Abstract
Polyethylene glycols (PEGs) and PEG derivatives are used in a range of cosmetic and pharmaceutical products. However, few studies have investigated the influence of PEGs and their related derivatives on skin permeation, especially when combined with other solvents. Previously, we reported niacinamide (NIA) skin permeation from a range of neat solvents including propylene glycol (PG), Transcutol® P (TC), dimethyl isosorbide (DMI), PEG 400 and PEG 600. In the present work, binary and ternary systems composed of PEGs or PEG derivatives combined with other solvents were investigated for skin delivery of NIA. In vitro finite dose studies were conducted (5 μL/cm2) in porcine skin over 24 h. Higher skin permeation of NIA was observed for all vehicles compared to PEG 400. However, overall permeation for the binary and ternary systems was comparatively low compared with results for PG, TC and DMI. Interestingly, values for percentage skin retention of NIA for PEG 400:DMI and PEG 400:TC were significantly higher than values for DMI, TC and PG (p < 0.05). The findings suggest that PEG 400 may be a useful component of formulations for the delivery of actives to the skin rather than through the skin. Future studies will expand the range of vehicles investigated and also look at skin absorption and residence time of PEG 400 compared to other solvents.
Highlights
The skin is the largest organ of the human body and serves as a unique interface between humans and the environment
The solubility parameters for Polyethylene glycols (PEGs)-6-CCG and the binary systems composed of PEG-6-CCG were not calculated, as this solvent is a mixture of polyethylene glycol derivatives of a range of caprylic/capric glyceride acids [30]
The NIA solubility value for PEG 400:propylene glycol (PG) (50:50) was 25.6 ± 1.1% (w/v). This value was significantly higher (Table 1) than the results obtained for PEG 400:PEG-6-CCG (50:50), PEG 400:dimethyl isosorbide (DMI) (50:50), PEG 400:Transcutol® P (TC) (50:50) and PEG 400:PG:DMI (50:25:25), (p < 0.05)
Summary
The skin is the largest organ of the human body and serves as a unique interface between humans and the environment. This membrane is a formidable barrier, preventing the egress of water, the ingress of toxins and offers protection against ultraviolet (UV) radiation [1,2]. Skin serves as a route for the administration of therapeutic molecules for both local and systemic effects [3]. The primary challenge in the skin penetration process is the passage of molecules through the outermost layer, the stratum corneum (SC). The SC consists of eight to sixteen layers of [4] keratinized corneocytes embedded in a lipid domain. To improve the efficacy of topical and transdermal delivery, various formulation components have been investigated for their potential to facilitate permeation of actives through the SC
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