The influence of cosolvents on the in-vitro percutaneous penetration of diclofenac sodium from a gel system

Non-Invasive Extraction of Gabapentin for Therapeutic Drug Monitoring by Reverse Iontophoresis: Effect of pH, Ionic Strength, and Polyethylene Glycol 400 in the Receiving Medium

Background:

Monitoring of plasma concentrations is a necessity for narrow therapeutic index potent drugs. Development of non-invasive methods can save the patients from the trauma of needles and hence is considered as a research priority.

Introduction:

Gabapentin, an anti-epileptic drug requires therapeutic monitoring because of its narrow therapeutic index. The objective of the study was to develop a suitable method for the non-invasive extraction of gabapentin for the same.

Methods:

Transdermal reverse iontophoresis was performed using pig ear skin as a barrier membrane. Three compartment iontophoretic cells were used for the extraction study. Extractions were carried out under low intensity electric field (current intensity- 0.5 mA/cm2, electrical field approximately 5 V). The donor compartment was charged with aqueous gabapentin (10 µg/ml in phosphate buffer of pH 7.4). For studying the effect of receiving vehicle (pH, ionic strength, and enhancer) on the extraction efficiency of gabapentin, the two receiver chambers were charged with media having varying concentration of these factors. Drug content was determined by HPLC.

Results:

Compared to other pHs, cumulative extraction of gabapentin at pH 5 was significantly higher at both anode and cathode (p<0.001). At low ionic strength, extraction of gabapentin increased linearly with the increase in concentration of ions up to a certain value but at very high ionic strength the pattern reversed. Similar results were obtained with enhancer (polyethylene glycol 400). Extraction increased with increase in polyethylene glycol 400 up to 3% and then decreased.

Conclusion:

Extraction flux can be optimized by manipulation of the receiver media.

Design, Development, and Optimization of Dexibuprofen Microemulsion Based Transdermal Reservoir Patches for Controlled Drug Delivery

The aim of the study was to develop a reservoir-type transdermal patch for a controlled delivery of dexibuprofen and to evaluate its in vivo anti-inflammatory activity in Albino Wistar rats. In order to develop these patches, six formulations of dexibuprofen microemulsion comprising ethyl oleate, Tween 80: PG (2 : 1), and water were prepared by simplex lattice design and characterized. The reservoir compartment was filled with these microemulsions and in vitro release and skin permeation were assessed. The optimized patch was obtained on the basis of the responses: Q₂₄ and flux. The impact of drug loading, surface area, membrane thickness, adhesive, and agitation speed on drug release and permeation was also studied. The skin sensitivity reaction and in vivo anti-inflammatory activity of optimized patch were evaluated. Stability study at three different temperatures for three months was carried out. The result suggests that a membrane based patch with zero-order release rate, Q₂₄ of 79.13 ± 3.08%, and maximum flux of 331.17 µg/cm²h can be obtained exhibiting suitable anti-inflammatory activity with no visible skin sensitivity reaction. The outcomes of stability study recommend storage of patches at 4°C having shelf-life of 6.14 months. The study demonstrates that the reservoir-type transdermal patch of dexibuprofen microemulsion has a potential of delivering drug across skin in controlled manner with required anti-inflammatory activity.

Enhanced dissolution and skin permeation profiles of epalrestat with β-cyclodextrin derivatives using a cogrinding method

Epalrestat (EPL) is a water-insoluble drug (14μM) that inhibits aldose reductase. This study investigated the interactions between β-cyclodextrin (CD) derivatives and EPL to determine the solubilizing effect on EPL from phase solubility diagrams. We improved the solubility of EPL in water by adding β-CD derivatives. Moreover, the solubility of EPL mixed with β-CD derivatives by cogrinding in a ball mill method was about 2-3 times higher than those of EPL with the same CD concentration (5mM) calculated from phase solubility diagrams. In addition, we investigated the effect of β-CD derivatives on in vitro percutaneous absorption of EPL through hairless mouse skin. Among the coground mixtures of EPL and β-CD derivatives, the mixture containing methyl (ME)-β-CD showed the strongest enhancement of EPL skin permeation. Furthermore, adding 10wt% urea as a skin permeation enhancer after cogrinding with ME-β-CD improved the flux of EPL 300 times compared to the flux of EPL alone. This result indicates the ME-β-CD ground mixture system with urea has potential as a new transdermal drug delivery system of EPL for diabetic neuropathy.

Design and Evaluation of Topical Diclofenac Sodium Gel Using Hot Melt Extrusion Technology as a Continuous Manufacturing Process with Kolliphor® P407

The aim of the present context was to develop and evaluate a Kolliphor® P407-based transdermal gel formulation of diclofenac sodium by hot melt extrusion (HME) technology; central composite design was used to optimize the formulation process. In this study, we have explored first time ever HME as an industrially feasible and continuous manufacturing technology for the manufacturing of gel formulation using Kolliphor® P407 and Kollisolv® PEG400 as a gel base. Diclofenac sodium was used as a model drug. The HME parameters such as feeding rate, screw speed, and barrel temperature were crucial for the semisolid product development, and were optimized after preliminary trials. For the processing of the gel formulation by HME, a modified screw design was used to obtain a uniform product. The obtained product was evaluated for physicochemical characterization such as differential scanning calorimetry (DSC), X-ray diffraction (XRD), pH measurement, rheology, surface tension, and texture profile analysis. Moreover, it was analyzed for general appearance, spreadibility, surface morphology, and drug content. The optimized gel formulation showed homogeneity and transparent film when applied on a glass slide under microscope, pH was 7.02 and uniform drug content of 100.04 ± 2.74 (SD = 3). The DSC and XRD analysis of the HME gel formulation showed complete melting of crystalline API into an amorphous form. The Kolliphor® P407 and Kollisolv® PEG400 formed excellent gel formulation using HME with consistent viscoelastic properties of the product. An improved drug release was found for the HME gel, which showed a 100% drug release than that of a marketed product which showed only 88% of drug release at the end of 12 h. The Flux value of the HME gel was 106 than that of a marketed formulation, which showed only about 60 value, inferring a significant difference (P < 0.05) at the end of 1 h. This study demonstrates a novel application of the hot melt extrusion process for manufacturing of topical semisolid products.

Enhancement of skin permeation of vitamin C using vibrating microneedles

This study was performed to evaluate the use of vibrating microneedles for the transdermal delivery of vitamin C. The microneedles were designed to vibrate at three levels of intensity. In vitro permeation by vitamin C was evaluated according to the specific conditions such as vibration intensity (levels 1, 2 and 3), application time (1, 3, 5, 7 and 10 min), and application power (500, 700 and 1,000 g). The highest permeation of vitamin C was observed at level 3 of vibration intensity, 5 min of application, and 1,000 g of application power. Vitamin C gel showed no cytotoxic effect against Pam212 cells or skin irritation effects. A pharmacokinetic study of the gel in rats was conducted under optimized conditions. The AUC₀-_∞ and C_max increased 1.35-fold and 1.44-fold, respectively, compared with those after vitamin C gel without application with vibrating microneedles. The present study suggests that vibrating microneedles can be used to facilitate the skin permeability of vitamin C under optimal conditions.

Evaluation of skin permeation and analgesic activity effects of carbopol lornoxicam topical gels containing penetration enhancer

The current study was designed to develop a topical gel formulation for improved skin penetration of lornoxicam (LOR) for enhancement of its analgesic activity. Moreover, the effect of different penetration enhancers on LOR was studied. The LOR gel formulations were prepared by using hydroxylpropyl methylcellulose (HPMC) and carbopol. The carbopol gels in presence of propylene glycol (PG) and ethanol were developed. The formulated gels were characterized for pH, viscosity, and LOR release using Franz diffusion cells. Also, in vitro skin permeation of LOR was conducted. The effect of hydroxypropyl β-cyclodextrin (HP β-CD), beta-cyclodextrin (β-CD), Tween 80, and oleic acid on LOR permeation was evaluated. The optimized LOR gel formulation (LORF8) showed the highest flux (14.31 μg/cm(2)/h) with ER of 18.34 when compared to LORF3. Incorporation of PG and HP β-CD in gel formulation (LORF8) enhanced the permeation of LOR significantly. It was observed that LORF3 and LORF8 show similar analgesic activity compared to marketed LOR injection (Xefo). This work shows that LOR can be formulated into carbopol gel in presence of PG and HP β-CD and may be promising in enhancing permeation.

A drug-in-adhesive matrix based on thermoplastic elastomer: evaluation of percutaneous absorption, adhesion, and skin irritation

A novel drug-in-adhesive matrix was designed and prepared. A thermoplastic elastomer, styrene-isoprene-styrene (SIS) block copolymer, in combination with tackifying resin and plasticizer, was employed to compose the matrix. Capsaicin was selected as the model drug. The drug percutaneous absorption, adhesion properties, and skin irritation were investigated. The results suggested that the diffusion through SIS matrix was the rate-limiting step of capsaicin percutaneous absorption. [SI] content in SIS and SIS proportions put important effects on drug penetration and adhesion properties. The chemical enhancers had strong interactions with the matrix and gave small effect on enhancement of drug skin permeation. The in vivo absorption of samples showed low drug plasma peaks and a steady and constant plasma level for a long period. These results suggested that the possible side effects of drug were attenuated, and the pharmacological effects were enhanced with an extended therapeutic period after application of SIS matrix. The significant differences in pharmacokinetic parameters produced by different formulations demonstrated the influences of SIS copolymer on drug penetrability. Furthermore, the result of skin toxicity test showed that no skin irritation occurred in guinea pig skin after transdermal administration of formulations.

Evaluation of glycofurol-based gel as a new vehicle for topical application of naproxen

In view of the good skin tolerability, glycofurol was used as a vehicle-based gel, and its effect in the topical penetration of Naproxen (NAP) was investigated. The aims of this study were to develop a suitable gel with bioadhesive property, spreadability, and viscosity for topical anti-inflammatory effect. Three gelling and adhesive agents were examined: Carbopol 974P, Gantrez AN 119, and polyvinylpyrollidone K30. Skin permeation rates and lag times of NAP were evaluated using the Franz-type diffusion cell in order to optimize the gel formulation. The permeation rate of NAP-based gel across the excised rat skin was investigated. A significant increase in permeability parameters such as steady-state flux (J(ss)), permeability coefficient (K(p)), and penetration index (PI) was observed in optimized formulation containing 2% Transcutol as an permeation enhancer. From skin irritation test, it was concluded that the optimized novel glycofurol-based gel formulation was safe to be used for topical drug delivery. The developed glycofurol-based gel appeared promising for dermal and transdermal delivery of naproxen and could be applicable with water-insoluble drugs, which would circumvent most of the problems associated with drug therapy.

Ketorolac trometamol topical formulations: release behaviour, physical characterization, skin permeation, efficacy and gastric safety

Objectives

The objective of this study was to improve systemic delivery of the highly analgesic ketorolac trometamol (ketorolac tromethamine) via the transdermal route, through cost-effective topical formulations, to avoid most of the problems associated with ketorolac trometamol therapy.

Methods

In-vitro release behaviour of the drug from different microemulsion and emulgel formulations was evaluated. E2 emulgel (based on isopropyl myristate as penetration enhancer) and E7 emulgel (based on Brij 92 as penetration enhancer) were evaluated for their physical properties, rat skin permeation, in-vivo analgesic effect (hot-plate test and the paw pressure test), acute and chronic anti-inflammatory activity and gastric safety.

Key findings

Isopropyl myristate and the synergistic effect of the two known penetration enhancers (propylene glycol and Brij 92) significantly modulated drug permeation and may be a promising approach for the transdermal delivery of ketorolac trometamol and other drugs. Selected in-vivo tested formulae (E2 and E7) caused significantly less ulcer score and less gastric erosion compared with oral ketorolac trometamol. E7 showed significantly higher analgesic and anti-inflammatory activity compared with E2 with no significant difference compared with oral ketorolac trometamol.

Conclusions

The developed ketorolac trometamol E7 emulgel appeared promising for dermal and transdermal delivery of ketorolac trometamol, which would circumvent most of the problems associated with drug therapy.

Formulation optimization and in situ absorption in rat intestinal tract of quercetin-loaded microemulsion

A new microemulsion system has been developed to increase the solubility and oral absorption of quercetin, a poorly water-soluble drug. The formulation of quercetin-loaded microemulsion was optimized by a simplex lattice experiment design. The optimized microemulsion formulation consisted of oil (7%, w/w), surfactant (48%, w/w), and cosurfactant (45%, w/w). Under this condition, the mean droplet diameter of microemulsion was 38.9 nm and solubility of quercetin in the microemulsion was 4.138 mg/ml. The in situ absorption property of quercetin-loaded microemulsion in rat intestine was studied and the results showed there was significant difference in absorption parameters such as K(a), t(1/2) and uptake percentages between microemulsion and micelle solution containing quercetin. The study on absorption percentage in different regions of rat intestine attested that the colon had the best permeability, followed by ileum, duodenum in order. It can be concluded that microemulsion can improve the solubility and oral absorption of quercetin, a poorly water-soluble drug.

Testosterone solid lipid microparticles for transdermal drug delivery. Formulation and physicochemical characterization

PURPOSE

The main objective of the study was to formulate and characterize testosterone (TS) solid lipid microparticles (SLM) to be applied as a transdermal delivery system.

METHODS

Testosterone SLMs were formulated using an emulsion melt homogenization method. Various types and concentrations of fatty materials, namely glyceryl monostearate (GM), glyceryl distearate (GD), stearic acid (SA) and glyceryl behanate (GB) were used. The formulations contained 2.5 or 5 mg TS g(-1). Morphology, particle size, entrapment efficiency (EE), rheological properties and thermal behaviour of the prepared SLM were examined. In vitro release characteristics of TS from various prepared SLM were also evaluated over 24 h using a vertical Franz diffusion cell. In addition, the effect of storage and freeze-drying on particle size and release pattern of TS from the selected formulation was evaluated.

RESULTS

The results indicated that the type of lipid affected the morphology and particle size of SLM. A relatively high drug percentage entrapment efficiency ranging from 80.7-95.7% was obtained. Rheological studies showed plastic flow characteristics of the prepared formulations. DSC examination revealed that TS existed in amorphous form in the prepared SLM. Release studies revealed the following rank order of TS permeation through cellophane membrane after application of various formulations: 5% GM < 5% GD < 5% SA < 5% GB < 2.5% GM < 2.5% SA < 10% GD < 10% GB. The drug permeation through excised abdomen rat skin after application of 10% GB-2.5 mg TS g(-1) SLM was lower than that permeated through cellophane membrane. Moreover, SLM containing 10% GB-2.5 mg TS g(-1) stored at 5 degrees C showed good stability as indicated by the release study and particle size analysis. Trehalose showed high potential as a cryoprotectant during freeze drying of the selected SLM formulation.

CONCLUSIONS

The developed TS SLM delivery system seemed to be promising as a TS transdermal delivery system.

Development of lapachol topical formulation: anti-inflammatory study of a selected formulation

This study aimed at developing a topical formulation of lapachol, a compound isolated from various Bignoniaceae species and at evaluating its topical anti-inflammatory activity. The influence of the pharmaceutical form and different types of emulsifiers was evaluated by in-vitro release studies. The formulations showing the highest release rate were selected and assessed trough skin permeation and retention experiments. It was observed that the gel formulation provided significantly higher permeation and retained amount (3.9-fold) of lapachol as compared to the gel-cream formulation. Antinociceptive and antiedematogenic activities of the most promising formulation were also evaluated. Lapachol gel reduced the increase in hind-paw volume induced by carrageenan injection and reduced nociception produced by acetic acid (0.8% in water, i.p.) when used topically. These results suggest that topical delivery of lapachol from gel formulations may be an effective medication for both dermal and subdermal injuries.

Enhancement of iontophoretic transport of diphenhydramine hydrochloride thermosensitive gel by optimization of pH, polymer concentration, electrode design, and pulse rate

The purpose of the present study was to explore the passive and electrically assisted transdermal transport of diphenhydramine hydrochloride (DPH) by iontophoresis. For better bioavailability, better patient compliance, and enhanced delivery of DPH, an iontophoretic drug delivery system of a thermosensitive DPH gel was formulated using Lutrol F-127. The study was conducted using silver-silver chloride electrodes across hairless pig skin. The effects of pH, polymer concentration, electrode design, and pulse rate on the DPH permeation were investigated. The relationship between temperature, viscosity, and conductance of DPH was correlated using conductometry. Iontophoretic transport of DPH was found to increase with a decrease in the pH of the medium and an increase in the surface area of the electrode. Viscosity measurements and flux calculations indicated the suitability of the Lutrol gel for transdermal iontophoretic delivery of DPH. Anodal pulsed iontophoresis with disc electrode significantly increased the DPH skin permeation as compared with the passive controls.

Comparison of different water/oil microemulsions containing diclofenac sodium: preparation, characterization, release rate, and skin irritation studies

The aim of the present study was to make a comparison of the in vitro release rate of diclofenac sodium (DS) from microemulsion (M) vehicles containing soybean oil, nonionic surfactants (Brij 58 and Span 80), and different alcohols (ethanol [E], isopropyl alcohol [I], and propanol [P]) as cosurfactant. The optimum surfactant:cosurfactant (S:CoS) weight ratios and microemulsion areas were detected by the aid of phase diagrams. Three microemulsion formulations were selected, and their physicochemical properties were examined for the pH, viscosity, and conductivity. According to the release rate of DS, M prepared with P showed the significantly highest flux value (0.059 +/- 0.018 mg/cm(2)/h) among all formulations (P < .05). The conductivity results showed that DS-loaded microemulsions have higher conductivity values (18.8-20.2 microsiemens/cm) than unloaded formulations (16.9-17.9 microsiemens/cm), and loading DS into the formulation had no negative effect on system stability. Moreover, viscosity measurements were examined as a function of shear rate, and Newtonian fluid characterization was observed for each microemulsion system. All formulations had appropriate observed pH values varying from 6.70 to 6.85 for topical application. A skin irritation study was performed with microemulsions on human volunteers, and no visible reaction was observed with any of the formulations. In conclusion, M prepared with P may be a more appropriate formulation than the other 2 formulations studied as drug carrier for topical application.

Effect of Permeation Enhancers on the in Vitro Percutaneous Absorption of Pentazocine1)

The effect of permeation enhancers on the percutaneous absorption of pentazocine (PTZ) was investigated in excised hairless mice using Franz diffusion cells in vitro. The enhancing effect on the percutaneous absorption of PTZ from the isopropyl myristate (IPM) solution system was improved with glyceryl monocaprylate (GEFA-C(8)), which is a kind of glycerol ester of fatty acid (GEFA). The flux of PTZ through the skin was ca. 4 times higher compared with IPM alone, while a less enhancing effect of glyceryl dicaprylate (GEFA-DiC(8)) and glyceryl tricaprylate (GEFA-TriC(8)) on the skin permeation of PTZ was found. Moreover, maximum enhancement of PTZ flux was observed with glyceryl monocaproate (GEFA-C(6)) among various alkyl chains (C(2)-C(18)) of monoglycerides. These results indicated that the IPM solution system combination with GEFA may be used to develop a transdermal formulation with improved skin permeation of PTZ.

Transdermal delivery of diclofenac sodium through rat skin from various formulations

The aim of this study was to evaluate and compare the in vitro and in vivo transdermal potential of w/o microemulsion (M) and gel (G) bases for diclofenac sodium (DS). The effect of dimethyl sulfoxide (DMSO) as a penetration enhancer was also examined when it was added to the M formulation. To study the in vitro potential of these formulations, permeation studies were performed with Franz diffusion cells using excised dorsal rat skin. To investigate their in vivo performance, a carrageenan-induced rat paw edema model was used. The commercial formulation of DS (C) was used as a reference formulation. The results of the in vitro permeation studies and the paw edema tests were analyzed by repeated-measures analysis of variance. The in vitro permeation studies found that M was superior to G and C and that adding DMSO to M increased the permeation rate. The permeability coefficients (Kp) of DS from M and M+DMSO were higher (Kp = 4.9 x 10(-3) +/- 3.6 x 10(-4) cm/h and 5.3 x 10(-3) +/- 1.2 x 10(-3) cm/h, respectively) than the Kp of DS from C (Kp = 2.7 x 10(-3) +/- 7.3 x 10(-4) cm/h) and G (Kp = 4.5 x 10(-3) +/- 4.5 x 10(-5) cm/h). In the paw edema test, M showed the best permeation and effectiveness, and M+DMSO had nearly the same effect as M. The in vitro and in vivo studies showed that M could be a new, alternative dosage form for effective therapy.

In vitro and in vivo evaluation of topical formulations of spantide II

The purpose of this study was to develop and evaluate topical formulations of Spantide II, a neurokinin-1 receptor (NK-1R) antagonist, for the treatment of inflammatory skin disorders. Spantide II lotion and gel was formulated with and without n-methyl-2-pyrrolidone (NMP) as a penetration enhancer. The release of Spantide II from gels was evaluated using microporous polyethylene and polypropylene membranes in a Franz Diffusion cell setup. In vitro percutaneous absorption of Spantide II from lotion and gel formulations was evaluated using the above setup by replacing the membranes with hairless rat skin. The in vivo anti-inflammatory activity of Spantide II formulations was evaluated in an allergic contact dermatitis (ACD) mouse model. Among different gels studied, PF127 gel showed highest (70-fold) release of Spantide II compared with hydroxypropyl methylcellulose (HPMC) and hydroxypropyl cellulose (HPC) gels. Lotion and gel formulations with or without NMP showed no detectable levels of Spantide II in the receiver compartment of the Franz diffusion cell until 24 hours. However, Spantide II showed significant retention in epidermis and dermis from lotion and gel formulations at 24 hours. The dermal levels increased approximately 3.5- and 2-fold when the lotion and gel formulations contained NMP as compared with the formulation with no NMP (P < .05). The in vivo studies indicated that Spantide II formulations with NMP were effective in significantly reducing ACD response, similar to dexamethasone (0.5 mM). In conclusion, Spantide II was stable as a topical formulation and delivered to target skin tissue (epidermis and dermis) for the treatment of ACD. In addition this study supports the role of cutaneous neurosensory system in modulating inflammatory responses in the skin.

Release characteristics of anionic drug compounds from liquid crystalline gels

Liquid crystalline gels (LCG) offer the formulator dynamic and flexible vehicles, into which actives, enhancers and other adjuvants with a wide range of physicochemical properties can be incorporated. This is achievable because of the biphasic oil/water composition of the gel. In this paper, the suitability of an isotropic liquid crystalline gel is investigated for a range of anionic drug molecules, with particular emphasis on sodium diclofenac. Parameters, which have been investigated, include the mode of vehicle preparation, the effect of the concentration of the drug and how buffering the gel and/or the receptor medium affect the release profiles. Such profiles have been measured for the sodium salts of benzoate, salicylate and indomethacin. The passive release from the standard system was found to adhere to matrix-controlled diffusion. An increase in concentration leads to a non-linear increase in the cumulative release of sodium diclofenac from the gels. In direct contrast to the result reported for cationic salbutamol base, optimum release from the gel was achieved when neither the receptor medium nor the aqueous phase of the gel was buffered. The percentages released of the sodium salts of benzoate, salicylate and indomethacin, after 24 h, were determined to be 25, 26 and 19%, respectively, and these are significantly greater than the release of sodium diclofenac. This suggests that diclofenac undergoes ion-pairing or complexation within the gel, which inhibits its diffusion from the vehicle. Future papers will report on the incorporation of enhancers and the effects of iontophoresis on the release profiles of drugs from these gels, and ultimately on the transdermal transport of drugs from these vehicles across human and porcine skin.

In vitro percutaneous penetration of acyclovir from solvent systems and Carbopol 971-P hydrogels: influence of propylene glycol

The mechanism underlying propylene glycol (PG) effects on acyclovir (ACV) penetration through human epidermis were studied. Solvent systems and Carbopol gels containing increasing percentage of PG (from 0% to 70%, w/w) were used. Viscosity studies of both vehicles were carried out to characterise the influence of rheological behaviour. In solvent systems skin permeation values of ACV increase as the concentration of PG increase yielding a maximum enhancement ratio (ER = 10) for 70% PG. The release rate of ACV from gels was determined. Higuchi's model was used to estimate the apparent diffusion coefficient of the drug. These values show a decrease as the content of PG in the vehicle increases; this effect could be attributed to the increase of the viscosity in the diffusional pathway. When gels are used skin permeation values of ACV were smaller than those of the solvent systems. This could be attributed to the network structure created by the polymer that increases the length of the diffusional pathway. The maximum ER (= 6.8) was for Carbopol gel containing 50% PG. Therefore, these gels can be considered candidates for further research to confirm their usefulness as delivery systems for ACV topical formulations.

The Influence of Cosolvent Polarity on the Flow Properties of Hydroalcoholic Gels. Empirical Models

The aim of this study was to investigate the influence of cosolvent polarity on the rheological flow properties of aqueous and hydroalcoholic gels obtained from the Carbopol Ultrez 10 base and used for topical applications. Specifically, we have examined the effect of pH (range 4.0--7.0) on the consistency and flow properties of dispersed systems in water and mixtures--15 : 85% v/v of methanol : water, ethanol : water, n-propanol : water and n-butanol : water--at a constant polymer concentration of 0.3% w/w. The gels, which had decreasing polarity values in the jellifying medium, showed qualitatively similar flow behavior, characteristic of pseudoplastic systems, and all of the flow curves were adjusted to the Ostwald model. Sigmoidal dose response functions were calculated to describe the flow and consistency indexes as a function of pH. As a result, the influence of alcohol polarity on the polymer network has been assessed meaningfully using the empirical parameters obtained: maximum consistency index value (k(max)), pH value required for 50% development of polymer network (pH(50)), and asymptotic flow index value (n(min)) for the fully structured gels.

Noninvasive glucose monitoring by back diffusion via skin: chemical and physical enhancements

Blood glucose levels are routinely obtained by invasive and painful methods using glucose meters and test strips. The development of less invasive or non invasive techniques would be beneficial for diabetes patients. In this study, a noninvasive method was evaluated using the back diffusion of glucose across skin with or without permeation enhancement methods. An in vitro model was utilized. The stratum corneum (SC) was the predominant barrier for both back and forward diffusion of glucose across skin. Surfactants with various charges and essential oils (cyclic monoterpenes) were used as chemical enhancers to promote the back diffusion of glucose. A cationic surfactant (benzalkonium chloride) showed the highest enhancement, followed by anionic and nonionic surfactants. d-Limonene and 1,8-cineole dispersed in appropriate proportions of ethanol could enhance the glucose diffusion after pretreatment of the skin surface. Electroporation, defined as a physical method, significantly increased the amount of glucose that diffused back. The percentages of diffused glucose by 300 V (volts) and 500 V high voltage pulses on skin for 10 min were found to be 45 and 75 times greater than the control group, respectively.

Effect of enhancers and retarders on percutaneous absorption of flurbiprofen from hydrogels

The effect of enhancers/retarders on the transdermal absorption of flurbiprofen from cellulose hydrogels was studied in vitro. The release rate of flurbiprofen and the viscosity of hydrogel matrices were also examined. The flux of flurbiprofen from cellulose hydrogels approximated that from aqueous buffers, whereas the skin reservoir of flurbiprofen was lower with hydrogels. Incorporation of the cosolvents, propylene glycol (PG) and ethanol, did not significantly increase skin absorption of flurbiprofen. Ethanol even reduced the skin reservoir of the drug. Oleic acid, an unsaturated fatty acid, produced the largest skin reservoir of the drug when incorporated into the hydrogels. D-Limonene, a cyclic monoterpene, showed the greatest ability to enhance the flux of flurbiprofen. However, phospholipids as retarders markedly reduced the skin absorption of flurbiprofen. The mechanisms by which enhancers/retarders govern flurbiprofen permeation were elucidated by in vitro permeation studies using various skin types (enhancers/retarders-pretreated skin, stratum corneum (SC)-stripped skin, and delipidized skin) and histological examination. The results suggest different mechanisms and skin structural modifications caused by different enhancers/retarders.

Systematic study of the flow behaviour and mechanical properties of Carbopol Ultrez 10 hydroalcoholic gels

Flow behaviour and mechanical properties of 0:100, 15:85, and 30:70 v/v gelled ethanol:water mixtures are studied as a function of pH (4.0-7.0) and Carbopol Ultrez 10 concentration (0.1-0.5%). As previously reported individually for 30% v/v alcoholic Ultrez 10 gels, flow curves were adjusted to the Ostwald's model, and similar sigmoidal dose response functions were obtained to describe the pH dependence of consistency index and mechanical properties of the systems. The concentration dependence of flow indexes was also best adjusted to one-phase exponential decay functions. As a result, the influence of ethanol content on polymer network is meaningfully assessed by means of the obtained empirical parameters: bottom value of each variable (Y(max)), pH value required for a 50% polymer network development (pH(50)), and asymptotic flow index value for the fully structured gels (n(min)). Also, it is assessed the influence of cosolvent on the above-mentioned empirical variables, by studying pH-dependence of gelation in methanol:water, 1-propanol:water and 1-butanol:water 15:85% v/v mixtures. As a result, the alcohol induced variations in consistency and mechanical properties of hydroalcoholic gels were well correlated to modifications in the solubility parameter (delta(T)).

The effects of iontophoresis and electroporation on transdermal delivery of buprenorphine from solutions and hydrogels

The in-vitro permeation of buprenorphine across skin was investigated to assess the effects of iontophoresis and electroporation on drug permeation from solutions as well as from hydrogels. Iontophoresis (0.3 mA cm(-2)) increased the buprenorphine permeation from solution by a factor of 14.27 as compared with passive diffusion; the application of electroporation increased the buprenorphine permeation from solutions by a factor of 8.45. The permeation experiments using cellulose membrane and stratum corneum (SC)-stripped skin as permeation barriers suggested that the enhancement with iontophoresis was primarily due to strong electrophoretic drift of buprenorphine molecules, whereas the enhancement seen with electroporation was mainly attributed to the creation of transient aqueous pores in the SC layer. Application of high-voltage pulses followed by iontophoresis resulted in a shorter permeation onset time from both solutions and hydrogels as compared with iontophoresis or electroporation alone. The charge repulsion between buprenorphine and chitosan vehicles as well as the competition effects of counter-ions for carboxymethylcellulose (CMC)-based polymers may account for the different permeation rates under electrical field. This study demonstrates the feasibility of using hydrogels for delivery of buprenorphine under the application of iontophoresis or electroporation, separately or together.

In-vitro release of diclofenac diethylammonium from lipid-based formulations

This article presents the preparation and topical performance of some new lipid-based formulations of diclofenac, namely (a) a diclofenac aqueous gel containing mixed micelles (sodium cholate:egg lecithin molar ratio 0.55); (b) diclofenac lotion that contains soya lecithin, ethanol and buffer; and (c) diclofenac lipogel containing egg lecithin, isopropyl myristate, propylene glycol and ethanol. Gel formulations were prepared using Carbomer 934. Release of diclofenac from all formulations was monitored via dialysis through Spectra/por membrane into phosphate buffer (0.2 M pH=7.4) using a Franz cell. Drug release profile and diffusion coefficients were compared with brand formulation (Geigy's Vlotaren Emulgel). Statistical analysis of data show that the diffusion coefficient of the drug from these formulations rank according to the following order: Diclofenac lotion (D=5.308x10(-7) cm(2)/s) >lipogel (D=2.102 x 10(-7) cm(2)/s) >Voltaren Emulgel (1.518 x 10(-7) cm(2)/s) >aqueous gel mixed micelle (0.966 x 10(-7) cm(2)/s). These results show that diclofenac lotion and lipogel maybe more suitable formulations than the conventional topical dosage form.

In vitro topical application and in vivo pharmacodynamic evaluation of nonivamide hydrogels using Wistar rat as an animal model

Nonivamide, a so-called synthetic capsaicin, is a substitute for capsaicin which has a similar chemical structure and pharmacological activities as those of capsaicin. The purposes of this study were to explore the in vivo pharmacodynamic responses of nonivamide in hydrogels using Wistar rat as an animal model and to correlate the in vivo results with in vitro topical application. The incorporation of Pluronic F-127 polymer into hydrogels resulted in retarded release of nonivamide. Chitosan and carboxymethylcellulose hydrogels produced higher levels of in vitro nonivamide permeation and skin distribution. The in vivo effects of nonivamide on skin perturbation and vasodilation were found to differ depending on dose and duration after topical application. Quantification of transepidermal water loss was demonstrated to correlate with the measured in vitro skin distribution of nonivamide. The various doses of nonivamide in the hydrogels did not markedly influence erythematous reactions of skin as determined by colorimetric measurements. Hydrogel formulations of nonivamide delivered more drug to the skin and produced greater pharmacodynamic activities than did cream bases of capsaicin.

Transdermal delivery of triprolidine using TPX polymer membrane

Triprolidine-containing matrix was fabricated with poly(4-methyl-1-pentene) (TPX) polymer to control the release of the drug. Effect of penetration enhancer and stripping of skin on the permeation of triprolidine through the excised mouse skin was studied. Penetrating enhancers showed the increased flux probably due to the enhancing effect on the skin barrier, the stratum corneum. Among enhancers used such as glycols, fatty acids and non-ionic surfactants, polyoxyethylene-2-oleyl ether showed the best enhancement. The permeability of triprolidine was markedly increased with stripping the mouse skin to remove the stratum corneum, which acts as a barrier of skin permeation. For the controlling delivery of triprolidine, the TPX matrix containing permeation enhancer could be developed.

In vitro and in vivo evaluations of topically applied capsaicin and nonivamide from hydrogels

The purpose of this study was designed to investigate the in vitro and in vivo skin absorption of capsaicin and nonivamide from hydrogels. Various commercialized creams of capsaicin were also compared with hydrogels. Both skin stripping technique and Mexameter were applied to evaluate the level of capsaicin and nonivamide retained in stratum corneum (SC) and skin erythema in vivo. The partition of drug between skin and the hydrogel matrix was considered to play an important role in the permeation process. The in vitro permeation of capsaicin from hydrogels depends on the physicochemical nature and the concentration of the polymer used. The incorporation of nonionic Pluronic F-127 polymer into hydrogels resulted in a retarded release of capsaicin. On the other hand, the in vitro capsaicin permeation showed higher levels in cationic chitosan and anionic carboxymethyl cellulose (CMC) hydrogels than cream bases. The permeation of nonivamide was retarded at the late stage of in vitro application. The inter-subject variation was more significant in the in vivo study than in vitro skin permeation experiments. The cream induced in vivo skin erythema depending on the drug concentration, however, the dose-dependence was not observed in hydrogels. Nonivamide-treated skin showed stronger erythema than capsaicin-treated skin. The present study indicates that there is a moderate correlation between in vitro skin permeation and in vivo erythema responses of topically applied capsaicin and nonivamide. The correlation between drug amount in SC and skin erythema test in vivo was also observed.

Rheological characterization of hydroalcoholic gels--15% ethanol--of Carbopol Ultrez 10

The rheological behaviour of Carbopol Ultrez 10 ethanolic (15%) gels was studied as a function of two main variables: pH (4.0-7.0) and the polymer concentration (0.1-0.5%). Flow curves of all hydroalcoholic gels were adjusted to the Ostwald model. Sigmoidal dose response functions were obtained to describe the pH dependence of consistency index of the systems. The concentration dependence of flow indexes was best adjusted to one-phase exponential decay functions. Finally, by substituting in the power law expression, an empirical model is given to estimate viscosities of gels for any value of pH and polymer concentration in the ranges evaluated. As a result, the influence of the variables on polymer network is meaningfully assessed by means of the obtained empirical parameters: bottom value (Ymax), pH value required for a 50% polymer network development (pH50), and asymptotic flow index value for the fully structured gels (n(min)).

Evaluation of transcutol as a clonazepam transdermal permeation enhancer from hydrophilic gel formulations

The influence of diethyleneglycol monoethyl ether (transcutol), alone or in combination with propylene glycol, on clonazepam permeation through an artificial membrane and excised rabbit ear skin from Carbopol hydrogels was investigated. Drug kinetic permeation parameters were determined for both series of experiments and compared. Rheological characteristics, drug solubility and membrane/vehicle partition coefficient for each gel formulation were also determined, and their role in the formulation performance was investigated. Both series of experiments showed an increase of drug permeation as a function of transcutol content in the formulation. The combination of transcutol and propylene glycol resulted in a synergistic enhancement of clonazepam flux. A different trend was found in experiments with gels containing mixtures of the two enhancers, where an increase (in the case of artificial membrane) or a decrease (in the case of rabbit ear skin) of drug permeation was found by increasing the transcutol/propylene glycol ratio in the mixture. Such a result is explained on the basis of the particular mechanism of action demonstrated for transcutol which associates the increase of drug solubility to the potent effect of a depot in the skin.

Diclofenac metabolic profile following in vitro percutaneous absorption through viable human skin

The extent of metabolism of diclofenac sodium in excised viable human skin was investigated using combination HPLC and radioactivity assay. In an earlier diffusion experiment using an in vitro flow-through diffusion system, radiolabelled diclofenac sodium in either lotion (Pennsaid) or aqueous solution was applied to viable human skin, either as single dose or multiple dose (8 times over 2 days). In this study, the receptor fluid samples from the diffusion experiment were subjected to extraction and the aliquot was analysed using HPLC to separate diclofenac and authentic metabolites. Based on the radioactivity of each HPLC fraction, the collection time of the fractions was compared with the retention time of diclofenac and metabolites in standard solutions. The samples from a single or multiple dose application of lotion showed radioactivity in mainly one fraction, whose retention time corresponded with diclofenac. Other HPLC fractions showed none or only small amounts of radioactivity within the error range of the assay. The same results were obtained with the pooled samples from the application of the lotion or of aqueous solution. The results suggest that diclofenac sodium does not undergo metabolism in viable human epidermis during percutaneous absorption in vitro. Hence, with topical application to human skin in vivo, diclofenac will be delivered with minimal, if any, metabolism.

In vitro study of transdermal nicotine delivery: influence of rate-controlling membranes and adhesives

The objective of this study was to evaluate the influence of a rate-controlling membrane and adhesive on the in vitro permeation of nicotine. The physicochemical properties of the adhesive, including adhesion and rheology (viscosity), were also detected. Higher permeability of nicotine was observed through a hydrophilic membrane than through a hydrophobic membrane. Natural rubber and silicone were used as the adhesive bases, respectively. The silicone adhesive showed the highest adhesion among all adhesive formulations. To increase the adhesion of natural rubber, a tackifier (polyisoprene) and a secondary tackifier (terpene polymer; Px 1150) were incorporated into the formulations to achieve acceptable adhesion. The nicotine permeation through silicone adhesive and three natural rubber adhesives with the secondary tackifier (2%, 4%, and 6% Px 1150) was close to that from a commercially available patch (Habitrol), although the loading amount of nicotine was not the same. A longer lag time during the in vitro permeation study of nicotine was required for the adhesives prepared in our laboratory than for the commercially available patch.

Transdermal iontophoretic delivery of diclofenac sodium from various polymer formulations: in vitro and in vivo studies

The objective of this study was to evaluate the in vitro and in vivo transdermal iontophoresis of various diclofenac sodium polymer formulations. The excised rat skin, human skin as well as cellulose membrane were used to examine the in vitro drug permeation whereas the microdialysis technique was used to monitor the drug concentration in vivo. Polymer solutions based on polyvinylpyrrolidone (PVP) and hydroxypropyl methylcellulose (HPMC) binary system showed higher drug permeability than that of single polymer vehicle. The effect of formulations on drug permeation through cellulose membrane was quite different from those through rat skin and human skin, which can be explained by the different permeation pathways between them. It appeared to be a membrane-controlled mechanism but not the vehicle matrix-controlled mechanism for diclofenac hydrogels when using skin as the diffusion barrier. The recovery of diclofenac sodium in the in vivo microdialysis was approximately 80-90%, indicating this technique can be used in the intradermal drug monitoring. For all the polymer formulations tested, there was a good relationship between the in vitro and in vivo drug permeation. A synergistic effect on drug permeation was observed when transdermal iontophoresis combined with the pretreatment of cardamom oil as a permeation enhancer.

Influence of propylene glycol and isopropyl myristate on the in vitro percutaneous penetration of diclofenac sodium from carbopol gels

The influence of propylene glycol (PG) on the in vitro penetration of diclofenac sodium (DFS) through a synthetic membrane and abdominal rat skin from carbopol gels was investigated using Franz-type diffusion cells. The combined effect of isopropyl myristate (IPM) and PG was also evaluated. It was found that the penetration through the synthetic membrane was well described by the Higuchi model. The gel containing 40% PG showed the highest release rate, indicating that a releasing maximum exists for PG content which provides the fully solubilized drug in the vehicle. When using rat skin as the barrier, the penetration rate was controlled by the membrane. DFS flux decreased with increasing PG content of the gels due to an increase of the drug affinity to the vehicle. A cosolvent action of PG was evident. However, the combination of PG and IPM resulted in a synergistic enhancement of DFS flux. Maximum enhancing activity was obtained from gels containing 40% PG, which yielded an enhancement ratio of about 8. Increasing IPM content from 3 to 5% increased the flux and decreased the lag time taken to reach a steady-state level.

In vivo bioavailability and metabolism of topical diclofenac lotion in human volunteers

PURPOSE

The primary objective of this study was to determine the rate and extent of transdermal absorption for systemic delivery of diclofenac from Pennsaid (Dimethaid Research, Inc.) topical lotion into the systemic circulation after the lotion was applied to human volunteers, in an open treatment, non-blinded, non-vehicle controlled study. In addition, the in vivo metabolism of this topical diclofenac lotion has also been studied.

METHODS

Human volunteers were dosed with topical [14C]-diclofenac sodium 1.5% lotion on the knee for 24 h. Sequential time blood and urine samples were taken to determine pharmacokinetics, bioavailability and metabolism.

RESULTS

Topical absorption was 6.6% of applied dose. Peak plasma 14C occurred at 30 h after dosing, and peak urinary 14C excretion was at 24-48 h. The urinary 14C excretion pattern exhibits more elimination towards 24 h and beyond, as opposed to early urinary 14C excretion. This suggests a continuous delivery of [14C]-diclofenac sodium from the lotion into and through skin which only ceased when the dosing site was washed. Skin surface residue at 24 h was 26 +/- 9.5% dose (remainder assumed lost to clothing and bedding). Extraction of metabolites from urine amounted to 7.4-22.7% in untreated urine, suggesting substantial diclofenac metabolism to more water soluble metabolites, probably conjugates, which could not be extracted by the method employed. Two Dimensional TLC analysis of untreated urine showed minimal or no diclofenac, again emphasizing the extensive in vivo metabolism of this drug. Treatment of the same urine samples with the enzymes sulfatase and beta-glucuronidase showed a substantial increase in the extractable material. Three spots were consistently present in each sample run, namely diclofenac, 3'hydroxy diclofenac and an intermediate polar metabolite (probably a hydroxylated metabolite). Therefore, there was significant sulfation and glucuronidation of both diclofenac and numerous hydroxy metabolites of diclofenac, but many of the metabolites/conjugates remain unidentified. CONCLUSIONS; There was a continuous delivery of diclofenac sodium from the lotion into and through the skin, which ceased after the dosing site was washed. The majority of the material excreted in the urine were conjugates of hydroxylated metabolites, and not the parent chemical, although further identification is required.

In vitro cutaneous disposition of a topical diclofenac lotion in human skin: effect of a multi-dose regimen

PURPOSE

This study determines comparative bioavailability of diclofenac sodium lotion compared to an aqueous solution after topical application to viable human skin in vitro. In addition, the difference between a single dose and multiple doses (8 times) was also determined.

METHODS

An in vitro flow-through diffusion cell system was employed, using radiolabelled diclofenac sodium.

RESULTS

Multiple doses of lotion (2 microl/cm2 and 5 microl/cm2) delivered a total of 40.1 +/- 17.6 microg and 85.6 micro 41.4 microg diclofenac, respectively, at 48 h, compared to only 9.4 +/- 2.9 microg and 35.7 +/- 19.0 microg absorbed after topical application of diclofenac as an aqueous solution (P < 0.05). A single dose study showed no statistical difference between diclofenac delivered in lotion or an aqueous solution. Over 48 h the total absorption from lotion was 10.2 +/- 6.7 microg and 26.2 +/- 17.6 microg (2 microl/cm2 and 5 microl/cm2, respectively), compared to 8.3 +/- 1.5 microg and 12.5 +/- 5.7 microg from an aqueous solution. Both single doses of lotion and aqueous diclofenac showed decreased diclofenac absorption into the receptor fluid between 12 and 24 h. However, when applied multiple times, absorption from lotion was continually increasing up to 48 h. The total dose accountability ranged from 76.8 +/- 8.2% to 110.6 +/- 15. 1% of the applied dose.

CONCLUSIONS

Diclofenac lotion exhibited enhanced diclofenac percutaneous absorption rate through human skin (mass, flux and partition coefficient) when applied a multiple number of times and this enhanced absorption was maintained over 48 h. This suggests that a constituent of the lotion (DMSO) will enhance human skin absorption of diclofenac when used in a multi-dose regimen, but not after a single dose.