Modulation of electroosmosis and flux through skin: effect of propylene glycol

The effect of propylene glycol (PG) on transdermal flux under current was investigated using conventional in vitro iontophoresis methodology. The results were evaluated to explain how PG affects the electroosmotic volume flow (EVF) and electromigrational flux through skin. As a marker molecule for the direction and magnitude of EVF, a non-charged neutral molecule, acetaminophen (AAP), was used. At pH 7.4, the direction of EVF was from anode to cathode. During anodal and cathodal current application, PG decreased AAP flux and this decrease was proportional to the concentration of PG, indicating that the presence of PG in the medium decreased the EVF. This decrease is likely due to the decrease in dielectric constant of the medium and the increases in medium viscosity by the addition of PG. The increase in AAP solubility and the viscosity of the medium by PG may also contribute to the decrease in diffusional flux. The magnitude of EVF was estimated to be about 4.2 μl/cm² h. The effect of PG on the flux of a positively charged drug, donepezil hydrochloride (DH), was further investigated using pH 4.6 phosphate buffer solution. The permselectivity of skin in this solution was also investigated and revealed that the isoelectric point of hairless mouse skin is higher than pH 4.6. Anodal delivery showed much higher flux than cathodal and passive flux, indicating that electromigration is playing the major role for DH flux. As the concentration of PG increased, anodal flux of DH decreased. The main reason for this decrease in electromigration is likely due to the increase in medium viscosity. These results and discussions clearly suggest that the incorporation of frequently used organic cosolvents and penetration enhancers into the iontophoretic formulation should be carefully chosen with a thorough investigation for their effect on flux. Overall, these results provided further mechanistic insights into the role of electroosmosis and electromigration in flux across skin, and how they can be modulated by organic cosolvent, PG.     

Effect of pH and penetration enhancers on electroosmotic flow and flux through skin

We have investigated the effect of pH and four penetration enhancers on the electroosmotic volume flow (EVF) and flux through skin to get more detailed understanding of this phenomenon and its effect on flux. The results were evaluated in relation EVF and the permeability change by current induced skin damage. At pH 7.4, we have confirmed that the direction of convective solvent flow is from anode to cathode. At pH 4.0, no permselectivity was observed and it seems that this pH is close to the isoelectric point of skin. At pH 3.0, the permselectivity of skin is reversed. From the difference in flux between just before (47 μg/cm² h) and after (32 μg/cm² h) cathodal current-off, the magnitude of EVF is estimated to be smaller than 1.5 μl/cm² h, if we consider the recovery of skin to a lower permeability after current-off. At pH 7.4, Oleic acid (OA) and propylene glycol monolaurate (PGML) increased the passive flux markedly. Synergistic effect in flux between OA and current was observed for both anodal and cathodal current. The use of isopropyl myristate (IPM) in combination with anodal current resulted in reduced flux when compared to the flux of anodal current alone. Cathodal flux of OA or PGML treated skin increased continuously until the current was off. However, to the contrary of our expectation, flux decreased after current-off. We think this is mainly due to the recovery of damaged skin (flux decreasing effect), though the disappearance of EVF may slightly increase the flux. For IPM and propylene glycol, the combination of enhancer with cathodal current inhibited the flux, similar to that observed for anodal delivery. Overall, these results provide further information on the role of electroosmosis and the effect of penetration enhancers in combination with current on flux through skin.     

Cutaneous metabolism of a dipeptide influences the iontophoretic flux of a concomitant uncharged permeant

Passive and iontophoretic transport of the model dipeptide tyrosine-phenylalanine (TyrPhe) that is subject to cutaneous metabolism and the uncharged glucose derivative benzyl-2-acetamido-2-deoxy-alpha-d-glucopyranoside (BAd-alpha-Glc) used as electroosmosis marker through heat-separated human epidermis was investigated in vitro. TyrPhe and BAd-alpha-Glc were used separately and in combination in order to determine their interaction in terms of permeability and the influence of skin metabolism of TyrPhe on permeation rate and tissue retention of itself and of BAd-alpha-Glc. TyrPhe was chemically and electrochemically stable but underwent considerable degradation in the epidermis under reflection boundary conditions with generation of degradation products tyrosine (Tyr) and phenylalanine (Phe) confirming cutaneous metabolism of TyrPhe in heat-separated human epidermis, which was more pronounced at pH 4.5 than at pH 3.0. As a result, no reproducible epidermis permeation of TyrPhe at pH 3 and no permeation at all at pH 4.5 was measured regardless of the presence of BAd-alpha-Glc, accompanied by increased levels of Tyr and Phe compared to blank runs. Low temperature (4 degrees C) at both pH values and addition of o-phenanthroline at pH 3 but not at pH 4.5 yielded reproducible TyrPhe permeation and blank, i.e., endogenous levels of Tyr and Phe evidencing inhibition of degradation. Constant voltage anodal iontophoresis marginally reduced BAd-alpha-Glc flux at pH 3 and 4.5 compared to the passive flux. In combination with TyrPhe, iontophoretic flux of BAd-alpha-Glc was increased markedly compared to the passive one when TyrPhe was metabolized in the tissue, while no such increase was observed when TyrPhe metabolism was inhibited. The increase of BAd-alpha-Glc iontophoretic flux was accompanied by a considerable decrease of the BAd-alpha-Glc amount retained in the epidermis. The presence of the generated Tyr and Phe, therefore, appears to be related to a decrease of the BAd-alpha-Glc amount retained in the epidermis upon application of an electrical voltage and an enhancement of its iontophoretic flux. Thus, an interaction between the concurrent permeants at the level of tissue retention induced by metabolism can influence the apparent iontophoretic permeation.     

Physicochemical considerations in the iontophoretic delivery of a small peptide: in vitro studies using arginine vasopressin as a model peptide.

Transdermal iontophoresis (TI) is a physical enhancement technique to facilitate the delivery of primarily charged molecules across the skin. TI of peptides is influenced by a complex interplay of several factors and one of the main issues in optimizing iontophoretic delivery of peptides is to improve the transport efficiency.From this perspective, this study investigates the effect of the physicochemical parameters on the TI of a peptide arginine vasopressin (AVP). The permeation of AVP showed a linear dependence on the concentration of drug in the donor medium. The iontophoretic flux of AVP was strongly influenced by the pH of the donor solution. Increasing the pH from 5.16 to 7.4 resulted in a decrease in the enhancement ratio by 4.5 times. When the ionic strength was increased by varying the amount of NaCl from 0.05 to 0.25 M the flux was found to decrease by 3.2 times. Replacing normal saline in the receptor compartment by HEPES buffer showed a resultant four times increase in drug permeation. The physiochemical parameters of the donor medium play a significant role in the efficiency of drug delivery by iontophoresis for a small peptide like AVP. Though electrorepulsion would be expected to be the main mechanism involved in the movement of charged molecules across the skin by iontophoresis, for peptides in the molecular weight range of AVP, other associated secondary effects like osmosis, electroosmosis and counter ion flow may also play a significant role in transport across the skin.     

Scanning electrochemical microscopy of iontophoretic transport in hairless mouse skin. Analysis of the relative contributions of diffusion, migration, and electroosmosis to transport in hair follicles

Scanning electrochemical microscopy (SECM) is used to measure spatially localized diffusive and iontophoretic transport rates in hairless mouse skin. Molecular fluxes within individual hair follicles are quantified by measuring the rate at which redox-active probe molecules emerge from the follicle. The influence of an applied current on the flux of an anion (ascorbate), a cation (ferrocenylmethyltrimethylammonium), and a neutral molecule (acetaminophen) is used to determine the contributions of diffusion, migration, and electroosmosis to iontophoretic transport. The direction of electroosmotic transport is consistent with hair follicles possessing a net negative charge at neutral pH. Electroosmosis results in a modest increase in the transport rate of the neutral molecule (a factor of approximately 2.4x at an iontophoretic current density of 0.1 mA/cm(2)). Larger enhancements in the flux of the electrically charged species are associated with migration. The electroosmotic flow velocity within hair follicles is established to be 0.5 (+/-0.1) microm/s at 0.1 mA/cm(2), independent of the electrical charge of permeant. The net volume flow rate across skin resulting from electroosmosis in hair follicles is estimated to be 0.3 microL/cm(2)h. The results suggest that hair follicles are a significant pathway for electroosmotic solution flow during iontophoresis. The radius of the hair follicle openings in hairless mouse skin is measured to be 21 +/- 5 microm.     

Effect of passive and iontophoretic skin pretreatments with terpenes on the in vitro skin transport of piroxicam

The enhancing effect of several terpenes (thymol, menthone and 1,8-cineole) in the percutaneous permeation of piroxicam (Px), either passive or iontophoretically, was investigated. These terpenes were applied, on the skin membrane, as a passive and iontophoretic skin pretreatment. Px was delivered from carbopol gels containing hydroxypropyl-beta-cyclodextrin (2% w/w Px). An increase in Px flux values, both passive and iontophoretic after skin pretreatment with 5% terpenes/50% EtOH, was found to be in the following order: thymol>menthone>1,8-cineole. Iontophoretic skin pretreatment with terpenes produced a slight increase in the passive flux of Px, in comparison with the passive skin pretreatment. This result indicated that iontophoresis could modify the skin morphology and consequently, increase the passive transport of Px. However, when Px was transported iontophoretically, passive skin pretreatment with terpenes, produced higher flux values than iontophoretic skin pretreatment. These results could be explained by the fact that with the iontophoretic pretreatment, terpenes could penetrate into the skin and limitate the movement of the ionized species, across the skin, during the iontophoretic experiments. The amount of Px retained in the skin after all experiments was related to flux values across skin.     

Effect of amino acid sequence on transdermal iontophoretic peptide delivery

The objective of this study was to investigate the effect of amino acid sequence on the transdermal delivery of peptides by iontophoresis. Structurally related, cationic tripeptides based on the residues at positions (i) 6–8 in LHRH (Ac-X-Leu-Arg-NH₂) and (ii) 3–5 in octreotide (Ac-X-dTrp-Lys-NH₂) were studied. Iontophoretic transport experiments were conducted using porcine skin in vitro to investigate the dependence of flux on peptide concentration. Co-iontophoresis of acetaminophen enabled deconvolution of the contributions of electromigration (EM) and electroosmosis (EO) and the calculation of an electroosmotic inhibition factor (IF). A two-fold increase in donor peptide concentration increased iontophoretic flux for most peptides, and electroosmotic inhibition for dNal-containing tripeptides. The improvement in transport and the impact on the EM and EO components were peptide-specific. A reduction in the number of competing ions in the formulation significantly increased transport and, specifically, the EM contribution; it also increased IF of compounds with a propensity to interact with the membrane. No monotonic dependence of flux on either molecular weight or lipophilicity was observed. Iontophoretic peptide transport could not be rationalized in terms of either peptide molecular weight or computational 2D estimates of lipophilicity. Data suggest that a more complex three-dimensional approach is required to develop structure permeation relationships governing iontophoretic peptide delivery.     

Characterization of the permselective properties of rabbit skin during transdermal iontophoresis

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.     

Production of insulin-loaded poly(ethylene glycol)/poly(l-lactide) (PEG/PLA) nanoparticles by gas antisolvent techniques.

Insulin and insulin/poly(ethylene glycol) (PEG)-loaded poly(l-lactide) (PLA) nanoparticles were produced by gas antisolvent (GAS) CO(2) precipitation starting from homogeneous polymer/protein organic solvent solutions. Different amounts of PEG 6000 (0, 10, 30, 50, 100, and 200% PEG/PLA w/w) or concentration of 30% PEG/PLA with PEGs with different molecular weight (MW; 350, 750, 1900, 6000, 10,000, and 20,000) were used in the preparations. The process resulted in high product yield, extensive organic solvent elimination, and maintenance of > 80% of the insulin hypoglycemic activity. Nanospheres with smooth surface and compact internal structure were observed by scanning electron microscopy. The nanospheres presented a mean particle diameter in the range 400-600 nm and narrow distribution profiles. More than 90% of drug and PEG were trapped in the PLA nanoparticles when low MW PEGs were used in the formulation, whereas the addition of high MW PEGs significantly reduced the loading yield. In all cases, in vitro release studies showed that only a little amount of drug was released from the preparations. However, formulations containing low MW PEGs allowed for a slow but constant drug release throughout 1500 h, whereas a burst was obtained by increasing the PEG MW. In conclusion, the GAS process offers a mean to produce protein-loaded nanoparticles possessing the prerequisites for pharmaceutical applications. The PEG added to the formulation was found to play a key role in the simultaneous solute precipitation phenomena and in determining the release behavior and the chemical-physical properties of the formulation.     

Capillary zone electrophoresis for the estimation of transdermal iontophoretic mobility

The objective of the study was to investigate the relationship between transdermal iontophoretic flux--specifically, the electromigratory component--and electrophoretic mobility as determined by capillary zone electrophoresis (CZE). First, the steady-state iontophoretic transport rates of a series of dipeptides across porcine skin were determined in vitro. Co-iontophoresis of acetaminophen was used to quantify the respective contributions of electroosmosis (EO) and electromigration (EM). Second, the electrophoretic mobilities of the dipeptides and three other cationic drugs (lidocaine, propranolol, and quinine) were determined, under equivalent experimental conditions, using CZE. Analysis of the transport data using the results of the CZE experiments revealed a linear dependence (r2 > 0.9) between EM flux and electrophoretic mobility. The CZE measurements also provided insight into the charge state of "zwitterionic" dipeptides, H-Glu-epsilon-Lys-OH and H-Tyr-Gln-OH, revealing that these molecules had partial net negative charges under the formulation conditions, accounting for the absence of anodal iontophoretic delivery. The results suggest that CZE might (i) enable identification of ionization states of complex molecules, (ii) serve as a preliminary screen to identify electrically mobile compounds suitable for iontophoretic delivery, and (iii) prove useful for predicting the EM contribution to transdermal iontophoretic flux.     

Epidermal Iontophoresis: I. Development of the Ionic Mobility-Pore Model

Purpose. An integrated ionic mobility-pore model for epidermal iontophoresis is developed from theoretical considerations using both the free volume and pore restriction forms of the model for a range of solute radii (r _j ) approaching the pore radii (r _p ) as well as approximation of the pore restriction form for r _j /r _p < 0.4. In this model, we defined the determinants for iontophoresis as solute size (defined by MV, MW or radius), solute mobility, solute shape, solute charge, the Debye layer thickness, total current applied, solute concentration, fraction ionized, presence of extraneous ions (defined by solvent conductivity), epidermal permselectivity, partitioning rates to account for interaction of unionized and ionized lipophilic solutes with the wall of the pore and electroosmosis. Methods. The ionic mobility-pore model was developed from theoretical considerations to include each of the determinants of iontophoretic transport. The model was then used to reexamine iontophoretic flux conductivity and iontophoretic flux-fraction ionized literature data on the determinants of iontophoretic flux. Results. The ionic mobility-pore model was found to be consistent with existing experimental data and determinants defining iontophoretic transport. However, the predicted effects of solute size on iontophoresis are more consistent with the pore-restriction than free volume form of the model. A reanalysis of iontophoretic flux-conductivity data confirmed the model's prediction that, in the absence of significant electroosmosis, the reciprocal of flux is linearly related to either donor or receptor solution conductivity. Significant interaction with the pore walls, as described by the model, accounted for the reported pH dependence of the iontophoretic transport for a range of ionizable solutes. Conclusions. The ionic mobility-pore iontophoretic model developed enables a range of determinants of iontophoresis to be described in a single unifying equation which recognises a range of determinants of iontophoretic flux.     

Impact of molecular weight on the mechanism of cellular uptake of polyethylene glycols (PEGs) with particular reference to P-glycoprotein

Polyethylene glycols (PEGs) in general use are polydisperse molecules with molecular weight (MW) distributed around an average value applied in their designation e.g., PEG 4000. Previous research has shown that PEGs can act as P-glycoprotein (P-gp) inhibitors with the potential to affect the absorption and efflux of concomitantly administered drugs. However, questions related to the mechanism of cellular uptake of PEGs and the exact role played by P-gp has not been addressed. In this study, we examined the mechanism of uptake of PEGs by MDCK-mock cells, in particular, the effect of MW and interaction with P-gp by MDCK-hMDR1 and A549 cells. The results show that: (a) the uptake of PEGs by MDCK-hMDR1 cells is enhanced by P-gp inhibitors; (b) PEGs stimulate P-gp ATPase activity but to a much lesser extent than verapamil; and (c) uptake of PEGs of low MW (<2000 Da) occurs by passive diffusion whereas uptake of PEGs of high MW (>5000 Da) occurs by a combination of passive diffusion and caveolae-mediated endocytosis. These findings suggest that PEGs can engage in P-gp-based drug interactions which we believe should be taken into account when using PEGs as excipients and in PEGylated drugs and drug delivery systems.     

In vitro iontophoretic delivery of nicorandil

The present investigation is aimed at assessing the iontophoretic permeability of nicorandil to evaluate its feasibility for the development of an actively delivered transdermal system. Excised porcine skin was used for permeation study, and steady state flux was optimized with respect to donor concentration, current density, and voltage. Constant current iontophoresis was carried out at 0.3, 0.5, and 0.7 mA/cm(2), whereas constant voltage studies were carried out at 3, 5, and 6.5 V. The effect of donor drug concentration (11.8, 55.8, and 104.8 mg/mL) was studied at the optimized condition of 5 V. An apparent increase in steady state flux was observed in constant current studies, but the increment over the passive diffusion was statistically insignificant (P > 0.05). In contrast, steady state flux was found to be higher than that of passive fluxes when permeation was carried out at 5 and 6.5 V (P < 0.001). Incorporation of alcohol in the donor vehicle increased solubility, but there was a tradeoff in terms of lag time. Conformity with the Nernst-Planck convective transport model suggested that electroosmosis was the dominant mechanism of permeation.     

Safety assessment on polyethylene glycols (PEGs) and their derivatives as used in cosmetic products

This assessment focusses on polyethylene glycols (PEGs) and on anionic or nonionic PEG derivatives, which are currently used in cosmetics in Europe. These compounds are used in a great variety of cosmetic applications because of their solubility and viscosity properties, and because of their low toxicity. The PEGs, their ethers, and their fatty acid esters produce little or no ocular or dermal irritation and have extremely low acute and chronic toxicities. They do not readily penetrate intact skin, and in view of the wide use of preparations containing PEG and PEG derivatives, only few case reports on sensitisation reactions have been published, mainly involving patients with exposure to PEGs in medicines or following exposure to injured or chronically inflamed skin. On healthy skin, the sensitising potential of these compounds appears to be negligible. For some representative substances of this class, information was available on reproductive and developmental toxicity, on genotoxicty and carcinogenic properties. Taking into consideration all available information from related compounds, as well as the mode and mechanism of action, no safety concern with regard to these endpoints could be identified. Based on the available data it is therefore concluded that PEGs of a wide molecular weight range (200 to over 10,000), their ethers (laureths. ceteths, ceteareths, steareths, and oleths), and fatty acid esters (laurates, dilaurates, stearates, distearates) are safe for use in cosmetics. Limited data were available for PEG sorbitan/sorbitol fatty acid esters, PEG sorbitan beeswax and PEG soy sterols. Taking into account all the information available for closely related compounds, it can be assumed that these compounds as presently used in cosmetic preparations will not present a risk for human health. PEG castor oils and PEG hydrogenated castor oils have caused anaphylactic reactions when used in intravenous medicinal products. Their topical use in cosmetics is, however, considered safe as they are not expected to be systemically available. As all PEGs and PEG derivatives, they must not be applied to damaged skin. Manufacturers of PEGs and PEG derivatives must continue their efforts to remove impurities and by-products such as ethylene oxide and 1,4-dioxane. Overall, it is concluded, that the PEGs covered in this review are safe for use in cosmetics under the present conditions of intended use.     

Factors affecting iontophoretic mobility of metoprolol.

The effect of different factors on the iontophoretic transport of metoprolol was analyzed. In vitro experiments were first performed in a diffusion cell with a cellophane membrane. Comparison of different pH, buffers, and ionic strengths in the donor compartment showed that higher iontophoretic transport was obtained with phthalate buffer (0.01 M) at pH 3. When the current density increased, the flux of metoprolol also increased. A decrease in drug concentration or an increase in viscosity slowed down the iontophoretic transport of metoprolol. The fluxes of metoprolol through hairless rat skin were strongly enhanced compared with passive diffusion. Direct current seemed to be more efficient than pulse current. When the on:off ratio of the pulse current was reduced, the flux also decreased.     

Measurement of ileal permeability with different-sized polyethylene glycols (PEG 400, 600, and 1000)

Polyethylene glycols (PEGs; 400, 600, and 1000) were used to study the molecular weight (MW) permeability dependence in the rat ileal mucosa. Absorption of the PEGs was measured by following their recirculation perfusion over a 3 hr collection period. HPLC methods were used to separate and quantitate the individual oligomers present in the solution of PEGs mixtures (MW range 330 to 1122 D). In the range studied, a distinct molecular weight cutoff was not identified. Corrected for the length of ileum used in the study, over the molecular weight range 330 to 1122 D, the apparent permeability (P_app) of PEG ranged from 3.2±0.06×10^?5 cm/sec (mean±SEM, n=7) to 0.1±0.02×10^?5 cm/sec. Also, it was observed that the apparent permeability was inversely proportional to approximately MW^2.4.     

Effect of Charge and Molecular Weight on Transdermal Peptide Delivery by Iontophoresis

Purpose The study was conducted to investigate the impact of charge and molecular weight (MW) on the iontophoretic delivery of a series of dipeptides. Methods Constant current iontophoresis of lysine and 10 variously charged lysine- and tyrosine-containing dipeptides was performed in vitro. Results Increasing MW was compensated by additional charge; for example, Lys (MW = 147 Da, +1) and H-Lys-Lys-OH (MW = 275 Da, +2) had equivalent steady-state fluxes of 225 ± 48 and 218 ± 40 nmol cm⁻² h⁻¹, respectively. For peptides with similar MW, e.g., H-Tyr-d-Arg-OH (MW = 337 Da, +1) and H-Tyr-d-Arg-NH₂ (MW = 336 Da, +2), the higher valence ion displayed greater flux (150 ± 26 vs. 237 ± 35 nmol cm⁻² h⁻¹). Hydrolysis of dipeptides with unblocked N-terminal residues, after passage through the stratum corneum, suggested the involvement of aminopeptidases. The iontophoretic flux of zwitterionic dipeptides was less than that of acetaminophen and dependent on pH. Conclusions For the series of dipeptides studied, flux is linearly correlated to the charge/MW ratio. Data for zwitterionic peptides indicate that they do not behave as neutral (“charge-less”) molecules, but that their iontophoretic transport is dependent on the relative extents of ionization of the constituent ionizable groups, which may also be affected by neighboring amino acids.     

Modulating pharmacokinetics of an anti-interleukin-8 F(ab')(2) by amine-specific PEGylation with preserved bioactivity

By covalently attaching biocompatible polyethylene-glycol (PEG) groups to epsilon-amino groups of the F(ab')(2) form of a humanized anti-interleukin-8 (anti-IL-8) antibody, we sought to decrease the in vivo clearance rate to give a potentially more clinically acceptable therapeutic. The in vivo clearance was modulated by changing the hydrodynamic size of the PEGylated antibody fragments. To achieve significant increases in the hydrodynamic size with minimal loss in bioactivity, high molecular weight linear or branched PEG molecules were used. Modification involved N-hydroxy-succinamide reaction of the PEGs with primary amines (lysines and/or the N-terminus) of the anti-IL-8 F(ab')(2). The process of adding up to four linear 20 kDa PEG, or up to two branched 40 kDa PEG, gave reproducible distribution of products. The components with uniform size (as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) were purified by a single-step ion-exchange high-performance liquid chromatography and showed no significant loss of biological activity in ligand binding and cell-based assays. Addition of a single branched 40 kDa PEG to a F(ab')(2) (molecular weight (MW)=1.6 million Da) or up to two 40 kDa branched PEG (MW=1.9 million Da) increased the serum half-life to 48 h as compared with the unPEGylated F(ab')(2) with a half-life of 8.5 h. This study shows that by attaching high molecular weight PEGs at a one or two sites, bioactive antibody fragments can be made reproducibly with sizes tailored to achieve the desired pharmacokinetics.     

Transdermal iontophoretic delivery of selegiline hydrochloride,in vitro

Transdermal iontophoretic delivery of selegiline hydrochloride (SH) across dermatomed human skin was studied. Electrochemical stability and various factors affecting the skin permeation were investigated. SH was stable under the influence of an electrical field. The permeation of SH was very low by passive delivery (2.29?±?0.05 μg/cm²/h) as compared to iontophoresis at 0.5 mA/cm² (65.10?±?5.04 μg/cm²/h). An increase in drug concentration from 1 to 20?mg/mL increased the iontophoretic flux by 13-fold. Optimal pH and salt (NaCl) concentration for iontophoretic delivery of SH were found to be pH 5 and 100?mM, respectively. Overall, with 20?mg/mL SH and a current density of 0.4 mA/cm², a maximum flux of 305.5?μg/cm²/h was obtained. Based on reported pharmacokinetic parameters, input target delivery rate to achieve effective plasma concentration of SH (2.2?ng/mL) was calculated. With a surface area of 40?cm², iontophoretic delivery can provide six to seven times higher levels of SH than the target delivery rate, which enables lowering of the dose and/or patch surface area. Further in vivo studies will be required to prove the efficacy of ionophoresis for enhanced delivery of SH.     

Iontophoretic Delivery of Apomorphine In Vitro: Physicochemic Considerations

Purpose. To examine the mechanisms of transdermal iontophoretic delivery of apomorphine. Methods. Anodal iontophoresis of R-apomorphine across human stratum corneum was determined in vitro. The effects on the flux of the following parameters were studied: stability of drug, pH of donor solution, concentration of NaCl, and type of Na⁺ co-ions. Results. Ascorbic acid was effective to prevent apomorphine degradation. The iontophoretic transport of apomorphine was strongly influenced by the pH of the donor formulation. Increasing the pH from 3 to 6 resulted in an increase in the iontophoretic apomorphine flux from 27.9 ± 4.4 nmol/cm²*h to 78.2 ± 6.9 nmol/cm²*h. Upon decreasing NaCl concentration from 8 to 2 g/L, the iontophoretic flux was not significantly changed. Replacing NaCl in the donor formulation by tetraethylammonium chloride or tetrabutylammonium chloride resulted in 1.3 fold greater steady-state flux. Conclusions. For optimized apomorphine iontophoretic delivery, a constant pH of the donor formulation is of great importance. The results suggest that although flux enhancement during iontophoresis is largely due to the electrical potential gradient, secondary effects, such as convective flow and electroosmosis may also contribute.