Electrically modulated transdermal delivery of fentanyl

Multiscale Modeling of Skin Electroporation

Human skin, the largest external organ of the body, provides a selective barrier to therapeutics applied topically. The molecules having specific chemical and physical properties can only penetrate the deeper layer of the skin. However, the lag time for reaching a steady state in the deeper layer is generally of the order of hours. In order to deliver higher-molecular-weight, charged, and hydrophilic therapeutics in the deeper layer, the skin barrier must be breached. Electroporation is one of the methods used to breach the skin barrier for enhancement of drug permeation and reduction of lag time. However, the underlying mechanism responsible for the enhancement of drug permeation is not well understood. In this study, a multiscale model of skin electroporation is developed by connecting molecular phenomena to a macroscopic model. At the atomic scale, molecular dynamics simulations of the lipid matrix of the human stratum corneum (SC) were performed under the influence of an external electric field. The pores get formed during the electroporation process and the transport properties (diffusivity) of drug molecules are computed. The diffusion coefficient obtained during electroporation was found to be higher than passive diffusion. However, this alone could not explain the multifold increase in the drug flux on application of an electric field as observed in the experiments. Hence, a finite element method (FEM) model of the skin SC is also developed. The release of fentanyl through this model is compared with the available experimental results. Both experimental and simulated results of pore formation on application of an electric field and many folds' increase in drug flux are comparable. Once validated, the framework was used for the design of skin electroporation experiments (in silico) by changing the electric pulse parameters such as voltage, pulse duration, and number of pulses. This multiscale modeling framework provides valuable insight at the molecular and macroscopic levels to design the electroporation experiments. The framework can be utilized as a design tool for skin electroporation applications.

Efectos del cátodo y del ánodo de la corriente directa en los cambios de fuerza de prensión palmar: valoración a través de dinamometría

RESUMEN El objetivo de este trabajo es investigar los efectos polares de la corriente directa sobre la fuerza muscular, evaluada con dinamómetro manual. Los valores de la fuerza muscular en kilogramos fueron comparados antes y después del procedimiento en 3 grupos (Anodo, Catodo y Control). El diseño es Ensayo Clínico Aleatorio controlado. La investigación se realizó el Laboratorio de Fisioterapia de la Universidad Andrés Bello (Escuela de Kinesiología Santiago). El estudio se llevó a cabo con ciento cincuenta participantes voluntarios sanos. La intervención consistió en la aplicación de una sesión de corriente directa a una intensidad de 2mA por 12 minutos con un electrodo de 48cm2 (dosis 24mA.min y densidad de corriente 0,04mA/cm2). La diferencia entre los grupos radicaba en la estimulación con el cátodo o ánodo. La aplicación de la corriente se realizaba luego de la evaluación dinamométrica inicial. Cómo outcome principal se estimó la diferencia de Fuerza Máxima de prensión palmar (Kg). Esta se obtuvo de la diferencia del mejor valor de fuerza máxima pre intervención con el mejor valor de fuerza máxima post intervención. Los resultados indican que no existen cambios estadísticamente significativos en los grupos intervenidos (p valor = 0,88) al comparar las diferencias de fuerzas máximas (FMdif). Sin embargo, se aprecia una mínima mejora de la fuerza al comparar los grupos sólo considerando hombres del grupo cátodo (p valor = 0,94, y leve disminución al comparar sólo para mujeres del grupo ánodo (p valor = 0,91).Cómo conclusión se destaca que aparentemente la corriente directa no generaría mayores cambios en la fuerza de prensión manual luego de una sesión de intervención sobre el antebrazo. Sin embargo, existen variaciones positivas de fuerza en hombres del grupo cátodo y negativas mujeres del grupo ánodo al analizarlos independientemente, aunque estas modificaciones no resultan estadísticamente significativas.

Fentanyl Iontophoretic Transdermal System

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Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. If you would like information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800-322-4349. The October 2006 monograph topics are levetiracetam injection, idursulfase, certolizumab pegol, telbivudine, and etonogestrel implant. The DUE is levetiracetam injection.

Dermal, subdermal, and systemic concentrations of granisetron by iontophoretic delivery

PURPOSE

The purpose of this work was to demonstrate the iontophoretic delivery of granisetron hydrochloride by novel, self-contained iontophoretic patches and to determine the subcutaneous and dermal absorption kinetics using microdialysis.

METHODS

In vitro iontophoretic delivery of granisetron hydrochloride was evaluated at 5, 10, or 20 mg/ml concentrations of donor using Franz diffusion cells and hairless rat skin as a membrane. In vivo studies were performed in hairless rats. Animals received either subcutaneous or dermal microdialysis probes and iontophoretic patches filled with drug formulation were applied on the abdominal area such that the probe lies below the anode chamber. Blood and microdialysate samples were collected at different time intervals. Intravenous administration of granisetron was also done to determine the basic pharmacokinetic parameters.

RESULTS

Iontophoretic patches delivered current constantly throughout the patch application. The patches delivered granisetron hydrochloride at a rate of 14.91+/-4.53 microg/min/kg. Similar concentrations of granisetron hydrochloride in dermal and subcutaneous tissue were observed. Depot formation was identified in the subcutaneous and dermal profiles, indicating that subcutaneous structures are also responsible for the depot formation of the drug in the dermis.

CONCLUSION

The patches successfully delivered granisetron hydrochloride by iontophoresis and depot formation was observed in the dermal and subcutaneous structures in the skin.

Molecular change signal-to-noise criteria for interpreting experiments involving exposure of biological systems to weakly interacting electromagnetic fields

We describe an approach to aiding the design and interpretation of experiments involving biological effects of weakly interacting electromagnetic fields that range from steady (dc) to microwave frequencies. We propose that if known biophysical mechanisms cannot account for an inferred, underlying molecular change signal-to-noise ratio, (S/N)gen, of a observed result, then there are two interpretation choices: (1) there is an unknown biophysical mechanism with stronger coupling between the field exposure and the ongoing biochemical process, or (2) the experiment is responding to something other than the field exposure. Our approach is based on classical detection theory, the recognition that weakly interacting fields cannot break chemical bonds, and the consequence that such fields can only alter rates of ongoing, metabolically driven biochemical reactions, and transport processes. The approach includes both fundamental chemical noise (molecular shot noise) and other sources of competing chemical change, to be compared quantitatively to the field induced change for the basic case that the field alters a single step in a biochemical network. Consistent with pharmacology and toxicology, we estimate the molecular dose (mass associated with field induced molecular change per mass tissue) resulting from illustrative low frequency field exposures for the biophysical mechanism of voltage gated channels. For perspective, we then consider electric field-mediated delivery of small molecules across human skin and into individual cells. Specifically, we consider the examples of iontophoretic and electroporative delivery of fentanyl through skin and electroporative delivery of bleomycin into individual cells. The total delivered amount corresponds to a molecular change signal and the delivery variability corresponds to generalized chemical noise. Viewed broadly, biological effects due to nonionizing fields may include animal navigation, medical applications, and environmental hazards. Understanding necessary conditions for such effects can be based on a unified approach: quantitative comparison of the estimated chemical change due to a particular electromagnetic field exposure to that due to competing influences, with both estimates based on a biophysical mechanism model within the context of a model of a biological system.

Factorial design approach to evaluate interactions between electrically assisted enhancement and skin stripping for delivery of tacrine

The objective of this work was to study the mechanisms of action of iontophoresis and electroporation and their interaction effects on delivery of tacrine hydrochloride in vitro across intact and stripped rat skin. Experiments were done according to a full factorial design, to quantify the effects of iontophoresis (X1), electroporation (X2) and stripped skin (X3) alone and in combination on cumulative drug delivery at 6 h. Mathematical model eliciting the main effects of the factors and their interaction on cumulative tacrine delivery in 6 h shows that all three techniques examined alone have a positive impact on the permeation of tacrine, the greatest enhancement in delivery achieved by iontophoresis. However, iontophoresis in combination with electroporation or skin stripping yielded no improvement in delivery compared to iontophoresis alone. The most significant enhancement is seen when all three methods of assisted delivery are done in combination. Iontophoresis appears to control drug delivery to the exclusion of other enhancement methods. Electroporation appears to cause formation of a large depot of tacrine in the skin.