Effect of formulation factors on electroosmotic glucose transport through human skin in vivo

Simultaneous Transdermal Delivery of Buprenorphine Hydrochloride and Naltrexone Hydrochloride by Iontophoresis

The opioids buprenorphine hydrochloride (BUP) and naltrexone hydrochloride (NTX) show promise as a combination treatment for addiction, but no means of delivering the two compounds in one medicine currently exist. In this paper, we report sufficient input rates of both these drugs from one iontophoretic transdermal drug delivery system. Experiments were performed using dermatomed pig skin mounted in glass side-bi-side cells. BUP and NTX were iontophoretically delivered together from the anode using direct constant current from Ag/AgCl electrodes. The transdermal drug fluxes and the masses of drugs in both the stratum corneum and the underlying epidermis/dermis were measured. The apparent electroosmotic flow was quantified using a neutral marker (acetaminophen). The effects of donor composition (drug concentration/molar fraction and pH), current density and profile, and the choice of receptor solution were assessed. Iontophoresis dramatically increased the flux of both drugs compared to passive control values. Target fluxes (calculated from literature clearance values and required therapeutic plasma concentrations) were greatly exceeded for NTX and were met for BUP. The latter accumulated in the skin and suppressed electroosmotic flow, inhibiting both its own flux and that of NTX. NTX, in turn, negatively influenced the flux of BUP via co-ion competition. Lowering current density by increasing the delivery area resulted in increased electroosmotic flow but did not significantly affect current-normalized drug fluxes. Delivering the drugs from both electrodes and reversing the polarity for every 2 h did not increase the flux of either compound. In summary, during iontophoresis, BUP and NTX inhibited each other's flux by two distinct mechanisms. While the more complex behavior of BUP complicates the optimization of this drug combination, iontophoresis nevertheless appears to be a feasible approach for the controlled codelivery of NTX and BUP through the skin.

Iontophoresis-targeted, follicular delivery of minoxidil sulfate for the treatment of alopecia

Although minoxidil (MX) is a drug known to stimulate hair growth, the treatment of androgenic alopecia could be improved by delivery strategies that would favor drug accumulation into the hair follicles. This work investigated in vitro the potential of iontophoresis to achieve this objective using MX sulfate (MXS), a more water-soluble derivative of MX. Passive delivery of MXS was first determined from an ethanol-water solution and from a thermosensitive gel. The latter formulation resulted in greater accumulation of MXS in the stratum corneum (skin's outermost layer) and hair follicles and an overall decrease in absorption through the skin. Anodal iontophoresis of MXS from the same gel formulation was then investigated at pH 3.5 and pH 5.5. Compared with passive delivery, iontophoresis increased the amount of drug reaching the follicular infundibula from 120 to 600 ng per follicle. In addition, drug recovery from follicular casts was threefold higher following iontophoresis at pH 5.5 compared with that at pH 3.5. Preliminary in vivo experiments in rats confirmed that iontophoretic delivery of MXS facilitated drug accumulation in hair follicles. Overall, therefore, iontophoresis successfully and significantly enhanced follicular delivery of MX suggesting a useful opportunity for the improved treatment of alopecia.

Amikacin reverse iontophoresis: optimization of in vitro extraction

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.

Alternating current (AC) iontophoretic transport across human epidermal membrane: effects of AC frequency and amplitude

PURPOSE

As a continuing effort to understand the mechanisms of alternating current (AC) transdermal iontophoresis and the iontophoretic transport pathways in the stratum corneum (SC), the objectives of the present study were to determine the interplay of AC frequency, AC voltage, and iontophoretic transport of ionic and neutral permeants across human epidermal membrane (HEM) and use AC as a means to characterize the transport pathways.

MATERIALS AND METHODS

Constant AC voltage iontophoresis experiments were conducted with HEM in 0.10 M tetraethyl ammonium pivalate (TEAP). AC frequencies ranging from 0.0001 to 25 Hz and AC applied voltages of 0.5 and 2.5 V were investigated. Tetraethyl ammonium (TEA) and arabinose (ARA) were the ionic and neutral model permeants, respectively. In data analysis, the logarithm of the permeability coefficients of HEM for the model permeants was plotted against the logarithm of the HEM electrical resistance for each AC condition.

RESULTS

As expected, linear correlations between the logarithms of permeability coefficients and the logarithms of resistances of HEM were observed, and the permeability data were first normalized and then compared at the same HEM electrical resistance using these correlations. Transport enhancement of the ionic permeant was significantly larger than that of the neutral permeant during AC iontophoresis. The fluxes of the ionic permeant during AC iontophoresis of 2.5 V in the frequency range from 5 to 1,000 Hz were relatively constant and were approximately 4 times over those of passive transport. When the AC frequency decreased from 5 to 0.001 Hz at 2.5 V, flux enhancement increased to around 50 times over passive transport.

CONCLUSION

While the AC frequency for achieving the full effect of iontophoretic enhancement at low AC frequency was lower than anticipated, the frequency for approaching passive diffusion transport at high frequency was higher than expected from the HEM morphology. These observations are consistent with a transport model of multiple barriers in series and the previous hypothesis that the iontophoresis pathways across HEM under AC behave like a series of reservoirs interconnected by short pore pathways.