Onychomycosis is a fungal infection of the fingernails or toenails caused by dermatophytes, nondermatophytes, moulds, and yeasts. This condition affects around 10-30% people worldwide, negatively influencing patients' quality of life, with severe outcomes in some cases. Since the nail unit acts as a barrier to exogenous substances, its physiological features hampers drug penetration, turning the onychomycosis treatment a challenge. Currently, there are several oral and topical therapies available; nevertheless, cure rates are still low and relapse rates achieves 10-53%. Also, serious side effects may be developed due to long-term treatment. In light of these facts, researchers have focused on improving topical treatments, either by modifying the vehicle or by using some physical technique to improve drug delivery trough the nail plate, hence increasing therapy effectiveness. Therefore, the aim of this paper is to explain these novel alternative approaches. First, the challenges for drug ungual penetration are presented. Then, the chemical and physical strategies developed for overcoming the barriers for drug penetration are discussed. We hope that the information gathered may be useful for the development of safer and more effective treatments for onychomycosis.

Clobetasol propionate (CLO) is a potent glucocorticoid used to treat inflammation-based skin, scalp, and hair disorders. In such conditions, hair follicles (HF) are not only the target site but can also act as drug reservoirs when certain formulations are topically applied. Recently, we have demonstrated nanostructured lipid carriers (NLC) containing CLO presenting epidermal-targeting potential. Here, the focus was evaluating the HF uptake provided by such nanoparticles in comparison to a commercial cream and investigating the influence of different physical stimuli [i.e., infrared (IR) irradiation (with and without metallic nanoparticles-MNP), ultrasound (US) (with and without vibration) and mechanical massage] on their follicular targeting potential. Nanosystems presented sizes around 180 nm (PdI < 0.2) and negative zeta potential. The formulation did not alter skin water loss measurements and was stable for at least 30 days at 5 °C. Nanoparticles released the drug in a sustained fashion for more than 3 days and increased passively about 40 times CLO follicular uptake compared to the commercial cream. Confocal images confirmed the enhanced follicular delivery. On the one hand, NLC application followed by IR for heat generation showed no benefit in terms of HF targeting even at higher temperatures generated by metallic nanoparticle heating. On the other hand, upon US treatment, CLO retention was significantly increased in deeper skin layers. The addition of mechanical vibration to the US treatment led to higher follicular accumulation compared to passive exposure to NLC without stimuli. However, from all evaluated stimuli, manual massage presented the highest follicular targeting potential, driving more than double the amount of CLO into the HF than NLC passive application. In conclusion, NLC showed great potential for delivering CLO to HF, and a simple massage was capable of doubling follicular retention.Skin, hair, and scalp-related dermatological inflammatory pathologies have been treated for decades with oral and topical glucocorticoids. Among the topical drugs under study, clobetasol propionate (CLO) stands out as the most potent one 1 . Due to its vasoconstricting, anti-inflammatory, immunosuppressive and antiproliferative effects, the drug is useful in the treatment of conditions such as eczema, atopic dermatitis, alopecia areata, frontal fibrosing alopecia, psoriasis and lichen planopilaris 2-4 . Nevertheless, continuous use of typical CLO dermatological formulations may present local side effects as skin atrophy, pruritus, folliculitis, and telangiectasia 5-7 . Even though topical treatment results in fewer adverse effects when compared to oral or parenteral administration, formulations capable of controlling drug release while targeting and enhancing drug penetration to specific skin layers can provide additional therapeutic benefits.Previous studies from our group have shown CLO-loaded nanostructured lipid carriers (NLC), produced with 1/5 th of the drug dose used in commercial formulations, presented...

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Topical and transdermal delivery has been studied over last decades and it presents advantages for the treatment of several disorders, macromolecules delivery and vaccination. The greatest challenge is to overcome the stratum corneum (SC) barrier. Compared to traditional topical formulation strategies, nano /microsystems offer advantages such as increased stability, increased loading dose, coverage of undesired colors, reduced toxicity and prolonged release of active agents. However, there are no conclusive studies demonstrating the ability of such systems to penetrate the skin in relevant therapeutic amounts. The use of physical methods holds great promise for enhancing skin permeation through the SC and for targeting hair follicles. This review discusses the characteristics and feasibility of using a dual approach employing the application of physical methods of permeation enhancement to enable the topical or transdermal delivery of drug-loaded nano/microsystems.