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  • 1
    Electronic Resource
    Electronic Resource
    Estradiol Permeation from Nonionic Surfactant Vesicles Through Human Stratum Corneum in Vitro (1994)
    Springer
    Pharmaceutical research 11 (1994), S. 659-664 
    Details
    ISSN: 1573-904X
    Keywords: niosomes ; nonionic surfactant vesicles ; estradiol ; transdermal delivery ; stratum corneum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The permeation of estradiol from vesicular formulations through human stratum corneum was studied in vitro. The vesicles were composed of nonionic n-alkyl polyoxyethylene ether surfactants (CnEOm). The thermodynamic activity of estradiol present in each formulation was kept constant by saturating all formulations with estradiol. The effects of both the particle size and the composition of the formulation on estradiol permeation across excised human stratum corneum were investigated. Stratum corneum that was pre-treated with empty surfactant carriers allowed for significantly higher estradiol fluxes compared with untreated stratum corneum. However, estradiol fluxes obtained in these pretreatment experiments appeared to be significantly lower than those obtained by the direct application of the estradiol-saturated carrier formulation on top of the stratum corneum. Furthermore, in the case of pretreatment of the stratum corneum, an increase in carrier size resulted in a decrease in estradiol flux. For direct application the opposite was found. Two mechanisms are proposed to play an important role in vesicle–skin interactions, i.e., the penetration enhancing effect of surfactant molecules and the effect of the vesicular structures that are most likely caused by adsorption of the vesicles at the stratum corneum–suspension interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018963910260
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  • 2
    Electronic Resource
    Electronic Resource
    lontophoretic Delivery of Apomorphine I: In Vitro Optimization and Validation (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 1798-1803 
    Details
    ISSN: 1573-904X
    Keywords: iontophoresis ; apomorphine ; in vitro/in vivo correlation ; human skin ; skin metabolism ; Parkinson's disease
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To investigate the feasibility of transdermal iontophoretic delivery of apomorphine in patients with Parkinson's disease, transdermal transport rates were optimized and validated across human stratum corneum and freshly dermatomed human skin in vitro. Methods. In all experiments R-apomorphine hydrochloride was applied in the anodal compartment. The effect on the flux of the following parameters was studied, using a flow through transport cell: current density, pH, concentration, ionic strength, osmolarity, buffer strength, temperature and skin type. Results. Transdermal transport of apomorphine was directly controlled by the presence or absence of current. Passive delivery was minimal and no depot effect was observed. A linear relationship was found between current density and steady-state flux. At room temperature the lag time was 30 to 40 minutes. A maximal steady-state flux was obtained when the donor concentration approached maximum solubility. By increasing the temperature of the acceptor chamber to 37°C, the steady-state flux was increased by a factor of 2.3 and the lag time decreased to ± 3 minutes. No effect of osmolarity and buffer strength, and only a small effect of ionic strength and pH on the transport rate were observed. The flux through dermatomed human skin was decreased compared to stratum corneum. This effect was shown not to be caused by skin metabolism. Conclusions. The results obtained in vitroindicate that the iontophoretic delivery of apomorphine can be controlled and manipulated accurately by the applied current. The in vitro flux furthermore depends on the donor composition, temperature and skin type. Under optimized conditions, transport rates resulting in therapeutically effective plasma concentrations are feasible, assuming a one to one in vitro/in vivo correlation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012100417645
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  • 3
    Electronic Resource
    Electronic Resource
    lontophoretic Delivery of Apomorphine II: An In Vivo Study in Patients with Parkinson's Disease (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 1804-1810 
    Details
    ISSN: 1573-904X
    Keywords: iontophoresis ; Parkinson's disease ; human ; pharmacodynamics ; transdermal delivery ; apomorphine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Transdermal transport rates of the dopamine agonist R-apomorphine were determined in patients with idiopathic Parkinson's disease (IPD). Apomorphine was applied by iontophoresis at two current densities. Methods. In ten patients apomorphine was applied passively for one hour. Thereafter, in the first five patients, a current density of 250 μA.cm−2 was applied for one hour and a current density of 375 μA.cm−2 in the second group. The individual pharmacokinetic parameters were obtained separately following a 15-minute zero-order intravenous infusion of 30 μg.kg−1. Skin resistance was measured during current delivery. Current-induced irritation was measured by Laser Doppler Flowmetry (LDF). The pharmacodynamics were quantified by a unilateral tapping score. Qualitative clinical improvements (decreased tremor, rigidity or cramp) were also recorded. Results. In all patients increasing plasma concentrations of R-apomorphine were found during the interval of current application. The maximum concentrations that were attained were related to the applied current density: 1.3 ± 0.6 ng.ml−1 at 250 μA.cm−2 and 2.5 ± 0.7 ng.ml−1 at 375 μA.cm−2. When the current was switched off all concentrations returned to baseline values in about 90 minutes. By mathematical deconvolution of the profiles it was shown that steady-state fluxes were reached within the one-hour interval of current driven transport. Steady-state fluxes were calculated to be 69 ± 30 nmol.cm−2.h−1 at 250 μA.cm−2 and 114 ± 34 nmol.cm−2.h−1 at 375 μA.cm−2. Individual drug input rates were inversely related to the overall resistance. Significantly elevated LDF values were found after patch removal, indicating mild current induced erythema. Only subtherapeutic plasma concentrations were obtained in all patients except for one. Conclusions. The results show that current-dependent delivery of apomorphine is possible in vivo at acceptable levels of skin irritation. Excellent correlation was found between the calculatedin vivo transport rates and the rates that were previously obtained in vitro.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012152401715
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  • 4
    Electronic Resource
    Electronic Resource
    Iontophoresis of Bases, Nucleosides, and Nucleotides (1996)
    Springer
    Pharmaceutical research 13 (1996), S. 553-558 
    Details
    ISSN: 1573-904X
    Keywords: iontophoresis ; electroosmosis ; transdermal delivery ; skin penetration ; bases ; nucleosides ; nucleotides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To investigate whether transdermal iontophoresis may be potentially useful for delivery of oligonucleotide drugs, the electro-transport of representative bases (uracil and adenine), nucleosides (uridine and adenosine) and nucleotides (AMP, ATP, GTP and imido-GTP) across mammalian skin in vitro has been considered. Methods. While the passive permeability of all compounds investigated (from 1 mM solutions at pH 7.4) was very low, the application of constant current iontophoresis (0.55 mA/cm2) significantly enhanced the transport of both charged and uncharged species. Results. The efficiency of delivery depended only weakly upon lipophilicity, varied quite linearly with concentration (for AMP and ATP), was inversely sensitive to molecular weight, and was strongly influenced by charge. Neutral solutes were delivered better from the anode than the cathode, as expected; post-iontophoresis, passive permeabilities were greater than those of the untreated controls, suggesting that iontophoretically-induced changes in barrier function cannot be completely repaired in in vitro model systems. The triphosphate nucleotides, ATP and GTP, were essentially completely metabolized (presumably to their corresponding mono-phosphates) during their iontophoretic delivery, while imido-GTP was apparently resistant to enzymatic attack; however, comparison of the transport data from AMP and ATP suggested that ATP metabolism occurred primarily after the rate-limiting step of iontophoresis. Conclusions. The results obtained are consistent with the general patterns of behavior previously observed in investigations of amino acid and peptide electrotransport. It remains to be seen whether extension of the research described here to larger oligonucleotide species is a feasible long-term objective.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016041904037
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    Paper (German National Licenses)
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