Determining degree of saturation after application of transiently supersaturated metered dose aerosols for topical delivery of corticosteroids

The use of optical differential scanning calorimetry to investigate ibuprofen miscibility in polymeric films for topical drug delivery

Understanding drug miscibility in pharmaceutically relevant systems is essential for the development and optimisation of pharmaceutical dosage forms. This is particularly true for film forming systems which are designed to become supersaturated with drug, following application on the skin surface, whilst maintaining the physical stability of the drug for a suitable period to enhance drug delivery. For such formulations, chemical penetration enhancers as well as the drug are absorbed from the formulation into the skin, making understanding drug delivery from the films challenging. This study investigated the use of an optical differential scanning calorimetry (DSC) to understand drug miscibility in polymeric film forming systems and explain drug transport behaviour from film forming formulations, containing ibuprofen, a copolymer based on dimethylaminoethyl methacrylate, butyl methacrylate, and methyl methacrylate (Eudragit® E, EuE), a copolymer based on ethyl acrylate, methyl methacrylate and methacrylic acid ester with quaternary ammonium groups (Eudragit® RS, EuRS) and a copolymer based on methacrylic acid and methyl methacrylate (Eudragit® S, EuS), with and without the chemical penetration enhancer propylene glycol, across a model membrane. The optical DSC enabled the rapid screening of not only drug-polymer miscibility, but also drug-vehicle miscibility, while considering both the melting-point depression and melting enthalpy of the drug due to the presence of the polymer/polymer-based vehicle, obtained via thermal analysis by structural characterisation (TASC) and DSC analysis, respectively. The results obtained enable the polymers studied to be ranked in the order of EuE > EuRS > EuS, with EuE being more miscible with ibuprofen, and the incorporation of a penetration enhancer in the film forming system formulation was found to increase ibuprofen solubility in EuE- and EuRS- based films. The drug-polymer/vehicle miscibility information obtained via optical DSC provided understanding of drug transport from film forming systems with the higher miscibility of ibuprofen with EuE reducing drug transport through decreasing drug saturation in the film. The higher drug transport from films containing EuRS and EuS could also be linked to drug miscibility with the polymer and showed dependence on ibuprofen loading in the formulation. Overall optical DSC has been demonstrated to be a valuable tool for determining drug-vehicle miscibility for pharmaceutical product development.

Controlled Release Film Forming Systems in Drug Delivery: The Potential for Efficient Drug Delivery

Despite many available approaches for transdermal drug delivery, patient compliance and drug targeting at the desired concentration are still concerns for effective therapies. Precise and efficient film-forming systems provide great potential for controlling drug delivery through the skin with the combined advantages of films and hydrogels. The associated disadvantages of both systems (films and hydrogels) will be overcome in film-forming systems. Different strategies have been designed to control drug release through the skin, including changes to film-forming polymers, plasticizers, additives or even model drugs in formulations. In the current review, we aim to discuss the recent advances in film-forming systems to provide the principles and review the methods of these systems as applied to controlled drug release. Advances in the design of film-forming systems open a new generation of these systems.

The potential of polymeric film-forming systems as sustained delivery platforms for topical drugs

INTRODUCTION

Dosing regimens requiring multiple daily applications frequently result in poor patient compliance, especially in the treatment of chronic skin diseases. Consequently, development of sustained delivery systems for topical drugs permitting less frequent dosing is of continuing interest for dermatological therapy.

AREAS COVERED

This potential of polymeric film-forming systems (FFS), created in situ on the skin, as sustained delivery platforms for topical drug delivery is reviewed. Key formulation parameters that determine delivery efficiency are considered focussing on those that permit a drug reservoir to be established in the upper layers of the skin and/or on the skin surface from which release can be sustained over a prolonged period. The advantageous and superior cosmetic attributes of FFS (compared to conventional semi-solid formulations) that offer significantly improved patient compliance are also addressed.

EXPERT OPINION

The promise of polymeric FFS as convenient and aesthetic platforms for sustained topical drug delivery is clear. Manipulation of the formulation allows the delivery profile to be customized and optimized to take advantage of both a rapid, initial input of drug into the skin (likely due to a transient period of supersaturation) and a slower, controlled release over an extended time from the residual film created thereafter.

Spray-on transdermal drug delivery systems

INTRODUCTION

Transdermal drug delivery possesses superior advantages over other routes of administration, particularly minimizing first-pass metabolism. Transdermal drug delivery is challenged by the barrier nature of skin. Numerous technologies have been developed to overcome the relatively low skin permeability, including spray-on transdermal systems.

AREAS COVERED

A transdermal spray-on system (TSS) usually consists of a solution containing the drug, a volatile solvent and in many cases a chemical penetration enhancer. TSS promotes drug delivery via the complex interplay between solvent evaporation and drug-solvent drag into skin. The volatile solvent carries the drug into the upper layers of the stratum corneum, and as the volatile solvent evaporates, an increase in the thermodynamic activity of the drug occurs resulting in an increased drug loading in skin.

EXPERT OPINION

TSS is easily applied, delivering flexible drug dosage and associated with lower incidence of skin irritation. TSS provides a fast-drying product where the volatile solvent enables uniform drug distribution with minimal vehicle deposition on skin. TSS ensures precise dose administration that is aesthetically appealing and eliminates concerns of residual drug associated with transdermal patches. Furthermore, it provides a better alternative to traditional transdermal products due to ease of product development and manufacturing.

Development of transdermal therapeutic formulation of CNS5161, a novel N-methyl-D-aspartate receptor antagonist, by utilizing pressure-sensitive adhesives I

The aim of this study was to investigate the feasibility of percutaneous absorption of CNS5161, a novel N-methyl-D-aspartate (NMDA) receptor antagonist developed as a potential treatment for neuropathic pain and other neurological disorders. Six pressure-sensitive adhesives (PSA) with different physicochemical properties, namely, styrene-isoprene-styrene (1) (SIS(1)), styrene-isoprene-styrene (2) (SIS(2)), silicone, acrylate with a hydroxyl group (acrylate(OH)), acrylate without a functional group (acrylate(none)) and acrylate with a carboxyl group (acrylate(COOH)), were investigated for their release of CNS5161 and its subsequent skin permeability. Among the adhesives examined, silicone PSA provided the highest value of transdermal flux of CNS5161, which could be attributable to the highest release rate from it due to its very high thermodynamic activity. Although CNS5161 was also in the supersaturated state in SIS(1) and SIS(2) PSAs, the release and transdermal permeation from these adhesives were slower than those from silicone PSA. As for the acrylic PSAs, the highest release rate and permeability of CNS5161 were observed for acrylate(OH) PSA, followed by acrylate(none) and acrylate(COOH) PSAs, but none of them was better in terms of either the release or the permeability of CNS5161 than silicone PSA. These results clearly indicated that silicone PSA would be the most suitable for transdermal delivery of CNS5161 and silicone PSA containing 10% CNS5161 would be suitable for clinical use in humans.

Dynamic in-situ eutectic formation for topical drug delivery

Objectives

The relationship between the solution-state chemistry of eutectic systems and their transmembrane transport characteristics is difficult to define as these mixtures are sensitive to delivery vehicle-induced penetration enhancement. Through in-situ formation of a molten eutectic mixture using highly evaporative sprays this study aimed to gain an understanding of solution-state thermodynamic and chemical properties of eutectic combinations pertinent to transmembrane transport in the absence of a delivery vehicle.

Methods

In-situ molten lidocaine–prilocaine eutectics were formed using a hydroflouroalkane (HFA) propellant. Transport through silicone membranes and human skin in upright Franz diffusion cells was determined using in-house manufactured creams as controls.

Key findings

The application of the two drugs in an HFA spray produced a molten oil even when the melting point of the drug mixture was above the experimental temperature at the membrane surface. In the absence of vehicle effects, molecule presentation to the membrane interface was most effective using a lidocaine-rich mixture of 0.7% w/w lidocaine:prilocaine – 1985.06 ± 128.87 µg/h/cm2.

Conclusions

There appeared to be no link between melting point and transmembrane transport of lidocaine:prilocaine from a eutectic mixture. The rate of drug presentation to the membrane interface, which was highest in drug-rich, high-activity molten eutectic mixtures, was the driver for transmembrane transport in the absence of significant barrier interactions.

Manipulation of corticosteroid release from a transiently supersaturated topical metered dose aerosol using a residual miscible co-solvent

PURPOSE

The creation of supersaturation transiently after application overcomes the issue of drug instability. However, if the solvents used to drive supersaturation evaporate too quickly, drug recrystallisation or rapid film drying can occur which will inhibit drug release. As such the effects of a residual solvent, poly(ethylene glycol) 400 (PEG), on the release, mobility and supersaturation kinetics of a transiently supersaturated formulation were studied.

MATERIALS AND METHODS

Metered dose aerosol (MDA) formulations consisting of hydrofluoroalkane 134a, ethanol, poly(vinyl pyrrolidone) K90, beclomethasone dipropionate (BDP), and 0%, 5% or 10% w/w PEG were prepared in canisters sealed with metered dose valves and tested for release and adhesion over time.

RESULTS

The addition of 10% PEG to the MDA formulation resulted in a significant reduction (p < 0.05) in steady state drug release rate (230.4 +/- 17.3 microg/cm(2)/h for 0% PEG MDA, 83.6 +/- 4.9 microg/cm(2)/h for 10% PEG MDA). The presence of PEG caused a delay in dose depletion (2 h for 0% PEG MDA versus 4 h for 10% PEG), retarded supersaturation kinetics and increased film drying time.

CONCLUSION

Whilst equivalent amounts of BDP were released, the residual solvent altered the drug release profile to achieve more constant delivery.