(T0930-01-04) Impact of Penetration Enhancers on Salbutamol Permeation Across Murine Skin

Purpose: Obesity is on the rise worldwide, with around 39% of adults being overweight. This is associated with many health complications and could lead to death. Salbutamol, as a β2 agonist, is a promising therapeutic agent against obesity, as it has the ability to induce thermogenesis [1]. This process can be used to counteract the hypercaloric state of obesity. To avoid the side effects of systemic administration, application through the skin is beneficial. While it has been shown earlier that salbutamol from patches can penetrate the skin [2], a feasibility of permeation from solutions is pending and would simplify application. The use of penetration enhancers such as glycerol, dimethyl sulfoxide (DMSO) and ethanol, which are also solvents, may be advantageous for this purpose. Glycerol in particular is of interest due to its skin compatibility and its penetration-enhancing properties [3, 4]. In this study, the influence of penetration-enhancing solvents on the permeated amount of salbutamol hemisulfate is investigated in an ex vivo mouse setup.

Methods: Salbutamol hemisulfate solutions were prepared in mixtures of glycerol, DMSO and ethanol by stirring at 500 rpm for 30 min in the absence of light. For the Franz cell experiments, standardized, jacked Franz cells with an area of 1.00 cm² were used. Mouse skin (600 µm thickness) with shaved fur was used as a barrier membrane, which was freshly inserted into the Franz cells. Phosphate-buffered saline (PBS) pH 7.4 with 6% Brij 98 (v/v) was used as the acceptor medium and 200 µL salbutamol hemisulfate solution was added to the donor compartment (infinite dose). The temperature on the skin was 32°C. Samples were collected over a period of 24 h and analyzed for drug content by ultra-performance liquid chromatography (UPLC). The analysis was performed on an LC-2040C 3D Plus system (Shimadzu, Kyoto, Japan) equipped with a C18 reversed-phase column (Inertsil ODS-3, 150 mm length, 2.1 mm inner diameter, 3 µm particle size). The flow rate was set to 0.3 mL/min, and the eluent consisted of 6/94 (%v/v) methanol, and MilliQ with 0.2% (v/v) triethylamine solution adjusted to pH 3 with orthophosphoric acid. The column temperature was kept at 40°C and the injection volume was 2 µL.

Results: When comparing the glycerol formulations, the amount of salbutamol hemisulfate that permeated through the skin into the acceptor compartment over 24 h was found to be lowest with DMSO/glycerol 50/50 and highest with ethanol/glycerol 50/50, which was a significant difference between these two formulations (p < 0.05). The flux calculated from the slope of the linear part of the curve was lowest for DMSO/glycerol 50/50 and highest for ethanol/glycerol 50/50. Formulations with DMSO were characterized by a lower flux, compared to formulations with ethanol. However, it should be noted that the two formulations containing MilliQ instead of glycerol show a significantly higher permeation of the API over 24 h as well as a higher flux. Ethanol can change the barrier properties by rearranging lipids and proteins, which may explain the higher permeation. Water-containing formulations showed a significantly increased permeated amount of API and flux compared to formulations containing glycerol. This can be attributed to the increased solubility of salbutamol hemisulfate in water. A combination of the penetration enhancing properties of ethanol and the high solubility of the API in water led to the highest measured flux and permeated amount of salbutamol hemisulfate over mouse skin with 986.7 ± 127.1 µg/cm² in 24h.

Conclusion: Permeation of salbutamol hemisulfate was generally successful at infinite doses. This study showed the influence of permeation enhancers such as ethanol and glycerol on the permeated amount of the API and the flux. In contrast to the hypothesis that glycerol would ameliorate skin permeation, water led to an increased permeation rate of the API.

References: [1] Straat ME, Hoekx CA, van Velden FHP, Pereira Arias-Bouda LM, Dumont L, Blondin DP, et al. Stimulation of the beta-2-adrenergic receptor with salbutamol activates human brown adipose tissue. Cell Rep Med. 2023;4:100942. doi:10.1016/j.xcrm.2023.100942.
[2] Narasimha Murthy S, Hiremath SR. Clinical pharmacokinetic and pharmacodynamic evaluation of transdermal drug delivery systems of salbutamol sulfate. Int J Pharm. 2004;287:47–53. doi:10.1016/j.ijpharm.2004.08.018.
[3] Björklund S, Engblom J, Thuresson K, Sparr E. Glycerol and urea can be used to increase skin permeability in reduced hydration conditions. Eur J Pharm Sci. 2013;50:638–45. doi:10.1016/j.ejps.2013.04.022.
[4] Bettinger J, Gloor M, Peter C, Kleesz P, Fluhr J, Gehring W. Opposing Effects of Glycerol on the Protective Function of the Horny Layer against Irritants and on the Penetration of Hexyl Nicotinate. Dermatology. 1998;197:18–24.

Acknowledgements: The authors thank the German Federal Ministry of Education and Research for financial support (03VP11020 "Miraskin").


Permeated amount (A) and flux (B) of salbutamol hemisulfate from a formulation with 1% active ingredient and combinations of different solvents through the skin of mice.