0000000000424641
AUTHOR
Arto Urtti
Controlled transdermal iontophoresis by ion-exchange fiber
The objective of this study was to assess the transdermal delivery of drugs using iontophoresis with cation- and anion-exchange fibers as controlled drug delivery vehicles. Complexation of charged model drugs with the ion-exchange fibers was studied as a method to achieve controlled transdermal drug delivery. Drug release from the cation-exchange fiber into a physiological saline was dependent on the lipophilicity of the drug. The release rates of lipophilic tacrine and propranolol were significantly slower than that of hydrophilic nadolol. Permeation of tacrine across the skin was directly related to the iontophoretic current density and drug concentration used. Anion-exchange fiber was te…
Interpretation of Ocular Melanin Drug Binding Assays. Alternatives to the Model of Multiple Classes of Independent Sites
Melanin has a high binding affinity for a wide range of drugs. The determination of the melanin binding capacity and its binding affinity are important, e.g., in the determination of the ocular drug distribution, the prediction of drug effects in the eye, and the trans-scleral drug delivery. The binding parameters estimated from a given data set vary significantly when using different isotherms or different nonlinear fitting methods. In this work, the commonly used bi-Langmuir isotherm, which assumes two classes of independent sites, is confronted with the Sips isotherm. Direct, log-log, and Scatchard plots are used, and the interpretation of the binding curves in the latter is critically a…
Drug Distribution to Retinal Pigment Epithelium: Studies on Melanin Binding, Cellular Kinetics, and Single Photon Emission Computed Tomography/Computed Tomography Imaging
Melanin binding is known to affect the distribution and elimination of ocular drugs. The purpose of this study was to evaluate if the extent of drug uptake to primary retinal pigment epithelial (RPE) cells could be estimated based on in vitro binding studies with isolated melanin and evaluate the suitability of single photon emission computed tomography/computed tomography (SPECT/CT) in studying pigment binding in vivo with pigmented and albino rats. Binding of five compounds, basic molecules timolol, chloroquine, and nadolol and acidic molecules methotrexate and 5(6)-carboxy-2',7'-dichlorofluorescein (CDCF), was studied using isolated melanin from porcine choroid-RPE at pH 5.0 and 7.4. The…