Transdermal delivery of physostigmine: effects of enhancers and pressure-sensitive adhesives

Long-acting transdermal drug delivery formulations: Current developments and innovative pharmaceutical approaches

Transdermal administration remains an active research and development area as an alternative route for long-acting drug delivery. It avoids major drawbacks of conventional oral (gastrointestinal side effects, low drug bioavailability, and need for multiple dosing) or parenteral routes (invasiveness, pain, and psychological stress and bio-hazardous waste generated from needles), thereby increasing patient appeal and compliance. This review focuses on the current state of long-acting transdermal drug delivery, including adhesive patches, microneedles, and molecularly imprinted polymeric systems. Each subsection describes an approach including key considerations in formulation development, design, and process parameters with schematics. An overview of commercially available conventional (adhesive) patches for long-acting drug delivery (longer than 24 h), the reservoir- and matrix-type systems under preclinical evaluation, as well as the advanced transdermal formulations, such as the core-shell, nanoformulations-incorporated and stimuli-responsive microneedles, and 3D-printed and molecularly imprinted polymers that are in development, is also provided. Finally, we elaborated on translational aspects, challenges in patch formulation development, and future directions for the clinical advancement of new long-acting transdermal products.

Effect of Different Pressure-Sensitive Adhesives on Performance Parameters of Matrix-Type Transdermal Delivery Systems

Matrix-type transdermal delivery systems (TDS) are comprised of the drug dissolved or dispersed in a pressure-sensitive adhesive (PSA) matrix and are designed to provide a controlled delivery through the skin and into systemic circulation. PSAs can directly affect the permeation, release, and performance characteristics of the system. In this study we aimed to design and characterize transdermal delivery systems formulated with lidocaine-as the model drug-loaded in different PSAs, including silicone, polyisobutylene (PIB), and acrylate. TDS containing lidocaine at its saturation points were prepared by the solvent casting method. In vitro permeation studies across dermatomed porcine ear skin were performed using Franz diffusion cells. In vitro release studies were carried out using USP apparatus 5 (paddle over disk). The cumulative amount permeated from the acrylate was significantly higher than silicone and PIB. The acrylate TDS contained a ten times higher drug amount than silicone TDS, but the permeation flux was only two folds higher. Results also showed the release of drug does not linearly correlate to saturation, as the silicone TDS comprising of the lowest amount of drug loading, showed the highest percentage release indicating the choice of PSA affected the drug release and permeation profile.

A statistical experimental design approach to evaluate the influence of various penetration enhancers on transdermal drug delivery of buprenorphine

A series of drug-in-adhesive transdermal drug delivery systems (patch) with different chemical penetration enhancers were designed to deliver drug through the skin as a site of application. The objective of our effort was to study the influence of various chemical penetration enhancers on skin permeation rate and adhesion properties of a transdermal drug delivery system using Box-Behnken experimental design. The response surface methodology based on a three-level, three-variable Box-Behnken design was used to evaluate the interactive effects on dependent variables including, the rate of skin permeation and adhesion properties, namely peel strength and tack value. Levulinic acid, lauryl alcohol, and Tween 80 were used as penetration enhancers (patch formulations, containing 0-8% of each chemical penetration enhancer). Buprenorphine was used as a model penetrant drug. The results showed that incorporation of 20% chemical penetration enhancer into the mixture led to maximum skin permeation flux of buprenorphine from abdominal rat skin while the adhesion properties decreased. Also that skin flux in presence of levulinic acid (1.594 μg/cm(2) h) was higher than Tween 80 (1.473 μg/cm(2) h) and lauryl alcohol (0.843 μg/cm(2) h), and in mixing these enhancers together, an additional effect was observed. Moreover, it was found that each enhancer increased the tack value, while levulinic acid and lauryl alcohol improved the peel strength but Tween 80 reduced it. These findings indicated that the best chemical skin penetration enhancer for buprenorphine patch was levulinic acid. Among the designed formulations, the one which contained 12% (wt/wt) enhancers exhibited the highest efficiency.

Development and evaluation of α-asarone transdermal patches based on hot-melt pressure-sensitive adhesives

A hot-melt, pressure-sensitive adhesive (HMPSA) based on styrene-isoprene-styrene was prepared, and its compatibility with various transdermal penetration enhancers was investigated. The effect of penetration enhancers on the adhesion properties of HMPSA was also studied. A drug-in-adhesive patch was formulated using α-asarone as a model drug, and penetration enhancers were screened by an in vitro transdermal study across excised pig skin. The pharmacokinetics in rabbits was also studied. The results show that HMPSA was miscible with most penetration enhancers (azone, menthol, isopropyl myristate, 1-methyl-pyrrolidinone, N,N-dimethylformamide, oleic acid), apart from propylene glycol. Penetration enhancers had a plasticizer-like effect that decreased the peel strength and shear strength of HMPSA. A combination of 1% oleic acid and 4% menthol had the highest in vitro penetration rate and was selected for patch preparation. The patch formulation was optimized by replacing some of the plasticizer by penetration enhancers to achieve good adhesion and effective transdermal flux. The final patch showed a high efficiency, with a relative bioavailability of 1,494%. This suggests that HMPSA may be a promising material for drug-delivery patches.

The influence of the polar head and the hydrophobic chain on the skin penetration enhancement effect of poly(ethylene glycol) derivatives

The effect of a homologue series of nonionic surfactants, namely poly(ethylene glycol) (PEG) fatty acid esters, differing in oxyethylene (PEG 8, PEG 12, and PEG 40) and fatty acid (stearate, mono and di-laurate, and mono and di-oleate) chain lengths, on in vitro skin permeability of ketoprofen (KTP) vehicled in plasters was investigated. The drug diffusion through hairless mouse skin as well as the effect of the surfactant type and strength was studied by Franz diffusion cells and ATR-FTIR spectroscopy. The use of PEG stearate series revealed that the surfactant with the largest polar head, namely PEG 40, was ineffective in enhancing the skin permeation of KTP, independently of the plaster concentrations. The effect of the hydrophobic chain was investigated only by using the shortest oxyethylene chains. The experimental results revealed that the oxyethylene chain length of surfactants appeared to be more influent than the alkyl chain. The prediction of the absorption enhancing capability of these PEG derivatives appeared related to the vehicle other than the proper combination of the number of ethylene oxide groups and alkyl groups.

Evaluation of the Transdermal Permeation Behavior of Proterguride from Drug in Adhesive Matrix Patches Through Hairless Mouse Skin

The transdermal in vitro permeation behavior of the highly potent dopamine agonist Proterguride was investigated using hairless mouse skin as a model membrane. Drug in adhesive matrix formulations based on different types of pressure-sensitive adhesives (Eudragit E 100 and Gelva7883 as acrylates, Oppanol B 15 SFN as polyisobutylene, and BioPSA 7-4202 as silicone) with a drug load of 3% by weight were manufactured. All patches were examined for drug crystallization by polarized microscopy immediately after the manufacturing process and after storage for 30 days in sealed aluminium laminate bags at ambient temperature and at 40 degrees C, respectively. Furthermore, the influence of the drug load in acrylate-based formulations onto the steady-state flux of Proterguride was examined. The Eudragit E 100 system delivered a significantly higher steady-state flux than the systems based on Oppanol B 15 SFN and also a somewhat higher steady-state flux than the Gelva-based patch. An addition of 10% by weight of the crystallization inhibitor povidone 25 did not significantly influence the steady-state flux of Proterguride from acrylate matrices. The lipophilic silicone and polyisobutylene adhesives facilitated drug crystallization within the short storage periods at both conditions, probably due to the absence of povidone 25, which was incompatible with these polymers. Varying the drug load in acrylate-based formulations led to a linear increase of the steady-state flux until the steady-state flux of Proterguride leveled off and the patches tended to drug crystallization. It was found that Gelva-based patches show good physical stability, good skin adhesion, and moderate flux values and, thus, can be evaluated as a basis for a suitable formulation for the transdermal administration of Proterguride.