Grazia Stagni

Intradermal microdialysis: kinetics of iontophoretically delivered propranolol in forearm dermis.

Intradermal microdialysis permits us to measure the concentration in dermis of drugs applied to the skin. Microdialysis is especially efficient in sampling water-soluble molecules. Consequently, it appears particularly suitable to study current based delivery systems like iontophoresis that deliver ions or highly polar molecules. The purpose of this work was to evaluate the adequacy of a skin microdialysis technique to characterize and quantify the dermatopharmacokinetics of iontophoretically delivered propranolol in the dermis of healthy human volunteers. Linear microdialysis probes were inserted in the subjects forearm skin and an iontophoresis device was installed above them. Constant current was applied for two periods of 1 h each separated by a 1-h interval. Dialysate samples were collected every 6 min for 4.4 h and analyzed by HPLC. Probes were always placed in the dermis as measured by ultrasonography. Propranolol was detectable in the dialysate. It was possible to build detailed concentration vs. midtime profiles that mirrored the current applied. Elimination rate from the dermis had first-order kinetics and was similar in all subjects. Quantification of the absorption process, indexed by lag-time and area under the concentration curve showed a high inter- and intrasubject variability that did not correlate with probe depth.

Pharmacokinetics of Antimony in Children Treated for Leishmaniasis with Meglumine Antimoniate

BACKGROUND In some settings, the response to pentavalent antimonial therapy for leishmaniasis may be lower in children than in adults. We hypothesized that there are age-dependent pharmacokinetic differences of potential clinical relevance. METHODS We compared the pharmacokinetics of antimony (Sb) in adults and 2 groups of children 3-6 years old who had cutaneous leishmaniasis treated with intramuscular meglumine antimoniate. Adults (n=9) and the first group of children (n=9) received 20 mg Sb/kg/day for 20 days; the second group of children (n=6) received 20 mg Sb/kg for 19 days and 30 mg Sb/kg on day 20. Drug exposure was assessed by the area under the 24-h time-concentration curve (AUC(0-24)) in plasma. RESULTS Children (vs. adults) who received 20 mg/kg had a 42% lower AUC(0-24) (mean +/- SE, 111+/-7 vs. 190+/-10 mg x h/L, compared with adults; P<.001), a 16% lower peak concentration (32.7+/-0.9 vs. 38.8+/-2.1 mg/L; P=.04), and a 75% higher weight-adjusted clearance (0.185+/-0.013 vs. 0.106+/-0.006 L/h/kg; P<.001). The 30 mg/kg dose in children increased the AUC(0-24) to 164+/-10 mg x h/L and the peak concentration to 43.8+/-2.3 mg/L. CONCLUSIONS Drug exposure is significantly lower in children than in adults treated with the same weight-adjusted regimen of meglumine antimoniate, which primarily stems from a higher antimony clearance rate.

Iontophoretic current and intradermal microdialysis recovery in humans

When microdialysis (MD) is used to study dermal delivery by iontophoresis, the effects of current may alter MD recovery through an increase in temperature, a change of pH, hyperemia, and dermal hydration. The objective of this work is to assess whether these effects of current may cause a measurable change in the retrodialysis of a model compound (sodium fluorescein, Fl). Two linear MD-probes were inserted in the forearm dermis of healthy human volunteers and perfused with Ringers solution containing Fl. Two identical iontophoresis chambers (IC, filled with NaCl in propylene glycol) were placed over the MD-probes. Each IC included a laser Doppler flowmetry probe to monitor skin blood flow. At one IC, current was applied for two periods of 30 min each, separated by 30 min of no current. No current was applied to the control site. Dialysate samples were collected every 5 min and analyzed for Fl by HPLC. Skin blood flow increased in response to iontophoresis, on average, 570% compared to the control site. However, there was no difference in the recovery of Fl between the current-active site versus the control site, and between the period with applied current versus the period with no current. In conclusion, iontophoretic current did not affect intradermal MD recovery.

In vivo Quantification of Acyclovir Exposure in the Dermis Following Iontophoresis of Semisolid Formulations

The objective was to quantify acyclovir (ACV) exposure in the dermis following iontophoresis of nontraditional (pH-11 gels) and traditional (neutral cream) topical formulations of ACV. Given that the application time of a formulation on the skin can be significantly reduced with iontophoresis, the use of formulations optimized for iontophoretic delivery was explored to maximize the delivery of ACV to the site of action for the treatment of Herpes-labialis. Microdialysis probes were inserted into the shaved skin of tranquilized rabbits. Iontophoresis was performed at a constant current density of 200 microA/cm(2) for 60 min using a single-use drug cartridge filled with the following formulations: neutral cream, soluble fraction of the same cream (anodal and cathodal-current), or two formulations of pH-11 gels, one without and one with stabilizers and preservatives (cathodal-current). Results showed that only the ACV in the water phase of the cream is available for transport. All of the pH-11 gels exhibited a statistically significant (p < 0.001) increase in ACV dermis exposure compared to the neutral cream formulations without any additional sign of skin irritation. In conclusion, iontophoresis of ACV pH-11 gels provides higher ACV concentrations in the dermis than iontophoresis of neutral cream formulations, which could result in a better clinical outcome.

Quantification and prediction of skin pharmacokinetics of amoxicillin and cefuroxime

The purpose of this project was to develop and validate a pharmacokinetic model and to quantify the rate and extent of distribution between plasma and skin of two β‐lactam antibiotics, amoxicillin (AMX) and cefuroxime (CFX), which are frequently administered systemically to treat skin and skin structure infections. Dosing regimens are usually based on plasma concentration, however, concentrations at the target site are better correlated with the effect. For each antibiotic, three different i.v. bolus doses were administered to three female rabbits according to a randomized cross‐over design and plasma samples were collected serially. Skin concentrations were obtained by continuous microdialysis. Skin and unbound plasma concentrations were fitted simultaneously using a semi‐physiological model and the transfer constants plasma/skin (Kin) and skin/plasma (Kout) were estimated. Kin and Kout were then used to predict skin concentrations from the plasma levels obtained from an oral administration of AMX or from an i.v. bolus of CFX. The predicted skin profiles were similar to those measured by microdialysis during the actual experiments. In conclusion, this study shows that it is possible to generate a reasonable prediction of skin pharmacokinetics from any plasma level once a careful characterization of the transfer process between plasma and skin has been made. Copyright

Quantification of dermal and transdermal delivery of meloxicam gels in rabbits

Background: This study was designed to quantify the effects of penetration enhancers on systemic bioavailability of 0.3% meloxicam (MLX) hydroxypropylcellulose gels. Cutaneous microdialysis was also performed to assess dermis availability and to better understand the penetration process. The gels tested were a 1% oleic acid gel, a 5% menthol gel, and a control gel without penetration enhancers. Methods: To assess systemic bioavailability, three female rabbits received according to a crossover design 0.135 g/cm2 of gel applied to a 7.5 × 7.5 cm area of their shaved back and a short (5 min) infusion of 1 mg. In each experiment, blood samples were collected serially for 36 h and analyzed by a validated HPLC method. For skin bioavailability studies, 0.135 g/cm2 of the same gels were applied to a 1 × 2 cm area on top of a microdialysis probe previously inserted in the dermis. Dialysate samples were collected for 6 h every 30 min. Results: Systemically, the 5% menthol gel delivered 3.93 ± 0.85 mg of MLX versus the 1.41 ± 0.24 mg of the oleic acid gel. Only traces of MLX were detectable from the control gel. In dermis, substantial concentrations of MLX were detected only after the application of the menthol gel, whereas skin concentration from the control gel and the 1% oleic acid gel were always below the lowest limit of quantification (LLOQ). Conclusions: The 5% menthol gel can possibly deliver therapeutically relevant amount of MLX in vivo. Dermis concentrations can be predictive of systemic plasma levels.

Effect of microporation on passive and iontophoretic delivery of diclofenac sodium

Abstract Skin pretreatment with a microneedle roller (microporation (MP)) appears a simple and inexpensive technique to increase transdermal delivery of topically applied drug products. This study investigates the effect of MP on the passive and iontophoretic delivery of diclofenac (DCF) by quantifying dermis and plasma levels of DCF in a rabbit model. New Zealand albino female rabbits received either: (i) a topical application of 4 g of Voltaren® 1% gel with or without pretreatment with a microroller (0.5 mm needle length; density 23 microneedles per cm2 area) or (ii) a DCF solution (40 mg/2.5 mL) via iontophoresis (IOMED transQE medium size patch), with or without microroller pretreatment. A 300 µA/cm2 cathodic current was applied for 20 min for a total of 80 mA. DCF concentrations were monitored in dermis with microdialysis sampling every 20 min for 5 h. Plasma samples were collected over the same period. In the passive delivery studies, microroller pretreatment increased Cmax by 1.5- and 2.0-fold in skin and plasma, respectively, and AUC by 1.5- and 2.4-fold in skin and plasma, respectively. In the iontophoresis delivery studies, microporation increased Cmax by 2.0-fold both in skin and in plasma, and AUC by 1.1- and 1.8-fold in skin and plasma, respectively. In conclusion, microneedle pretreatment increased significantly the systemic exposure of DCF from either passive or iontophoretic delivery, whereas the effect in skin was less pronounced.

Development and in-vivo evaluation of ondansetron gels for transdermal delivery

Abstract Nausea and vomiting are some of the major side effects caused by certain drug therapies, e.g. chemotherapy, radiotherapy and general anesthesia. Because of the nature of the symptoms, oral delivery is inappropriate, while intravenous administration may be unpractical. The aim of the present study was to develop a transdermal gel (2% Klucel®) for ondansetron, a first line 5-HT3-receptor-antagonist antiemetic. The effects of the penetration enhancer camphor and isopropyl-myristate (IPM) were first investigated in-vitro using modified Franz diffusion-cells and then tested in-vivo in a rabbit model by measuring skin and plasma concentrations. Since a disadvantage of transdermal delivery is a prolonged lag-time, the effect of skin treatment with a micro-needle roller was tested. The in-vitro permeation studies through excised porcine ear skin showed that the presence of 2.5% camphor or IPM increased steady state flux by 1.2- and 2.5-fold, respectively, compared to the control gel. Ondansetron was not detectable in either skin or plasma following in-vivo application of the base-gel, whereas the camphor gel and IPM gel delivered 20 and 81 µg/cm2 of ondansetron, respectively. Microporation led to an increase in plasma Cmax and AUC by 10.47 ± 1.68-fold and 9.31 ± 4.91-fold, respectively, for the camphor gel, and by 2.31 ± 0.53-fold and 1.59 ± 0.38-fold, respectively for the IPM gel. In conclusion, the 2.5% IPM gel demonstrated optimal in-vivo transdermal flux. Skin pretreatment with a micro-needle roller slightly improved the delivery of the IPM gel, whereas dramatically increased the transdermal delivery of the camphor gel.

Permeability and Retention Studies of (-)Epicatechin Gel Formulations in Human Cadaver Skin

ABSTRACT (-)Epicatechin (EC) is a major antioxidant component of grape seed extract which has become increasingly popular in topical skin preparations. This study assessed the following: (1) the permeability through cellulose membranes of EC in three different gel formulations (Carbopol®940, Klucel®, and Ultrez™10); (2) the effect of three different antioxidants (butylated hydroxytoluene (BHT), alpha-tocopherol (VE), and ascorbic acid (AA)) on the stability and penetration properties of EC; and (3) the permeability and retention of EC in Ultrez™10 gels, supplemented with BHT or VE, on human cadaver skin. Permeability studies through cellulose membranes showed that different gelling agents do not significantly affect the permeability of EC (n = 7/gel; p > 0.05). BHT and VE have antioxidant properties superior to AA (p < 0.05) and preserve 100% of the initial content of EC for 28 days. Permeation studies on cadaver human skin, following application of two anhydrous gel formulations (0.5% EC in Ultrez™10 containing BHT or VE), showed that EC was not detectable in the receiving solution. However, the EC amount in viable skin increased with time, indicating that EC penetrated and was retained in the upper part of the skin for approximately 1% and 3% of the dose for the formulations containing BHT and VE, respectively.

Permeation study of five formulations of alpha-tocopherol acetate through human cadaver skin.

Alpha-tocopherol (AT) is the vitamin E homologue with the highest in vivo biological activity. AT protects against the carcinogenic and mutagenic activity of ionizing radiation and chemical agents, and possibly against UV-induced cutaneous damage. For stability consideration, alpha-tocopherol is usually used as its prodrug ester, alpha-tocopherol acetate (ATA), which once absorbed into the skin is hydrolyzed to alpha-tocopherol, the active form. The objective of this research was to characterize in vitro the permeation properties of ATA from various solutions and gel formulations. Permeation studies were conducted using modified Franz diffusion cells and human cadaver skin as the membrane. Specifically, 5% (w/w) alpha-tocopherol acetate was formulated in the following vehicles: ethanol, isopropyl myristate, light mineral oil, 1% Klucel gel in ethanol, and 3% Klucel gel in ethanol (w/w). The receiver temperature was 37 degrees C. Samples from the receiver were collected at 2, 4, 6, 8, 12, 24, 30, 36, and 48 hours and analyzed by HPLC for concentrations of alpha-tocopherol acetate and alpha-tocopherol. The permeabilities of ATA through human cadaver skin were 1.0x10(-4), 1.1x10(-2), 1.4x10(-4), 2.1x10(-4), and 4.7x10(-4) cm/h for the ethanol solution, isopropyl myristate solution, light mineral oil solution, 1% Klucel gel, and 3% Klucel gel, respectively. The results show that the formulation had relatively minor effects on the permeability coefficients of ATA through cadaver skin in all cases except for the isopropyl myristate solution.