate a subject-specific three-dimensional (3D) finite element (FE) model of a pelvis, to analyse pelvic strains as a function of interior and cortical surface bone density, and to compare high strain regions with common insufficiency fracture sites. The FE model yielded strong agreement between experimental and model strains. By means of the response surface method, changes to cortical surface bone density using the FE model were found to have a 60 per cent greater influence compared with changes in interior bone density. A small interaction was also found to exist between surface and interior bone densities (< 3 per cent), and a non-linear effect of surface bone density on strain was observed. Areas with greater increases in average principal strains with reductions in density in the FE model corresponded to areas prone to insufficiency fracture. Owing to the influence of cortical surface bone density on strain, it may be considered a strong global (non-linear) indicator for insufficiency fracture risk.

Application of artificial neural networks in the design of controlled release drug delivery systems

Controlled release drug delivery systems offer great advantages over the conventional dosage forms. However, there are great challenges to efficiently develop controlled release drug delivery systems due to the complexity of these delivery systems. Traditional statistic response surface methodology (RSM) is one of the techniques that has been employed to develop and formulate controlled release dosage forms. However, there are some limitations to the RSM technique. Hence, another technique called artificial neural networks (ANN) has recently gained wide popularity in the development of controlled release dosage forms. In this review, the basic ANN structure, the development of the ANN model and an explanation of how to use ANN to design and develop controlled release drug delivery systems are discussed. In addition, the applications of ANN in the design and development of controlled release dosage forms are also summarized in this review.

Prediction of drug release profiles using an intelligent learning system: an experimental study in transdermal iontophoresis

This paper investigates the use of a neural-network-based intelligent learning system for the prediction of drug release profiles. An experimental study in transdermal iontophoresis (TI) is employed to evaluate the applicability of a particular neural network (NN) model, i.e. the Gaussian mixture model (GMM), in modeling and predicting drug release profiles. A number of tests are systematically designed using the face-centered central composite design (CCD) approach to examine the effects of various process variables simultaneously during the iontophoresis process. The GMM is then applied to model and predict the drug release profiles based on the data samples collected from the experiments. The GMM results are compared with those from multiple regression models. In addition, the bootstrap method is used to assess the reliability of the network predictions by estimating confidence intervals associated with the results. The results demonstrate that the combination of the face-centered CCD and GMM can be employed as a useful intelligent tool for the prediction of time-series profiles in pharmaceutical and biomedical experiments.

Drug delivery across the skin

For more than two decades, researchers have attempted to find a way to use the skin as a portal of entry for drugs in order to overcome problems associated with traditional modes of drug administration. This has been a complicated task due to the highly effective barrier properties of the skin. In order to deliver drugs through the skin, most compounds require various degrees of permeation enhancement. Classic enhancement methods focused primarily on chemical enhancement or modulation of interactions between the drug and the vehicle. More recent research makes use of innovative vesicular carriers, electrically assisted delivery and various microinvasive methods, some incorporating technologies from other fields. These new and exciting methods for drug delivery are already increasing the number and quality of dermal and transdermal therapies. This review discusses the different types of permeation enhancement, both classic and innovative, and summarises the current strengths and shortcomings in the field with an emphasis on those that have led to products on the market or in the pipeline.