Validation protocol of an automated in-line flow-through diffusion equipment for in vitro permeation studies

Evaluation of in vitro Skin Permeation of Clascoterone From Clascoterone Topical Cream, 1% (w/w)

Winlevi® (clascoterone) topical cream (1%, w/w) was approved by the U.S. FDA for the treatment of acne vulgaris in patients 12 years of age and older. The active ingredient, clascoterone, is not stable in physiological solutions and can hydrolyze to cortexolone at body temperature. Instability of clascoterone poses a significant challenge in accurately assessing the rate and extent of clascoterone permeation in vitro. Therefore, the purpose of this study was to develop an in vitro skin permeation test (IVPT) method, and a robust analytical method, that can minimize hydrolyzation of clascoterone during the study for quantification of clascoterone. Two IVPT methods, using either vertical diffusion cells or flow-through cells, were developed and compared to evaluate in vitro permeation of clascoterone from Winlevi. A liquid chromatography with tandem mass spectrometry (LC-MS/MS) method was developed to monitor the level of clascoterone and cortexolone in the IVPT samples. The analytical method features a 2-min high-throughput analysis with good linearity, selectivity, and showed a lower limit of quantitation (LLOQ) of 0.5 ng/mL for both clascoterone and cortexolone. The in vitro skin permeation of clascoterone and cortexolone was observed as early as 2 h in both IVPT methods. A substantive amount of clascoterone was found to hydrolyze to cortexolone when using the vertical static diffusion cells with aliquot sampling. Conversely, degradation of clascoterone was significantly minimized when using the flow-through diffusion cells with fractional sampling. The data enhanced our understanding of in vitro permeation of clascoterone following topical application of the Winlevi topical cream, 1% and underscores the importance of IVPT method development and optimization during product development.

In Vitro Human Dermal Absorption Studies on Pesticides in Complex Mixtures: Investigation of Guidance Criteria and Possible Impact Parameters

Pesticides must not pose unacceptable risks to human health, so risk assessments are conducted before products are authorised. Dermal exposure is often the main route of intake, so estimating realistic and trustworthy dermal absorption values is crucial for risk assessment. Although there are agreed test guidelines for in vitro dermal absorption studies, not every product is tested due to cost reasons. The present dataset consists of 945 individual in vitro experiments on the dermal absorption of human skin with 179 active substances of pesticides in 353 different mixtures, including concentrates and dilutions. The dataset was evaluated to identify the possible impacts of experimental conditions and physico-chemical properties on dermal absorption. The dataset was also analysed to assess the appropriateness of the pro rata correction for untested dilutions, and the set concentration cut-off to decide on the dilution status for choosing a default value on dermal absorption. The study found that the implementation of specific guidelines improved the harmonisation of study conduct, with support for approaches such as pro rata correction and default values. Further analysis of the specific co-formulants may identify influencing factors that may be more important than the experimental variables.

Skin-on-a-Chip Technology for Testing Transdermal Drug Delivery-Starting Points and Recent Developments

During the last decades, several technologies were developed for testing drug delivery through the dermal barrier. Investigation of drug penetration across the skin can be important in topical pharmaceutical formulations and also in cosmeto-science. The state-of- the-art in the field of skin diffusion measurements, different devices, and diffusion platforms used, are summarized in the introductory part of this review. Then the methodologies applied at Pázmány Péter Catholic University are shown in detail. The main testing platforms (Franz diffusion cells, skin-on-a-chip devices) and the major scientific projects (P-glycoprotein interaction in the skin; new skin equivalents for diffusion purposes) are also presented in one section. The main achievements of our research are briefly summarized: (1) new skin-on-a-chip microfluidic devices were validated as tools for drug penetration studies for the skin; (2) P-glycoprotein transport has an absorptive orientation in the skin; (3) skin samples cannot be used for transporter interaction studies after freezing and thawing; (4) penetration of hydrophilic model drugs is lower in aged than in young skin; (5) mechanical sensitization is needed for excised rodent and pig skins for drug absorption measurements. Our validated skin-on-a-chip platform is available for other research groups to use for testing and for utilizing it for different purposes.

The Development of an In Vitro Horizontal Diffusion Cell to Monitor Nasal Powder Penetration Inline

The development of in vitro investigation models could be important using sensitive and fast methods during formulation. Intranasal applied drugs (meloxicam, lamotrigine, and levodopa) avoid the gastrointestinal tract and can achieve higher bioavailability, therefore a penetration extent is a key property. In this study, the in vitro adaptability of a modified horizontal diffusion cell was tested by using these model active pharmaceutical ingredients (APIs). The special factors consisted of the volume of the chambers, the arrangement of the stirrers, the design of probe input for real-time analysis and decreased membrane area. Membranes were impregnated by isopropyl myristate and by using phosphate buffer to evaluate the effect of API hydrophilicity on the diffusion properties. The lipophilicity of the API was proportional to the penetration extent through isopropyl myristate-impregnated membranes compared with buffer-soaked membranes. After evaluating the arithmetic mean of standard relative deviations and the penetrated extent of APIs at 15 min, Metricel^® could be suggested for levodopa and meloxicam, and Whatman™ for lamotrigine. The modified model is suitable for inline, real-time detection, at nasal conditions, using small volumes of phases, impregnated membrane, to monitor the diffusion of the drug and to determine its concentration in the acceptor and donor phases.

Cutaneous Pharmacokinetics of Acyclovir Cream 5% Products: Evaluating Bioequivalence with an In Vitro Permeation Test and an Adaptation of Scaled Average Bioequivalence

PURPOSE

The in vitro permeation test (IVPT) with a new statistical approach was investigated to evaluate the utility of an IVPT methodology as a sensitive tool to support a demonstration of bioequivalence (BE) for topical dermatological drug products.

METHODS

IVPT experiments were performed utilizing ex vivo human skin. The initial screening tests involved four differently formulated acyclovir 5% creams: the U.S. Zovirax® as the reference product and the U.K. Zovirax®, Aciclovir 1A Pharma® and Aciclostad® as test products. Subsequently, a pivotal BE study was conducted comparing the two Zovirax® creams. The resulting data was used to evaluate BE of test (T) versus reference (R), T versus T, and R versus R, with an adaption of scaled average BE approach to address high variability in IVPT data.

RESULTS

More acyclovir permeated into and through the skin from the two Zovirax® creams compared to the two non-Zovirax® creams. The U.S. Zovirax® cream showed a significantly higher J_max and total amount permeated over 48 h, compared to the U.K. Zovirax® cream. The statistical analysis indicated that the test and reference products were not bioequivalent, whereas each product tested against itself was shown to be bioequivalent.

CONCLUSIONS

The current study demonstrated that the IVPT method, with an appropriate statistical analysis of the results, is a sensitive and discriminating test that can detect differences in the rate and extent of acyclovir bioavailability in the skin from differently formulated cream products.

The influence of diffusion cell type and experimental temperature on machine learning models of skin permeability

OBJECTIVES

The aim of this study was to use Gaussian process regression (GPR) methods to quantify the effect of experimental temperature (T_exp ) and choice of diffusion cell on model quality and performance.

METHODS

Data were collated from the literature. Static and flow-through diffusion cell data were separated, and a series of GPR experiments was conducted. The effect of T_exp was assessed by comparing a range of datasets where T_exp either remained constant or was varied from 22 to 45 °C.

KEY FINDINGS

Using data from flow-through diffusion cells results in poor model performance. Data from static diffusion cells resulted in significantly greater performance. Inclusion of data from flow-through cell experiments reduces overall model quality. Consideration of T_exp improves model quality when the dataset used exhibits a wide range of experimental temperatures.

CONCLUSIONS

This study highlights the problem of collating literature data into datasets from which models are constructed without consideration of the nature of those data. In order to optimise model quality data from only static, Franz-type, experiments should be used to construct the model and T_exp should either be incorporated as a descriptor in the model if data are collated from a range of studies conducted at different temperatures.

Clotrimazole Loaded Ufosomes for Topical Delivery: Formulation Development and In-Vitro Studies

Global incidence of superficial fungal infections caused by dermatophytes is high and affects around 40 million people. It is the fourth most common cause of infection. Clotrimazole, a broad spectrum imidazole antifungal agent is widely used to treat fungal infections. Conventional topical formulations of clotrimazole are intended to treat infections by effective penetration of drugs into the stratum corneum. However, drawbacks such as poor dermal bioavailability, poor penetration, and variable drug levels limit the efficiency. The present study aims to load clotrimazole into ufosomes and evaluate its topical bioavailability. Clotrimazole loaded ufosomes were prepared using cholesterol and sodium oleate by thin film hydration technique and evaluated for size, polydispersity index, and entrapment efficiency to obtain optimized formulation. Optimized formulation was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). Skin diffusion studies and tape-stripping were performed using human skin to determine the amount of clotrimazole accumulated in different layers of the skin. Results showed that the optimized formulation had vesicle size <250 nm with ~84% entrapment efficiency. XRD and DSC confirmed the entrapment of clotrimazole into ufosomes. No permeation was observed through the skin up to 24 h following the permeation studies. Tape-stripping revealed that ufosomes led to accumulation of more clotrimazole in the skin compared to marketed formulation (Perrigo). Overall, results revealed the capability of ufosomes in improving the skin bioavailability of clotrimazole.

Transungual Delivery of Ciclopirox Is Increased 3⁻4-Fold by Mechanical Fenestration of Human Nail Plate in an In Vitro Model

Onychomycosis is a fungal infection of nails that is widespread and difficult to treat because of the impermeable nature of human nails. Topically applied anti-fungal agents cannot penetrate this structure, and treatment regimens often resort to systemic antifungals with concomitant side effects. One recent clinical study suggested that mechanical fenestration of the nail using an intelligent nail drill might be a possible solution to this problem. In this work, an in vitro model of the transungual delivery of antifungal agents is presented, which utilizes real nail tissue and an inline flow system. This system was deployed to measure transungual delivery of ciclopirox and determined that nail fenestration improved drug delivery by 3–4-fold after 42 days. This study bolsters the argument that nail fenestration should be accepted as a pretreatment for onychomycosis and offers a way of evaluating new drugs or formulations designed to combat this condition.

Design, Development, and Characterization of Imiquimod-Loaded Chitosan Films for Topical Delivery

Aldara™ (5% w/w imiquimod) topical cream is approved by the US FDA for the treatment of superficial basal cell carcinoma. However, the cream formulation suffers from dose variability, low drug availability due to the incomplete release, and poor patient compliance. To achieve sustained and complete release of imiquimod, chitosan films were prepared by casting using propylene glycol as a plasticizer. Chitosan films had appropriate physicochemical characteristics for wound dressing and excellent content uniformity and maintained the original physical form of imiquimod. Films were capable of releasing a defined dose of imiquimod over a period of 7 days. The bioactivity of imiquimod was not affected by its entrapment in chitosan matrix as indicated by the results of in vitro growth inhibition assay. In addition, the film formulation showed significantly (p ˂ 0.05) higher drug accumulation in the skin when compared to commercial cream formulation.

Multi-chamber microfluidic platform for high-precision skin permeation testing

The established in vitro tool used for testing the absorption and penetration of chemicals through skin in pharmacology, toxicology and cosmetic science is the static Franz diffusion cell. While widespread, Franz cells are relatively costly, low-throughput and results may suffer from poor reproducibility. Microfluidics has the potential to overcome these drawbacks. In this paper, we present a novel microfluidic skin permeation platform and validate it rigorously against the Franz cell by comparing the transport of 3 model chemicals of varying lipophilicity: caffeine, salicylic acid and testosterone. Permeation experiments through silicone membranes show that the chip yields higher sensitivity in permeant cumulative amounts and comparable or lower coefficients of variation. Using a skin organotypic culture, we show that the chip decreases the effect of unstirred water layers that can occur in static Franz cells. The validation reported herein sets the stage for efficient skin permeation and toxicity screening and further development of microfluidic skin-on-chip devices.

In vitro human skin penetration model for organophosphorus compounds with different physicochemical properties

A flow-through diffusion cell was validated for in vitro human epidermal penetration studies of organophosphorus compounds (OPCs) applied by infinite dosing. By testing OPCs with similar molecular weight but different physicochemical properties, it was shown that hydrophilic and lipophilic properties are major determinants for the penetration rate. Lipophilic OPCs displayed maximum cumulative penetration in the 20-75% agent concentration range whereas the hydrophilic OPCs displayed maximum cumulative penetration at 10 or 20% agent concentration. Low penetration was observed for all agents at 1% agent concentration or when applied as neat agents. The impact of the receptor solution composition was evaluated by comparing the penetration using receptor solutions of different ratios of ethanol and water. For diluted OPCs, a high concentration of ethanol in the receptor solution significantly increased the penetration compared to lower concentrations. When OPCs were applied as neat agents, the composition of the receptor solution only affected the penetration for one of four tested compounds. In conclusion, the flow-through diffusion cell was useful for examining the penetration of OPCs through the epidermal membrane. It was also demonstrated that the penetration rates of OPCs are strongly influenced by dilution in water and the receptor fluid composition.

In vitro-in vivo correlation for complex non-oral drug products: Where do we stand?

In vitro–in vivo correlation (IVIVC) is a predictive mathematical model describing the relationship between an in vitro property and a relevant in vivo response of drug products. Since the U.S. Food and Drug Administration (FDA) published a regulatory guidance on the development, evaluation, and applications of IVIVC for extended release (ER) oral dosage forms in 1997, IVIVC has been one of the most important issues in the field of pharmaceutics. However, even with the aid of the FDA IVIVC Guidance, only very limited Abbreviated New Drug Application (ANDA) submission for ER oral drug products included adequate IVIVC data to enable the completion of bioequivalence (BE) review within first review cycle. Establishing an IVIVC for non-oral dosage forms has remained extremely challenging due to their complex nature and the lack of in vitro release methods that are capable of mimicking in vivo drug release conditions. This review presents a general overview of recent advances in the development of IVIVC for complex non-oral dosage forms (such as parenteral polymeric microspheres/implants, and transdermal formulations), and briefly summarizes the knowledge gained over the past two decades. Lastly this review discusses possible directions for future development of IVIVC for complex non-oral dosage forms.

Physical Stability Studies of Semi-Solid Formulations from Natural Compounds Loaded with Chitosan Microspheres

A chitosan-based hydrophilic system containing an olive leaf extract was designed and its antioxidant capacity was evaluated. Encapsulation of olive leaf extract in chitosan microspheres was carried out by a spray-drying process. The particles obtained with this technique were found to be spherical and had a positive surface charge, which is an indicator of mucoadhesiveness. FTIR and X-ray diffraction results showed that there are not specific interactions of polyphenolic compounds in olive leaf extract with the chitosan matrix. Stability and release studies of chitosan microspheres loaded with olive leaf extract before and after the incorporation into a moisturizer base were performed. The resulting data showed that the developed formulations were stable up to three months. The encapsulation efficiency was around 44% and the release properties of polyphenols from the microspheres were found to be pH dependent. At pH 7.4, polyphenols release was complete after 6 h; whereas the amount of polyphenols released was 40% after the same time at pH 5.5.

Advances in the bioanalytical study of drug delivery across the skin

The study of a drug's dermal penetration profile provides important pharmaceutical data for the rational development of topical and transdermal delivery systems because the skin is a broadly used delivery route for local and systemic drugs and a potential route for gene therapy and vaccines. Monitoring drug penetration across the skin and quantifying its levels in different skin layers have been constant challenges due to the detection limitations of the available techniques, as well as the inherent interference in this tissue. This review explores and discusses several bionalytical methods that are indispensable tools to study drugs across the skin. In addressing the main topic, we structure the review highlighting the skin as an important route of drug administration and its structure, skin membrane models most used and its properties, in vitro and in vivo assays most used in the study of drug delivery to the skin, the techniques for processing the skin for subsequent analysis by bioanalytical methods that have a theoretical and practical approach showing its applicability, limitations and also including examples of its use. This review has a comprehensive approach in order to help researchers design their experiments and update the applicability and advances in this area of expertise.

Polihexanide solution is more efficient than alcohol to remove phenol in chemical matricectomy: an in vitro study

For treatment of ingrown toenails, a phenolization approach is often chosen. Many reports describe a lavage of the wound with alcohol to neutralize any residual phenol; however, it remains uncertain if there is a more effective solution for use in the lavage step. The aim of our study was to analyze the suitability and effectiveness of 0.1% polihexanide solution compared with isopropyl alcohol in the removal of excess phenol after treatment for ingrown toenails. We performed an in vitro study using human matrix and a diffusion cell apparatus to measure the amount of phenol remaining after two lavage washes. The effect of phenol evaporation was also examined.When phenol was irrigated with alcohol alone, 27.43 ± 4.10 mg (57.74%) of the initial amount of phenol was recovered. If irrigated with 0.1% polihexanide, 35.98 ± 2.93 mg (75.74%) of phenol was recovered. These results indicate that a polihexanide lavage step has significantly higher efficiency for removing excess phenol relative to alcohol.

Alcohol plus chlorhexidine is more efficient than alcohol alone for phenol-based chemical matricectomy: an in vitro study

BACKGROUND

A phenolization approach is often chosen for treatment of ingrown toenails. Many reports describe lavage of the wound with alcohol to neutralize any residual phenol. The aim of our study was to compare the suitability and effectiveness of a solution consisting of alcohol plus chlorhexidine with that of alcohol alone in a lavage step during the treatment of ingrown toenails using a phenolization procedure.

METHODS

We performed an in vitro study using human matrix and a diffusion cell apparatus to measure the amount of phenol remaining after various lavage washes. The effect of phenol evaporation was also examined.

RESULTS

When phenol was irrigated with alcohol alone, total phenol recovered was 29.9 ± 4.8 mg (62.9% of the initial amount). When the phenol was irrigated with isopropyl alcohol plus 0.5% chlorhexidine, 39.8 ± 1.7 mg (83.8%) of phenol was recovered.

CONCLUSION

A lavage step including alcohol and chlorhexidine is more effective than alcohol alone for removal of excess phenol. The addition of chlorhexidine also contributed to inhibition of the action of phenol. This approach provides a suitable and effective means of diluting and removing any excess or residual phenol from the exposed area.

A miniaturized flow-through cell to evaluate skin permeation of endoxifen

Endoxifen, an anti-estrogenic agent, has been recently implicated in the use of breast cancer. Its physicochemical properties make it a good candidate for transdermal delivery. However, as an investigative drug, its limited supply makes it difficult to conduct extensive pre-formulation studies. To address this issue, a miniaturized flow-through diffusion cell has been fabricated that utilized minimal amounts of the drug for in vitro skin permeation studies. The novel flow-through cells have been validated against horizontal diffusion cells and shown to cause no noticeable damage to the applied skin, as observed by histological sectioning. The cells were also demonstrated to be useful in search of suitable enhancers for endoxifen. Endoxifen permeation using permeation enhancers was tested by using this new device and limonene was found to achieve highest flux, attaining the requirement for clinical applications. The fabricated cells can thus be useful in carrying out pre-formulation studies for expensive, new drug entities, both in industrial as well as academic research.

Enhanced removal of phenol with saline solution over alcohol: an in vitro study

BACKGROUND

Phenol cauterization is a chemical equivalent often chosen for treatment of ingrown toenails. Many reports describe intraoperative irrigation, or lavage, of the wound with various types of alcohol to neutralize any remaining phenol. There are conflicting reports in the literature as to whether true neutralization or merely effective removal of excess phenol is needed.

OBJECTIVE

The aim of our study was to analyze the suitability and effectiveness of ethyl alcohol versus sterile saline when used in a lavage step after phenol application in the treatment of ingrown toenails.

METHODS

We performed an in vitro study using human skin and a diffusion cell apparatus to measure the amount of phenol recovered after lavage with ethyl alcohol or sterile saline.

RESULTS

When the wound was irrigated with ethyl alcohol, the total phenol recovered after two irrigation washes was 55.7% of the original amount initially used in treatment, compared with 80.4% when sterile saline solution was used for irrigation.

CONCLUSION

Alcohol and sterile saline solution do not neutralize phenol but dilute it and aid in its removal. We found that saline solution recovered more phenol than when washing with alcohol and recommend its use instead of alcohol for irrigation purposes after chemical matrixectomy.

Elastic vesicles of sumatriptan succinate for transdermal administration: characterization and in vitro permeation studies

Elastic liposomes, including sumatriptan succinate, were prepared for their transdermal administration. Lipid vesicles containing 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) or l-α-phosphatidylcholine dilauroyl (DLPC) phospholipids were characterized for various parameters, including size, particle-size distribution (i.e., polydispersity index), and elasticity. In vitro transdermal experiments for the study of the skin penetration of sumatriptan succinate contained in liposomes were performed by using flow-through diffusion cells. The diameter of sumatriptan liposomes with different lipid compositions varied between 279 and 282 nm, and the polydispersity index value for the size distribution of liposomal formulations was <0.5. DLPC vesicles proved to be more elastic and provided a higher sumatriptan transdermal flux than vesicles formulated with DOPC phospolipid.

Permeation of four oral drugs through human intestinal mucosa

The pharmaceutical industry is in need of rapid and accurate methods to screen new drug leads for intestinal permeability potential in the early stages of drug discovery. Excised human jejunal mucosa was used to investigate the permeability of the small intestine to four oral drugs, using a flow-through diffusion system. The four drugs were selected as representative model compounds of drug classes 1 and 3 according to the biopharmaceutics classification system (BCS). The drugs selected were zidovudine, propranolol HCl, didanosine, and enalapril maleate. Permeability values from our in vitro diffusion model were compared with the BCS permeability classification and in vivo and in vitro gastrointestinal drug permeability. The flux rates of the four drugs were influenced by the length of the experiment. Both class 1 drugs showed a significantly higher mean flux rate between 2 and 6 h across the jejunal mucosa compared to the class 3 drugs. The results are therefore in line with the drugs' BCS classification. The results of this study show that the permeability values of jejunal mucosa obtained with the flow-through diffusion system are good predictors of the selected BCS class 1 and 3 drugs' permeation, and it concurred with other in vitro and in vivo studies.

In vitro Skin Permeability of Different Terbinafine Hydrochloride Formulations

The objectives of the study are to determine the in vitro permeability of different terbinafine hydrochloride formulations through human skin and to measure the respective concentrations of each formulation within the exposed skin tissue. The permeation of three commercially available 1% terbinafine hydrochloride formulations and two terbinafine hydrochloride solutions of 10 and 20 mg/ml through human skin was investigated using an in vitro continuous flow-through perfusion system. The terbinafine hydrochloride retained in the skin was extracted and analysed. The terbinafine hydrochloride from the different formulations readily diffused into the skin tissue. However, no flux values for any of the terbinafine hydrochloride formulations through the skin into the receptor fluid were found. The mean terbinafine hydrochloride concentrations in the skin after 24 h exposure to the three commercial formulations were 3.589, 1.590 and 4.219 μg/ml respectively. The mean terbinafine hydrochloride concentrations in the skin after 24 h of exposure to the terbinafine hydrochloride solutions (PBS/Methanol 1:1) of 10 and 20 mg/ml were 85.280 and 154.680 μg/ml respectively. The mean terbinafine hydrochloride concentration in the skin exposed to the 10 mg/ml PBS/Methanol solution was higher than those from the three commercial formulations. Terbinafine seems to accumulate in skin/bind to the skin, rather than to diffuse through the skin into the receptor compartment. This unique pharmacokinetic property of terbinafine hydrochloride may enhance its efficacy as topical antifungal and reduce systemic side effects.

Parallel Artificial Membrane Permeability Assay: A New Membrane for the Fast Prediction of Passive Human Skin Permeability

This work was devoted to the search for new artificial membranes allowing a rapid evaluation of passive human skin permeation of compounds with a parallel artificial membrane permeability assay (PAMPA). Effective permeability coefficients (Pe) determined for a set of compounds using the PAMPA technique with isopropyl myristate (IPM) and silicone oil, alone or in mixture, were compared to the corresponding human skin permeability coefficient values (Kp). A good correlation between Pe and Kp was found for compounds tested through a membrane consisting of 70% silicone and 30% IPM. Moreover, positive correlation between the membrane retention of compounds and stratum corneum/water partition coefficients (PSC) was established. These results showed that this new artificial membrane, defined as PAMPA-skin, is able to mimic the main barrier properties of human stratum corneum and can be used for the fast prediction of passive human skin permeability coefficients.

Current status and future potential of transdermal drug delivery

The past twenty five years have seen an explosion in the creation and discovery of new medicinal agents. Related innovations in drug delivery systems have not only enabled the successful implementation of many of these novel pharmaceuticals, but have also permitted the development of new medical treatments with existing drugs. The creation of transdermal delivery systems has been one of the most important of these innovations, offering a number of advantages over the oral route. In this article, we discuss the already significant impact this field has made on the administration of various pharmaceuticals; explore limitations of the current technology; and discuss methods under exploration for overcoming these limitations and the challenges ahead.

Terpenes in ethanol: haloperidol permeation and partition through human skin and stratum corneum changes

Carvacrol, linalool and alpha-terpineol (5% w/v) in 50% ethanol were used to enhance the permeation of haloperidol (HP) through human skin in vitro and their enhancement mechanism was investigated with HP-stratum corneum (SC) binding studies, fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). Carvacrol followed by terpineol and linalool enhanced flux and permeability coefficient but only carvacrol provided the required plasma concentration and the permeated daily doses. All terpenes increased the activity coefficient of HP in the skin. Carvacrol increased the lag time, which could be due to slow redistribution within SC. The thermogram of hydrated SC showed two lipid endotherms T1 and T2 at 65 and 78 degrees C and protein endotherm T3 at 97 degrees C. All endotherms were absent after SC treated for 48 h with 12 ml of terpene solutions and a decrease in melting points (m.p.) of lipids with a shift of protein endotherm were observed after 12 h treatment with 7 ml of terpene solutions. Linalool and terpineol decreased the m.p. of T1 to 33 degrees C. Carvacrol increased the T1 peak area, which was attributed to lateral lipid bilayer swelling. The IR spectra showed decreases in peak areas and heights of CH2 stretchings but did not show shift of these peaks, increase in their peak widths and shift in amide bands. All the three terpenes disrupted the lipid bilayer and extracted the lipids. Moreover, carvacrol increased the partition of HP whilst linalool and terpineol fluidized the lipids at skin temperature. There could be other possible protein-terpene interactions.