Iontophoretic delivery of drugs: Fundamentals, developments and biomedical applications

Electromotive administration of a new morphine formulation: morphine citrate

Two formulations of morphine citrate were synthesized: trimorphine citrate, 3(MH)+(C6H5O7)3- and morphine sodium citrate, 3(MH)+3Na+2(C6H5O7)3-. Four healthy individuals volunteered to undergo electromotive administration of the two formulations. Application of electric current (2 mA) to solutions of trimorphine citrate for 1 h resulted in iontophoretic transcutaneous administration of therapeutic quantities of morphine, without deleterious reduction in the pH of the drug solutions. Application of a 2-mA current to solutions of morphine sodium citrate for 2 h resulted in combined iontophoretic and electrophoretic delivery of morphine with increased administration rates and an improved buffering capacity of the drug solutions.

Ultrasonically enhanced transdermal drug delivery. Experimental approaches to elucidate the mechanism

The effect of therapeutic range ultrasound on skin permeability was studied in vitro. Permeating molecule ionization state, pH, ultrasound duration, reversibility of the enhancement phenomenon, and skin structural alterations were evaluated. It was found that ultrasound affects the permeability of both ionized and unionized molecules. No irreversible structural alterations due to the ultrasound exposure were detected in the stratum corneum. Ultrasound enhancing mechanism was discussed.

Model describing transdermal iontophoretic delivery of lidocaine incorporating consideration of cutaneous microvascular state

A three-compartment pharmacokinetic model describing percutaneous absorption of iontophoretically driven topically applied lidocaine in the isolated perfused porcine skin flap is presented. Delivery from the active (drug-dosed) electrode to skin is estimated as a ramp input profile. Model parameters were estimated separately for dosing (4 h current-on) and washout (4 h current-off) periods in experiments with coadministered vasoactive drugs [tolazoline (vasodilator) and norepinephrine (vasoconstrictor)] and controls (lidocaine alone). The model presented was able to predict 8-h lidocaine absorptions and compartmental mass profiles for each of the three treatments, was able to document vascular effects of co-iontophoresed vasoactive compounds, and gives insight into the factors that modulate cutaneous disposition of iontophoretically delivered lidocaine in a biologically relevant model approximating in vivo delivery.

Comparison of depolarizing and direct current systems on iontophoretic enhancement of transport of sodium benzoate through human and hairless rat skin

A direct current (DC) system and a pulsed depolarization (PD) system were evaluated for their iontophoretic permeation of sodium benzoate, as a model drug, through hairless rat and human skin. Approximately the same initial permeation of sodium benzoate through the hairless rat skin was obtained at 0.1 mA for the DC device and at 3.0 mA for the PD device. Study of the drug's permeation was performed using a two-chamber iontophoretic diffusion cell, over two cycles of three successive on-off experimental conditions [stage I (off) 0-4 h, II (on) 4-6 h, III (off) 6-10 h, saline washing 10-24 h, IV (off) 24-28 h, V (on) 28-30 h and VI (off) 30-34 h]. Skin permeation rate during stage IV of the iontophoresis as compared with the control group through hairless rat or human skin for the DC system was 2-4 times that in stage I, whereas in the same stage using the PD system it was almost the same as in stage I. Impedance of skin decreased during the application of either system (stage II); however, the value significantly recovered during stage III only in the case of the PD system use on human skin. Histological observation revealed no tissue alteration in the hairless rat skin after using either system. When the DC or PD system was applied to volunteers, the minimum current density producing pain was 0.016 or 2.7 mA cm-2, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of vasoactive drugs on transdermal lidocaine iontophoresis

The effect of co-administration of vasoactive drugs on the transdermal iontophoretic delivery of lidocaine.HCI was studied in in vitro cells, in the isolated perfused porcine skin flap (IPPSF), and in vivo in pigs. Iontophoresis of lidocaine in vitro across human and porcine skin were similar, supporting the use of porcine skin as an appropriate animal model. Co-iontophoresis of the vasodilator tolazoline marginally decreased lidocaine flux in vitro, but significantly increased it in the IPPSF and in vivo. In contrast, norepinephrine decreased lidocaine flux in the IPPSF. Vasomodulation also changed the shape of the venous efflux profile in the IPPSF as evidenced by changes in fractional absorption index, as well as the AUC. These studies demonstrate that co-iontophoresis of vasoactive compounds may significantly alter the transdermal delivery of lidocaine and that use of vitro animal model systems which possess a functional microcirculation are essential to study this process if reliable extrapolation to the in vivo setting is desired.

Development, characterization and evaluation of an auto-regulatory delivery system for insulin

A self-regulatory delivery system for insulin was designed, based on the competitive and complementary binding behaviour of Concanavalin with glucose and glycosylated insulin. By encapsulating the Con-A bound G- insulin in a suitable polymer membrane, which was permeable to both glucose and insulin, the insulin efflux was regulated in response to glucose influx.

Percutaneous delivery of proteins and peptides using iontophoretic techniques

There has been much interest recently in the delivery of proteins and peptides following the research and development of biotechnology: derived drugs and other bioactive substances. This article summarizes the use of iontophoresis to deliver proteins and peptides across the skin. This technique offers considerable promise for delivering drugs in therapeutic amounts by bypassing the gastrointestinal tract (GIT) and liver metabolism. This article discusses the theory underlying iontophoretic drug delivery and the devices available. The future development of these systems would require the use of specialized approaches to enhance delivery of larger molecules but overall there is considerable optimism.

Enhancement of propranolol hydrochloride and diazepam skin absorption in vitro: effect of enhancer lipophilicity

The enhancement of model hydrophilic (propranolol hydrochloride) and lipophilic (diazepam) drug penetration across rat and hairless mouse skin in vitro has been studied. Preliminary experiments established that most n-alkanes having chain lengths of between 7 and 16 promote the flux of both drugs. For propranolol, enhancement varied parabolically with carbon number; for diazepam, heptane was ineffective and all others were essentially equipotent. Enhancement by n-nonane was then compared with that by n-nonanol. Propranolol flux was increased by both enhancers, whereas diazepam penetration was not affected by the less lipophilic alcohol. The enhancement of propranolol by n-nonane and n-nonanol was examined as a function of adjuvant concentration in the applied formulation. Maximum increases in maximum penetration rates of 6.5-fold (n-nonane) and 8.2-fold (n-nonanol) were determined. As expected, the enhancement was saturable, indicative of a maximally perturbed stratum corneum. Finally, the penetration enhancing abilities of six monoterpenes were assessed. The purely hydrocarbon analogues promoted both propranolol and diazepam transport to an extent similar to that of n-nonane. The terpenes with hydrogen-bonding ability, however, only enhanced propranolol flux (at a level comparable to n-nonanol). While the data reported do not directly reveal mechanistic information on percutaneous penetration enhancement, they do provide a starting point for the rational investigation of interrelationships between drug, enhancer, and skin. Such information is clearly essential for the optimization and exploitation of transdermal drug delivery.

Iontophoresis of polypeptides: effect of ethanol pretreatment of human skin

This paper explores the possibility of iontophoretically enhancing the in vitro transdermal flux of two polypeptides: leuprolide (a LHRH analogue; MW = 1209.4) and a cholecystokinin-8 analogue (CCK-8; MW = 1150.17). Control experiments at an applied voltage of 0.5 V across full-thickness human skin did not yield measurable fluxes of either polypeptide, suggesting that despite the expected iontophoretic flux enhancements, the intrinsic permeability of these polypeptides through skin may be too low to allow significant amounts of the drug to permeate. Therefore, pretreatment with ethanol (to simulate the effect of a chemical permeation enhancer) followed by iontophoresis was investigated with the aim of evaluating the potential of the enhancer plus ionophoresis as a means for controlled transdermal delivery of these polypeptides. The ethanol pretreatment dramatically increased the passive fluxes of both polypeptides, and iontophoresis produced further enhancements in their fluxes. Also, the experimental enhancement factors for leuprolide as a function of the applied voltage appeared to be generally lower than the predictions of the constant field theory. A synergism of iontophoresis with a chemical permeation enhancer may be a potential route for controlled transdermal delivery of these and other high molecular weight polypeptides.

Transdermal iontophoretic drug delivery: mechanistic analysis and application to polypeptide delivery

Three factors are of primary importance in determining the iontophoretic flux of a charged solute: the electrochemical potential gradient across the skin, an increase in skin permeability to passive transport due to iontophoresis (loosely defined as skin damage), and a current-induced water flux. The latter two factors can also affect the transport of uncharged solutes during iontophoresis. A method of correcting for the skin damage effect is introduced. The contributions of the water transport effect relative to that of the applied voltage drop for charged solutes is estimated. It is shown that the water transport contribution is generally lower than the contribution due to the applied voltage drop. The observed iontophonetic flux of the enhancement factors due to the applied voltage drop alone are compared with the theoretical predictions based on the constant field assumption. It is shown that the theoretical predictions are higher than the experimental observations. This work also examines, for the first time, a synergism of iontophoresis and pretreatment with a chemical penetration enhancer as a means for delivering high molecular weight polypeptides. It is shown that a 2-h pretreatment with absolute ethanol followed by iontophoresis dramatically increases the permeability coefficient of insulin through human skin.

Iontophoretic delivery of model inorganic and drug ions

The in vitro delivery of the inorganic ions Li+, Na+, K+, Mg2+, and Ca2+, and the model organic ions pyridostigmine and propranolol through various types of excised skin was investigated using a constant current iontophoretic system. The drug delivery rate was found to be linearly dependent on current for each ion. The slope of this linear dependence is defined as the iontophoretic flux and was used to calculate the efficiency of drug delivery which was found to be virtually independent of the type of skin employed. However, the efficiency of drug delivery was affected by the anode material and drug counterion employed in the iontophoretic system. In addition, the efficiency of delivery for divalent magnesium and calcium ions was found to be less than half that observed for the monovalent sodium and potassium ions. The in vivo iontophoretic delivery of pyridostigmine using the domestic weanling pig is also reported. The in vivo results were found to be similar to those observed in vitro.