Characterization of the permselective properties of rabbit skin during transdermal iontophoresis

doi:10.1002/jps.10405

Journal of Pharmaceutical Sciences

Volume 92, Issue 7, July 2003, Pages 1482-1488

https://doi.org/10.1002/jps.10405 Get rights and content

ABSTRACT:

The use of iontophoresis to enhance transdermal transport of drugs necessitates further investigations on the membrane used to simulate human skin because one of the transport mechanisms involved, electroosmosis, strictly depends on the properties of the skin (i.e., its isoelectric point, IP). The aim of this work was to characterize rabbit ear skin permselectivity by measuring the sodium transport number at different pH values. This method allowed us to estimate the skin IP. To confirm the validity of the method, mannitol flux was measured. In addition, the sodium transport number method was applied to the study of human skin and a model drug iontophoretic flux through rabbit and human skin was evaluated. The results indicate that rabbit ear skin behaves as a permselective membrane, with an IP between 2 and 3. The same result was obtained using human skin. The mannitol flux data confirm that the direction of electroosmotic flow at physiological pH is in the anode-to-cathode direction. Finally, permeation experiments performed with a model drug showed that the relative electroosmotic and electrorepulsive contributions to the total flux are the same for human and rabbit skin. It can be concluded that rabbit ear skin is a suitable model for the study of iontophoretic permeation of drugs.

Section snippets

INTRODUCTION

Transdermal administration is considered as a valid alternative to the oral and parenteral routes in medicine today. The first step in the evaluation of a new transdermal formulation/molecule is that of in vitro permeation studies. The reference barrier for these studies is human skin, although its limited availability often necessitates the use of other skin models. Artificial and natural membranes have been investigated as models for human skin.1., 2., 3. Hairless mouse is the most common and

Materials

Lidocaine hydrochloride (fw = 270.2, pK_a = 7.9) was a gift from Lisapharma (Erba, Co, Italy). N-[2-Hydroxyethyl] piperazine-N′-[2-ethanesulfonic acid] (HEPES), as well as D-mannitol and silver chloride that were used for the preparation of the electrodes, were purchased from Sigma Chemical (St. Louis, MO). One-millimeter diameter silver wires (purity, 99.9%) were used for electrode preparation. Disodium hydrogen phosphate dodecahydrate, potassium dihydrogen phosphate, and sodium chloride were

Sodium Transport Number

The $t_{{Na}^{+}}$ parameter, representing the fraction of current carried by sodium ions when chloride is present, is ∼0.4 in free aqueous solution.¹⁴ A preferential transport of cations occurs in the presence of a membrane supporting a net negative charge,¹⁴ which causes an increase in the transport number value for cations. In contrast, the value through a neutral membrane should be equal to the value in free aqueous solution.

To evaluate the reliability of the method, $t_{{Na}^{+}}$ was measured at different pH

CONCLUSIONS

From the results obtained in this work, it can be concluded that rabbit ear skin behaves as a permselective membrane, with an IP between 2 and 3. The data on mannitol flux confirm that the direction of electroosmotic flow at physiological pH is in the anode-to-cathode direction. Permeation experiments performed using lidocaine as a model drug show that, despite the differences in the total iontophoretic flux, the relative electroosmotic and electrorepulsive contributions are almost the same for

Acknowledgements

This work was supported by a grant from the University of Parma (Progetto Ricercatori Singoli). We are extremely grateful for the helpful suggestions of Dr. Yogeshvar Kalia (University of Geneva, CH).

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In-vitro characterization of buccal iontophoresis: The case of sumatriptan succinate
2016, International Journal of Pharmaceutics
Citation Excerpt :
The sodium transport number (tNa+) is defined as the fraction of charge transported by sodium ions. Its value, when a current is applied across a neutral membrane, is the same as in free solution, namely approx. 0.4 (Burnette and Ongipattanakul, 1987; Nicoli et al., 2003). From the measurement of sodium transport number at different pH values it is possible to evaluate the isoelectric point of the tissue, i.e. the pH value at which the membrane carries no net charge: above this value the membrane is negatively charged, below this value the membrane is positively charged.
Buccal administration of sumatriptan succinate might be an interesting alternative to the present administration routes, due to its non-invasiveness and rapid onset of action, but because of its low permeability, a permeation enhancement strategy is required. The aim of this work was then to study, in-vitro, buccal iontophoresis of sumatriptan succinate.
Permeation experiments were performed in-vitro across pig esophageal epithelium, a recently proposed model of human buccal mucosa, using vertical diffusion cells. The iontophoretic behavior of the tissue was characterized by measuring its isoelectric point (Na⁺ transport number and the electroosmotic flow of acetaminophen determination) and by evaluating tissue integrity after current application.
The results obtained confirm the usefulness of pig esophageal epithelium as an in-vitro model membrane for buccal drug delivery. The application of iontophoresis increased sumatriptan transport, proportionally to the current density applied, without tissue damage: electrotransport was the predominant mechanism.
Integrating the results of the present work with literature data on the transport of other molecules across the buccal mucosa and across the skin, we can draw a general conclusion: the difference in passive transport across buccal mucosa and across the skin is influenced by permeant lipophilicity and by the penetration pathway.
Finally, buccal iontophoretic administration of sumatriptan allows to administer 6 mg of the drug in 1 h, representing a promising alternative to the current administration routes.
Mathematical models to describe iontophoretic transport in vitro and in vivo and the effect of current application on the skin barrier
2013, Advanced Drug Delivery Reviews
The architecture and composition of the stratum corneum make it a particularly effective barrier against the topical and transdermal delivery of hydrophilic molecules and ions. As a result, different strategies have been explored in order to expand the range of therapeutic agents that can be administered by this route. Iontophoresis involves the application of a small electric potential to increase transport into and across the skin. Since current flow is preferentially via transport pathways with at least some aqueous character, it is ideal for hydrosoluble molecules containing ionisable groups. Hence, the physicochemical properties that limit partitioning and passive diffusion through the intercellular lipid matrix are beneficial for electrically-assisted delivery. The presence of fixed ionisable groups in the skin (pI 4–4.5) means that application of the electric field results in a convective solvent flow (i.e., electroosmosis) in the direction of ion motion so as to neutralise membrane charge. Hence, under physiological conditions, cation electrotransport is due to both electromigration and electroosmosis—their relative contribution depends on the formulation conditions and the physicochemical properties of the permeant. Different mathematical models have been developed to provide a theoretical framework in order to explain iontophoretic transport kinetics. They usually involve solutions of the Nernst–Planck equation – using either the constant field (Goldman) or electroneutrality (Nernst) approximations – with or without terms for the convective solvent flow component. Investigations have also attempted to elucidate the nature of ion transport pathways and to explain the effect of current application on the electrical properties of the skin—more specifically, the stratum corneum. These studies have led to the development of different equivalent circuit models. These range from simple parallel arrangements of a resistor and a capacitor to the inclusion of the more esoteric “constant phase element”; the latter provides a better mathematical description of the “non-ideal” behaviour of skin impedance. However, in addition to simply providing a “mathematical” fit of the observed data, it is essential to relate these circuit elements to biological structures present in the skin. More recently, attention has also turned to what happens when the permeant crosses the epidermis and reaches the systemic circulation and pharmacokinetic models have been proposed to interpret data from iontophoretic delivery studies in vivo. Here, we provide an overview of mathematical models that have been proposed to describe (i) the effect of current application on the skin and the implications for potential iontophoretic transport pathways, (ii) electrotransport kinetics and (iii) the fate of iontophoretically delivered drugs once they enter the systemic circulation.
Amikacin reverse iontophoresis: Optimization of in vitro extraction
2013, International Journal of Pharmaceutics
Citation Excerpt :
The result obtained, illustrated in Fig. 4, confirms the ability of AK to reduce AM iontophoretic transport. The electroosmotic flow in the absence of AK (calculated from AM flux and AM donor concentration according to (Marro et al., 2001)), resulted 2.63 ± 0.90 μl cm−2 h−1, in agreement with previously obtained data on rabbit ear skin (Nicoli et al., 2003). This value was reduced to 1.51 ± 0.76 μl cm−2 h−1 by the presence of AK in the donor solution (p < 0.05).
The aim of this work was to optimize amikacin reverse iontophoretic extraction across the skin in vitro, for non-invasive drug monitoring. Reverse iontophoresis experiments were performed using vertical diffusion cells. The lower chamber, simulating body fluids, contained amikacin bisulphate and acetaminophen, as marker for electroosmosis, while the upper chamber was filled with the appropriate extraction solution. The effect of concentration of amikacin in the dermal bathing solution and the effect of extraction solution composition and pH were studied.
The results show that the extraction of amikacin was independent of pH and always in the anode-to-cathode direction, in agreement with the positive charge of the drug. The presence of amikacin in the bathing solution did not modify acetaminophen extraction at pH 4.0, while the extraction was reduced at pH 8.0. In conclusion, amikacin can be extracted across the skin in vitro by reverse iontophoresis. Owing to the charge of the molecule, extraction takes place at the cathode. Using acetaminophen as neutral marker, it was shown that amikacin can interact with the skin and alter its permselectivity at pH 8.0.
Synthesis, hydrolysis, and skin retention of amino acid esters of α-tocopherol
2009, Journal of Pharmaceutical Sciences
Citation Excerpt :
The derivatives were characterized and tested for sensitivity to chemical and enzymatic hydrolysis. The skin retention and metabolism of the new pro-vitamins was determined in vitro, using rabbit ear skin, which has a permeability comparable to human skin17, 18 (ratio rabbit/human skin permeability 1.2 and 1.6 for lidocaine and thiocolchicoside, respectively). α-Tocopherol (m.w. 430.72, yellow oil), α-tocopheryl acetate, as well reactants and catalysts, were purchased by Sigma (Sigma Chemical, St. Louis, MO), while all amino acids and anhydrous solvents were obtained by Fluka (Fluka Chemie, Buchs, Switzerland).
The aim of this work was to synthesize new pro-vitamins of α-tocopherol (VE) able to release another moiety such as an amino acid, in order to obtain a combined antioxidant and moisturizing effect upon topical application. The new derivatives were characterized and tested for sensitivity to chemical and enzymatic hydrolysis. Lipophilicity was estimated using Log capacity factor and skin retention was determined in vitro, using rabbit ear skin as barrier. Five molecules were synthesized using L-proline, L-serine, L-tyrosine, L-asparagine, and L-citrulline as amino acidic moiety. All pro-vitamins showed similar or lower lipophilicity than α-tocopheryl acetate (VEAc), taken as reference, and similar stability in aqueous solutions. All pro-vitamins showed to be sensitive to enzymatic hydrolysis. None of the pro-vitamins crossed the skin in significant amounts, whereas they accumulated into the skin, in both the dermis and the epidermis. They are more hydrophilic and more water-soluble than the currently used acetate. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association.
Innovative formulations for the delivery of levothyroxine to the skin
2009, International Journal of Pharmaceutics
The aim of this work was to realize innovative transdermal formulations containing sodium levothyroxine in view of topical administration. Permeation experiments were performed in vitro, using rabbit ear skin as barrier. At the end of the permeation experiments levothyroxine retained in the skin was extracted and quantified by HPLC. Formulations tested were microemulsions and transdermal films. Microemulsions containing isopropyl myristate and isobutanol were shown to be able to increase levothyroxine solubility by the inclusion in reverse micelles. However, the inclusion in reversed micelles reduced the drug release to a significant extent, and consequently skin retention, compared to aqueous solutions. When the microemulsion was included in the transdermal film, drug retention was increased, probably for the enhancer effect of its excipients. The transdermal film proposed in this work could be an interesting alternative to semisolid formulations for the ease of use and the control in the amount of active applied. Additional benefit can be obtained if the film is used in occlusive conditions.
Recent advances on transdermal iontophoretic drug delivery and non-invasive sampling
2009, Journal of Drug Delivery Science and Technology
Transdermal iontophoresis has become a mature drug delivery technique; iontophoretic devices have been approved by the regulatory agencies for the delivery of fentanyl and lidocaine. Active research investigates other applications for local and systemic drug administration; namely anti-inflammatory drugs, anaesthetics, analgesics, antiviral agents, peptides, proteins, drugs used in photodynamic therapy and to treat Parkinson’s disease and migraine. Its potential for non-invasive sampling has found applications in glucose monitoring, therapeutic drug monitoring and pharmacokinetic profiling. The last eight years have brought a better understanding on the mechanisms and pathways of transport during transdermal iontophoresis, on the selection of drug candidates and the formulation of iontophoretic vehicles. Local effects of iontophoresis are typically moderate to mild oedema and erythema, tingling and itching sensations, and transient elevations of the skin temperature and transepidermal water loss. Iontophoresis is considered a safe, non-invasive and effective way of delivering transdermally judiciously chosen drugs.

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Research ArticlesCharacterization of the permselective properties of rabbit skin during transdermal iontophoresis

ABSTRACT:

Section snippets

INTRODUCTION

Materials

Sodium Transport Number

CONCLUSIONS

Acknowledgements

Int J Pharm

J Invest Dermatol

J Control Release

J Pharm Sci

Int J Pharm

Adv Drug Delivery Rev

J Controlled Release

J Controlled Release

J Pharm Sci

Adv Drug Deliv Rev

Biological models to study skin permeation

Animal models for transdermal drug delivery

Methods Find Exp Clin Pharmacol

Limitations of hairless mouse skin as a model for in vitro permeation studies through human skin: Hydration damage

J Invest Dermatol

Animal models for percutaneous absorption

Pig ear skin as an in-vitro model for human skin permeability

J Pharm Pharmacol

Research Articles
Characterization of the permselective properties of rabbit skin during transdermal iontophoresis