A transdermal review on permeation of drug formulations, modifier compounds and delivery methods

Thermosensitive biomaterial gels with chemical permeation enhancers for enhanced microneedle delivery of naltrexone for managing opioid and alcohol dependency

Naltrexone (NTX) can be transdermally delivered using microneedles (MN) to treat opioid and alcohol misuse disorders, but delivery is blunted by rapid in vivo micropore closure. Poloxamer (P407), a thermosensitive biocompatible hydrogel, sustains NTX delivery through MN-treated skin by generating a drug depot within the micropores. Optimizing P407 formulations could maintain sustained delivery after micropore closure while reducing required patch sizes, which would be more discreet and preferred by most patients. Here we developed NTX-loaded P407 gels with chemical permeation enhancers (CPEs) and used these novel formulations alongside MN treatment to enhance NTX permeation, utilizing parallel micropore and intact skin transport pathways. We analyzed physicochemical and rheological properties of CPE-loaded P407 formulations and selected formulations with DMSO and benzyl alcohol for further study. In vitro permeation tests demonstrated more consistent and sustained NTX delivery through MN-treated porcine skin from 16% P407 formulations vs. aqueous solutions. P407 with 1% benzyl alcohol and 10% DMSO significantly, P < 0.05, increased flux through MN-treated skin vs. formulations with benzyl alcohol alone. This formulation would require a smaller size patch than previously used to deliver NTX in humans, with half the NTX concentration. This is the first time poloxamer biomaterials have been used in combination with CPEs to improve MN-assisted transdermal delivery of an opioid antagonist. Here we have demonstrated that P407 in combination with CPEs effectively sustains NTX delivery in MN-treated skin while requiring less NTX than previously needed to meet clinical goals.

The importance of metrological tools to implementation of alternative method OECD TG 428

Usually, if percutaneous absorption tests are conducted in accordance with OECD Guideline 428, in vitro determination is accepted by mainly regulatory agencies. In this paper, we focus on the lack of comparability of the results regarding the permeation parameter/flow rate, although it is widely discussed in the literature. This work sought to evaluate the absorption of caffeine using Franz-type diffusion cell with porcine ear skin samples, varying the storage duration and the way to handle them. Metrological tools were used for caffeine quantification such as certified reference material candidate, calibrated instruments, and validated methodology. Our results corroborate with the recommendation that membranes should be freshly prepared or frozen for short periods. Samples frozen for approximately one year should not be used because they present high cutaneous absorption. The results obtained for the absorption rate (J) are comparable to the results obtained by previous studies using similar experimental conditions. The evidence of the barrier characteristic promoted by the stratum corneum and the effect promoted by the storage time is shown through J = 6.25 ± 0.48 μg/cm²/h. We demonstrated the importance of metrological tools to guarantee reproducibility and comparability of the results between different laboratories.

Ascorbic acid encapsulated into negatively charged liposomes exhibits increased skin permeation, retention and enhances collagen synthesis by fibroblasts

Ascorbic acid (AA) is widely used in cosmetic formulations due to its antioxidant property and ability to increase collagen synthesis. Here, we encapsulated AA in vesicles with different lipid compositions. Negative liposome charge favored AA skin retention, with accumulation of 37 ± 12 and 74 ± 23 μg/cm² in the epidermis and dermis, respectively, after 6 hours. Drug flux was influenced by the formulation composition, and both the presence of cholesterol and the liposomes surface charge were able to increase the amount of AA crossing the skin. The formulation was stable for at least 30 days and promoted a 7-fold increase in flux compared to free AA. Additionally, liposomes were able to interact better with keratinocytes and fibroblasts membranes. In vitro efficacy studies demonstrated that associating AA to these liposomes resulted in increased effectiveness of type I collagen synthesis by fibroblasts and regeneration of UVA-induced damage in keratinocytes. Our results demonstrate the applicability of AA-negatively charged liposomes in promoting AA cutaneous permeation and increasing the retention and flux of this molecule in the skin. This formulation also increased AA stability and effectiveness, opening new perspectives for its application in view of reducing certain skin ageing outcomes.

Transdermal Delivery of Ibuprofen Utilizing a Novel Solvent-Free Pressure-sensitive Adhesive (PSA): TEPI® Technology

PURPOSE

The main objective of this present study was the investigation of potential novel transdermal patch technology (TEPI®) delivering ibuprofen as the active pharmaceutical ingredient (API) using a novel poly(ether-urethane)-silicone crosslinked pressure-sensitive adhesive (PSA) as the drug reservoir in a solvent-free manufacturing process.

METHODS

The patch was synthesized utilizing the hot-melt crosslinking technique without the addition of solvents at 80 °C in 100% relative humidity. Dissolution and permeation studies performed utilizing diffusion cells and subsequently HPLC validated methods were employed to determine the API content in the acceptor solution. Accelerated stability studies were also performed at 40 °C and 70% relative humidity. The adhesive performance of the fabricated patch was evaluated utilizing loop tack adhesion tests.

RESULTS

In vitro permeation experiments across both Strat-M® and human skin demonstrated that ibuprofen can easily be released from the adhesive matrix and penetrate through the studied membrane. A comparison on the permeation rates of the API across the two membranes indicated that there is not a strong correlation between the obtained data. The presence of chemical enhancers facilitated an increased flux of the API higher than observed in the basic formulation. Initial stability studies of the optimized formulation showed no degradation with respect to the drug content. Adhesion studies were also performed indicating higher values when compared with commercially available products.

CONCLUSIONS

The present study demonstrated the fabrication of an ibuprofen patch utilizing a versatile, solvent-free drug delivery platform. Upon optimization of the final system, the resulting patch offers many advantages compared to commercially available formulations including high drug loading (up to 25 wt%), good adhesion, and painless removal leaving no residues on the skin. This PSA offers many advantages over existing adhesive technology. Graphical Abstractᅟ.

Identifying present challenges to reliable future transdermal drug delivery products

Transdermal systems have become an accepted means of drug delivery, offering clinical benefits over other dosage forms. Although transdermal delivery has been very successful as a controlled release technology platform, there are a number of challenges that prevent this delivery route from achieving its fullest commercial potential. Additionally, beginning in 1997, transdermal drug delivery companies aligned with life science industries to deliver large molecules, peptides and proteins through the skin, which is difficult due to the skin barrier properties. A number of methods and technologies have been conceived to overcome the skin barrier. Among these are mechanical, chemical and thermal permeation enhancement techniques. These methods are briefly discussed as well as future directions for transdermal therapies.

Design and characterization of submicron formulation for a poorly soluble drug: the effect of Vitamin E TPGS and other solubilizers on skin permeability enhancement

In transdermal drug delivery systems (TDDS), it is a challenge to achieve stable and prolonged high permeation rates across the skin since the concentrations of the drug dissolved in the matrix have to be high in order to maintain zero order release kinetics. Several attempts have been reported to improve the permeability of poorly soluble drug compounds using supersaturated systems, however, due to thermodynamic challenges, there was a high tendency for the drug to nucleate immediately after formulating or even during storage. The present study focuses on the efficiency of drug crystals at the submicron/nano range in presence of different solubilizers to improve the permeation rate. Effect of several solubilizers, e.g. Pluronic F-127, Vitamin E TPGS, propylene glycol were studied on the submicron suspension systems of ibuprofen as a model drug. Various stabilizers such as hydroxylpropyl methylcellulose (HPMC) and polyvinylpyrrolidone (PVP) were examined to evaluate their crystal inhibitory effects on particle growth of the drug compound at submicron range. The overall permeation enhancement process through the skin seems to be influenced by the presence of solubilizers and also the presence of submicron drug crystal. The most promising stable formulation was developed with Vitamin E TPGS+HPMC submicron suspension, which produced higher permeation rate compared to other vehicles.

Pharmaceutical applications of cyclodextrins: effects on drug permeation through biological membranes

Objectives

Cyclodextrins are useful solubilizing excipients that have gained currency in the formulator's armamentarium based on their ability to temporarily camouflage undesirable physicochemical properties. In this context cyclodextrins can increase oral bioavailability, stabilize compounds to chemical and enzymatic degradation and can affect permeability through biological membranes under certain circumstances. This latter property is examined herein as a function of the published literature as well as work completed in our laboratories.

Key findings

Cyclodextrins can increase the uptake of drugs through biological barriers if the limiting barrier component is the unstirred water layer (UWL) that exists between the membrane and bulk water. This means that cyclodextrins are most useful when they interact with lipophiles in systems where such an UWL is present and contributes significantly to the barrier properties of the membrane. Furthermore, these principles are used to direct the optimal formulation of drugs in cyclodextrins. A second related critical success factor in the formulation of cyclodextrin-based drug product is an understanding of the kinetics and thermodynamics of complexation and the need to optimize the cyclodextrin amount and drug-to-cyclodextrin ratios. Drug formulations, especially those targeting compartments associated with limited dissolution (i.e. the eye, subcutaneous space, etc.), should be carefully designed such that the thermodynamic activity of the drug in the formulation is optimal meaning that there is sufficient cyclodextrin to solubilize the drug but not more than that. Increasing the cyclodextrin concentration decreases the formulation ‘push’ and may reduce the bioavailability of the system.

Conclusions

A mechanism-based understanding of cyclodextrin complexation is essential for the appropriate formulation of contemporary drug candidates.