Transdermal therapeutic systems for memantine delivery. Comparison of passive and iontophoretic transport.

Memantine is a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist used in the treatment of moderate to severe dementia including the symptoms of Alzheimer's disease (AD). It is administered orally but compliance, swallowing problems and the routine use of multiple medications in elderly AD patients means that an alternative route of administration would be of interest. The aim of the present study was to develop memantine hydrochloride occlusive transdermal therapeutic systems (TTS) for passive and iontophoretic delivery across the skin. Polyvinyl pyrrolidone (PVP) and a mixture with polyvinyl alcohol (PVA) were employed as polymeric matrices. The study involved the TTS characterization in addition to quantification of the memantine transport across porcine skin in vitro. The evaluation of the TTS physical properties suggested that systems were made more mechanically resistant by including PVA (6%) or high concentrations of PVP (24%). Moreover, a linear correlation was observed between the concentration of PVP and the bioadhesion of the systems. Drug delivery experiments showed that the highest transdermal flux provided by a passive TTS (PVP 24% w/w limonene) was 8.89±0.81µgcm-2h-1 whereas the highest iontophoretic transport was 46.4±3.6µgcm-2h-1. These innovative TTS would enable two dosage regimens that could lead to therapeutic plasma concentrations.

Development of antimigraine transdermal delivery systems of pizotifen malate.

The aim of this study was to develop and evaluate a transdermal delivery system of pizotifen malate. Pizotifen is frequently used in the preventive treatment of migraine, but is also indicated in eating disorders. In the course of the project, the effects of chemical enhancers such as ethanol, 1,8-cineole, limonene, azone and different fatty acids (decanoic, decenoic, dodecanoic, linoleic and oleic acids) were determined, first using a pizotifen solution. Steady state flux, diffusion and partition parameters were estimated by fitting the Scheuplein equation to the data obtained. Among the chemical enhancers studied, decenoic acid showed the highest enhancement activity, which seemed to be due to the length of its alkyl chain and unsaturation at the 9th carbon. The influence of iontophoresis and the involvement of electrotransport in said process was determined. The absorption profile obtained with iontophoresis was similar to that obtained with fatty acids and terpenes, though skin deposition of the drug was lower with the former. Transdermal delivery systems (TDS) of pizotifen were manufactured by including chemical enhancers, decenoic acid or oleic acid, and were subsequently characterized. When the results obtained with solutions were compared with those obtained with the TDS, a positive enhancement effect was observed with the latter with respect to the partitioning and diffusion of the drug across the skin. Our findings endorse the suitability of our TDS for delivering therapeutic amounts of pizotifen malate.

Transdermal absorption of memantin--effect of chemical enhancers, iontophoresis, and role of enhancer lipophilicity.

The transdermal administration of memantine may have advantages with respect to oral therapy when treating advanced stages of Alzheimer's disease. With the ultimate objective of administrating memantine through a transdermal patch, the absorption of the drug across skin was evaluated by means of in vitro permeation studies. The effect of several chemical enhancers was studied in order to enhance percutaneous absorption of the memantine. The iontophoretic transdermal transport of memantine hydrochloride using a current density of 0.5 mA/cm(2) was also investigated. Results demonstrated that pre-treatment of the skin with R-(+)-limonene, laurocapram, decenoic acid, or oleic acid produced a statistically significant increment in the transdermal flux of memantine hydrochloride with respect to the control. Iontophoresis exhibited the greatest ability to enhance the flux of drug with respect to the control; nevertheless, the results obtained with R-(+)-limonene indicate that this compound could be of great use as a percutaneous enhancer in a memantine transdermal delivery system. In this study, the relationship between enhancement activity and lipophilicity was also studied. Satisfactory correlations have been obtained between the optimum lipophilicity of the enhancer and n-octanol/water partition coefficients of drugs. This relationship is a very useful tool that could allow to reduce time and to optimize the selection of appropriate enhancers for transdermal formulations.

HPLC-UV analytical method for determination of pizotifen after in vitro transdermal diffusion studies.

Pizotifen malate is an antihistamine and serotonin inhibitor used in the preventive treatment of migraine and eating disorders. A simple, rapid, accurate and precise high-performance liquid chromatography (HPLC) method involving ultraviolet detection was validated for the quantitative analysis of pizotifen malate in samples from in vitro transdermal diffusion studies. The method was validated for specificity, linearity, accuracy, precision, limit of detection, limit of quantification and robustness. Drug stability in the solution was also determined under different conditions. Separation was carried out using a 250 × 4.0 mm Kromasil(®) C(18) column at room temperature. The detector response, fitted at 254 nm, was found to be linear in a concentration range between 0.24 and 24.0 µg/mL. The limit of detection was 0.02 µg/mL and the limit of quantification was 0.07 µg/mL. Finally, in vitro transdermal diffusion of pizotifen malate was characterized using the validated HPLC method.

Effect of iontophoresis on in vitro transdermal absorption of almotriptan.

The aim of the present work was to characterize the in vitro transdermal absorption of almotriptan through pig ear skin. The passive diffusion of almotriptan malate and its iontophoretic transport were investigated using current densities of 0.25 and 0.50mA/cm(2). In vitro iontophoresis experiments were conducted on diffusion cells with an agar bridge without background electrolytes in the donor compartment. Although both current densities applied produced a statistically significant increment with respect to passive permeation of almotriptan (p<0.01), that of 0.50mA/cm(2) proved to be the best experimental condition for increasing the transport of almotriptan across the skin. Under these experimental conditions, the transdermal flux of the drug increased 411-fold with respect to passive diffusion, reaching 264±24µg/cm(2)h (mean±SD). Based on these results, and taking into account the pharmacokinetics of almotriptan, therapeutic drug plasma levels for the management of migraine could be achieved via transdermal iontophoresis using a reasonably sized (around 7.2cm(2)) patch.

Transdermal iontophoresis of dexamethasone sodium phosphate in vitro and in vivo: effect of experimental parameters and skin type on drug stability and transport kinetics.

The aim of this study was to investigate the cathodal iontophoresis of dexamethasone sodium phosphate (DEX-P) in vitro and in vivo and to determine the feasibility of delivering therapeutic amounts of the drug for the treatment of chemotherapy-induced emesis. Stability studies, performed to investigate the susceptibility of the phosphate ester linkage to hydrolysis, confirmed that conversion of DEX-P to dexamethasone (DEX) upon exposure to samples of human, porcine and rat dermis for 7 h was limited (82.2+/-0.4%, 72.5+/-4.8% and 78.6+/-6.0% remained intact) and did not point to any major inter-species differences. Iontophoretic transport of DEX-P across dermatomed porcine skin (0.75 mm thickness) was studied in vitro as a function of concentration (10, 20, 40 mM) and current density (0.1, 0.3, 0.5 mA cm(-2)) using flow-through diffusion cells. Increasing concentration of DEX-P from 10 to 40 mM resulted in a approximately 4-fold increase in cumulative permeation (35.65+/-23.20 and 137.90+/-53.90 microg cm(-2), respectively). Good linearity was also observed between DEX-P flux and the applied current density (i(d); 0.1, 0.3, 0.5 mA cm(-2); J(DEX) (microg cm(2) h(-1))=237.98 i(d)-21.32, r(2)=0.96). Moreover, separation of the DEX-P formulation from the cathode compartment by means of a salt bridge - hence removing competition from Cl(-) ions generated at the cathode - produced a 2-fold increase in steady-state iontophoretic flux (40 mM, 0.3 mA cm(-2); 20.98+/-7.96 and 41.82+/-11.98 microg cm(-2) h(-1), respectively). Pharmacokinetic parameters were determined in Wistar rats (40 mM DEX-P; 0.5 mA cm(-2) for 5h with Ag/AgCl electrodes and salt bridges). Results showed that DEX-P was almost completely converted to DEX in the bloodstream, and significant DEX levels were achieved rapidly. The flux across rat skin in vivo (1.66+/-0.20 microg cm(-2) min(-1)), calculated from the input rate, was not statistically different from the flux obtained in vitro across dermatomed porcine skin (1.79+/-0.49 microg cm(-2) min(-1)). The results suggest that DEX-P delivery rates would be sufficient for the management of chemotherapy-induced emesis.

Development and evaluation of occlusive systems employing polyvinyl alcohol for transdermal delivery of sumatriptan succinate.

The aim of the present study was to develop a sumatriptan succinate transdermal system for applying migraine treatments efficiently and easily. For this system polyvinyl alcohol was employed as a matrix and Azone((R)) was added as a permeability enhancer. The physical characteristics, mechanical properties, and in vivo bioadhesion of the systems were evaluated, as was in vitro permeation across porcine skin. A uniform distribution of the drug in the matrix was observed, and moisture uptake values were constant. With regard to mechanical parameters, occlusive layer inclusion made the system more resistant, and no significant differences were detected with respect to other systems. Although Azone((R)) reduced the bioadhesivity of the systems, adherence to skin was maintained 24 h after application. Permeation studies showed that the systems formulated with Azone((R)) provided the highest permeability profiles for sumatriptan succinate.

Sumatriptan succinate transdermal delivery systems for the treatment of migraine.

We have successfully obtained sumatriptan transdermal systems with different polymer compositions: methyl cellulose (MC), polyvinyl pyrrolidone (PVP) and a polyvinyl pyrrolidone (PVP)-polyvinyl alcohol (PVA) mixture. The systems contained 1,2-propylenglycol (MC) or sorbitol as a plasticizer (PVP and PVP-PVA), methacrylate copolymer as an adhesive agent, and an occlusive liner. Azone (5%, w/w) was incorporated into all the systems as a percutaneous enhancer. Transdermal systems are thin, transparent and non-adhesive when in a dry state. The permeation of sumatriptan succinate across pig ear skin was studied using the systems prepared. The formulation with MC polymer produced a statistically significant increment with respect to the PVP and PVP-PVA formulations (p < 0.05). Azone incorporation into the systems produced an increment in the sumatriptan flux values of all three transdermal systems with respect to those of the controls (p < 0.05). In addition, the application of iontophoresis to the wet methyl cellulose-Azone formulation produced a much higher increase of sumatriptan transdermal flux.

Combination strategies for enhancing transdermal absorption of sumatriptan through skin.

The aim of the present work was to characterize in vitro sumatriptan transdermal absorption through human skin and to investigate the effect of chemical enhancers and iontophoresis applied both individually and in combination. A secondary objective was to compare the results obtained with those in porcine skin under the same conditions, in order to characterize the relationship between the two skin models and validate the porcine model for further research use. Transdermal flux of sumatriptan was determined in different situations: (a) after pre-treatment of human skin with ethanol, Azone (1-dodecyl-azacycloheptan-2-one), polyethylene glycol 600 and R-(+)-limonene, (b) under iontophoresis application (0.25 and 0.50 mA/cm(2)) and (c) combining chemical pre-treatment and iontophoresis at 0.50 mA/cm(2) current density. All the strategies applied enhance sumatriptan transdermal absorption. A linear relationship between the fluxes in the two skin models in the different conditions assayed can be established. The combination of both strategies, Azone and iontophoresis, proved to be the most effective of the techniques for enhancing the transdermal absorption of sumatriptan. The flux obtained with porcine skin in vitro is approximately double that obtained in human skin.

Bioadhesive monolayer film for the in vitro transdermal delivery of sumatriptan.

The work presented here aims to develop a bioadhesive monolayer film containing sumatriptan as adjuvant for the treatment of headache pain in a severe migraine attack. Permeation experiments were performed from the films prepared and from the respective solution, to evaluate the relevant permeation parameters. The effect of the penetration enhancers Transcutol, 2-pyrrolidone, and polyethylene glycol 600 was evaluated. The results obtained show that Transcutol and 2-pyrrolidone decreased sumatriptan permeation from solution, whereas a modest increase was produced by polyethylene glycol 600. The enhancers produced the same effects when they were included in the film. Compared to solution, the film showed a higher sumatriptan flux in the early times of the experiment. When the film was applied in occlusive conditions the profiles were much higher, indicating the importance of patch drying. Concerning skin retention, the bioadhesive film produced a reduction of the amount of sumatriptan remaining in the skin, but this can be advantageous in the control of drug input, since it reduces the reservoir effect in the skin and allows for an immediate interruption of drug input when the patch is removed.

Iontophoretic transdermal delivery of sumatriptan: effect of current density and ionic strength.

Iontophoretic transdermal delivery of sumatriptan was investigated in vitro. Among the conditions tested, 0.25 mA/cm2 and low ionic strength (NaCl 25 mM) was the best experimental condition to increase its transport across the skin. The flux increased 385-fold respective to passive diffusion, thus resulting in a transdermal flux of sumatriptan of 1273+/-83 nmol/cm2 h.

Effect of chemical enhancers on the in vitro percutaneous absorption of sumatriptan succinate.

The effects of percutaneous enhancers on the transdermal absorption of sumatriptan succinate were investigated by in vitro permeation studies. Pretreatment of porcine skin with ethanol (vehicle), polyethylene glycol 600, Span 20, oleic acid, R-(+)-limonene, alpha-bisabolol and 1,8-cineole (at 5% in ethanol, w/w) produced in all cases an increase in the flux of sumatriptan. The amount of sumatriptan retained in the skin was also determined. Ethanol has showed a low but significant increment on the drug transdermal flux. Treatment of the skin with alpha-bisabolol shows the same enhancer effect than ethanol. Span 20, oleic acid, and polyethylene glycol 600 have shown a moderate enhancing activity on transdermal flux of sumatriptan. R-(+)-limonene showed the greatest ability to enhance the flux of sumatriptan.