Grazia Stagni

Despite its widespread and long term use, the effectiveness of iontophoresis to increase the delivery of dexamethasone sodium phosphate (DSP) remains controversial. The goal of this study was to quantitatively compare the DSP concentrations in dermis' dialysates in two delivery scenarios: with and without iontophoresis. Interstitial fluid concentrations were measured by cutaneous microdialysis. Passive and active iontophoresis were applied simultaneously on the skin of the forearm in eight healthy adult participants using each participant as his/her own control. The iontophoresis apparatus and procedures were identical to those used in common clinical practice. Iontophoresis electrodes were loaded with 2 mL of 4.4 mg/mL of preservative-free DSP solution. Electric current (4 mA) was applied for 20 min. Dialysate samples were collected for 2 h and analyzed for DSP and its active metabolite dexamethasone (DXM). Seven out of eight iontophoresis sites contained quantifiable levels of DSP and DXM, whereas none of the samples collected at the passive site contained either form of the drug. In conclusion, this study demonstrates that iontophoresis significantly (p < 0.0001) increases delivery of DSP to the dermis compared with passive delivery of the same, and that microdialysis can be used to monitor DSP delivery and DXM formation in skin.

Meloxicam (MLX) was formulated as a 0.3% hydroxypropylcellulose (Klucel) gel. The effect of four different combinations of co-solvents (ethanol, glycol-PEG-400, propylene glycol, and water) on MLX permeability was determined in vitro throughout isopropyl myristate (IPM)-saturated cellulose membranes. The gel consisting of 2.5% Klucel, propylene glycol, ethanol, and water (1:1:1) showed superior permeability properties and it was selected as the base-gel to investigate the effect of three levels of the penetration enhancers: dimethylsulfoxide (1, 5, and 10% DMSO), tween20 (1, 2, and 5% TW20), oleic acid (0.4, 1, and 5% OA), and menthol (1, 2.5, and 5% MT). In vitro permeability was determined throughout IPM-saturated cellulose membranes and human cadaver skin. DMSO and TW20 did not improve permeability of MLX compared to the control gel at any of the levels tested. Menthol produced a statistically significant (P<0.001), dose proportional increase in MLX flux with a peak at 5% (2.4...

Amoxicillin (AMX) and cefuroxime (CFX) are antibiotics used often to treat skin bacterial infections. Typically, high oral doses are required to achieve minimum inhibitory concentration (MIC) at the site of infection that may affect only a very small area of skin. To lower side effects and increase therapeutic effectiveness, the percutaneous absorption and retention of AMX and CFX administered by iontophoresis was investigated in a rabbit model by measuring dermis concentrations via microdialysis. Iontophoresis was performed using a stainless steel electrode and a non-woven polypropylene pad. The cartridge pad was soaked with a solution of AMX in glycerin or of CFX in glycerin/water (60:40). Constant current density of 0, 100, 200 or 300 µA/cm(2) was applied for 60 min. For AMX, therapeutically effective skin concentrations were detected immediately after the application of electrical current for any of the current density tested and remained above it for at least 2 h from the end of iontophoresis. For CFX, skin concentrations rose above MIC only at the higher current densities and fell below the MIC by the end of the experiment. Iontophoresis is a promising method to obtain a fast and sustained concentration of AMX and CFX in skin.

The aim of this study was to characterize and compare the pharmacokinetics of acyclovir (ACV) in skin and plasma after iontophoresis, i.v.-bolus, and ointment administrations in rabbit. On five occasions, each separated by at least 1-week washout, rabbits received a 10 mg/kg dose of ACV as i.v.-bolus, ACV iontophoresis for 1 h at different current densities (100, 200, 300 microA/cm2) or a commercially available ointment for two hours. Blood samples were collected serially up to 6 h. Skin ACV concentrations were monitored via microdialysis using linear microdialysis probes (1 cm window). Cathodic iontophoresis was performed using commercially available patches (10 cm2 contact area). Following i.v.-bolus, C(max) in skin occurred with a delay of 38 +/- 4 min compared with plasma. No quantifiable concentration of ACV was detected in the skin on passive drug delivery. Following iontophoresis, skin exposure to ACV was 40, 22, and 11% of that following i.v.-bolus. Conversely, systemic expo...

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...

During dynamic exercise in the heat, increases in skin blood flow are attenuated in hypertensive subjects when compared with normotensive subjects. We studied responses to passive heat stress (water-perfused suits) in eight hypertensive and eight normotensive subjects. Forearm blood flow was measured by venous-occlusion plethysmography, mean arterial pressure (MAP) was measured by Finapres, and forearm vascular conductance (FVC) was calculated. Bretylium tosylate (BT) iontophoresis was used to block active vasoconstriction in a small area of skin. Skin blood flow was indexed by laser-Doppler flowmetry at BT-treated and untreated sites, and cutaneous vascular conductance was calculated. In normothermia, FVC was lower in hypertensive than in normotensive subjects (P < 0.01). During heat stress, FVC rose to similar levels in both groups (P > 0.80); concurrent cutaneous vascular conductance increases were unaffected by BT treatment (P > 0.60). MAP was greater in hypertensive th...

Thioridazine (TDZ) is associated with an increased risk of falls. The purpose of this study was to determine whether (1) thioridazine increases Biomechanics Force Platform (BFP) measures of sway in a dose-related manner, (2) there is a difference in sway between young and old men, (3) there is a correlation between sway and orthostatic changes in BP and HR. Seven younger (aged 20-42) and five older (aged 70-76) healthy male volunteers received, in a randomized order double-blind design, a single oral dose of 0, 25, and 50 mg of TDZ on three separate days at least 7 days apart and 75 mg on the fourth day of the study. Sway and blood pressure were measured for 24 hours. A general clinical research center. Biomechanics force platform measures of postural sway were measured as the movement of the center of pressure. The elliptical area (EA) and average velocity (AV) were calculated with eyes open and eyes closed. Blood pressure and heart rate were measured for 5 minutes supine and 5 min...

A novel method is described for assessing drug bioavailability from pharmacologic data. The method is based upon a generalized model for the relationship between the observed effect (E) and the input rate (f): E = phi (ce delta * f), where * denotes convolution, ce delta is effect site unit impulse response ("amount" of drug at the effect site resulting from the instantaneous input of a unit amount of drug) and phi is transduction function (relates "amount" of drug at the effect site to E). The functions phi and ce delta are expressed as cubic splines for maximum versatility. Pharmacologic data collected after the administration of two different doses by i.v. infusion are analyzed simultaneously to estimate the function parameters. This experimental design addresses the fact that phi and ce delta cannot be uniquely estimated from the results of a single dose experiment. The unknown f from a test treatment is then estimated by applying an implicit deconvolution me...

A new method and experimental design are presented to unambiguously estimate the transduction function (phi) and the conduction function (psi) of the generalized pharmacodynamic model: E = phi (psi * r), when measured pharmacokinetic response r is (i) drug plasma concentration and (ii) drug input rate into the systemic circulation. phi relates the observed pharmacologic effect E to the concentration at the effect site: ce = (psi * r), psi defines transfer of drug from plasma site to effect site or from input site to effect site, and * represents the convolution integral. The model functions psi and phi were expressed as cubic splines giving a very flexible description of those processes which is not biased by the structured assumptions of more conventional models, e.g., effect compartment models. The experimental design proposed addresses the problem of ambiguous identification of the model functions typical of these models; that is, there is more than one pair of very different fun...

An improved HPLC method for the simultaneous determination of the enantiomers of verapamil (V) and its major metabolite norverapamil (NV) in human plasma samples is presented. NV is acetylated immediately to N-acetylnorverapamil (ANV) in the extraction solvent (2% butanol in hexane). Acetylation is so rapid that it does not delay sample processing. ANV and V enantiomers are then separated on an alpha 1-acid glycoprotein chiral column with a mobile phase of phosphate buffer (0.01 M, pH 6.65) and acetonitrile. The fluorescence detector wavelengths are set at 227 nm for excitation and 308 nm for emission. Introduction of the internal standard (I.S.) (+)-glaucine improves accuracy, precision and robustness of the method. The assay is sensitive and specific. Baseline separation is achieved for both V and ANV. Limits of quantitation are 3 ng/ml for V and 2 ng/ml for NV (single enantiomer) with precision and accuracy better than 15% at those levels. Detector response is linear in the range...

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 cm(2) area) or (ii) a DCF solution (40 mg/2.5 mL) via iontophoresis (IOMED transQ(E) medium size patch), with or without microroller pretreatment. A 300 µA/cm(2) 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....

Betaxolol is a cardioselective beta-adrenergic antagonist effective in the treatment of hypertension. The pharmacokinetic behavior of betaxolol enantiomers in healthy male subjects is reported. Betaxolol enantiomer concentrations were determined in samples collected up to 48 h after iv administration of a 10-mg dose over a 30-min period by constant-rate infusion in 12 subjects and after oral administration of 40-mg capsules to eight of the same subjects. Betaxolol extracted from whole blood was reacted with (+) or (-)-1-naphthylethyl isocyanate. The resulting diastereoisomeric derivatives were analyzed by reversed-phase HPLC with fluorimetric detection. Following the iv dose, there were no differences in clearance or volume of distribution for the two enantiomers (15.6 +/- 4.4 versus 16.4 +/- 4.1 L/h and 342 +/- 62 versus 340 +/- 65 L, respectively). Likewise, after the oral dose, there were no differences in the maximum concentration, time of maximum concentration, bioavailability, or apparent absorption rate constant (41.0 +/- 8.6 versus 42.0 +/- 7.0 ng/mL, 214 +/- 59 versus 215 +/- 56 min, 0.89 +/- 0.26 versus 0.94 +/- 0.23, and 1.0 +/- 0.6 versus 1.2 +/- 0.6 h-1, respectively). Thus, the pharmacokinetic behavior of racemic betaxolol accurately reflects the behavior of betaxolol enantiomers in this subject group.

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. 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. 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. 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.

Amitriptyline (AMT) is a tricyclic antidepressant with demonstrated local analgesic effects in human skin. We investigated the feasibility and mechanisms of iontophoretic delivery of AMT to rabbit dermis and plasma. Two microdialysis probes were inserted into the upper dorsal shaved skin of tranquilized rabbits. After 1 hour, an iontophoresis cartridge was placed on top of one probe. The cartridge consisted of a stainless steel electrode covered with a pad that was filled with a 4.3 % AMT glycerin/water (50:50). Iontophoresis was performed at 100, 200, or 300 microA/cm(2) constant-current density for 60 minutes. Dialysate samples were collected every 8 minutes for 3 hours and analyzed for AMT via a validated high-performance liquid chromatographic assay. Retrodialysis was performed at the other site. Blood samples were collected serially for 4 hours. In vivo retrodialysis recovery was 89 +/- 2%. AMT skin exposure increased non-proportionally with current density: AUCs were 19 +/- 7, 119 +/- 56, and 615 +/- 302 mg/L/min for the 100, 200, and 300 muA/cm(2), respectively, and C(max) were 107 +/- 15, 1070 +/- 537, and 5870 +/- 1289 microg/L. In vivo plasma concentrations were always below LLOQ (0.1 microg/mL). AMT can be administered by iontophoresis and produces significant skin concentrations and negligible plasma levels.