Abstract
This overview on skin delivery considers the evolution of the principles of percutaneous ab-sorption and skin products from ancient times to today. Over the ages, it has been recognised that products may be applied to the skin for either local or systemic effects. As our understanding of the anatomy and physiology of the skin has improved, this has facilitated the development of technologies to effectively and quantitatively deliver solutes across this barrier to specific target sites in the skin and beyond. We focus on these technologies and their role in skin delivery today and in the future.
Highlights
Ointments and potions made of animal, mineral or plant extracts were in common use in ancient Egyptian and Babylonian medicine in 3000 BC [1]
In addition to the range of drugs applied for local effects in the skin and associated tissues, nearly twenty drugs have been successfully developed for transdermal delivery using various topical dosage forms such as patches, gels and ointments and cutaneous solutions [21]
Applying this to transport across the stratum corneum membrane, and assuming that the regions below that major diffusion barrier offer essentially sink conditions, the steady-state flux can be described by the expression: J = ADC h (Eq 1)
Summary
Ointments and potions made of animal, mineral or plant extracts were in common use in ancient Egyptian and Babylonian medicine in 3000 BC [1]. A Sumerian clay tablet dates back to 2100 BC, describing a formulation made of pulverised snake and bat’s dung incorporated into an aqueous paste of plant extracts and earths for the treatment of skin disease [2]. The Persian physician Ibn Sina (best known as Avicenna, 980-1037 AD), in his treatise The Canon of Medicine, proposed that topical drugs possess two spirits or states: the soft part that penetrates the skin and the hard part that does not [4]. In the early 1970s, the Alza Corporation, through their founder Alejandro Zaffaroni, filed the first US patents describing transdermal delivery systems for scopolamine, nitroglycerin and nicotine. Topical and Transdermal Drug Delivery vantages including: (i) overcoming oral delivery limitations of vomiting and low bioavailability (e.g. due to a high liver and gut wall first-pass); (ii) providing an alternative to parenteral administration, which can be invasive, painful and risks bruising and infection; (iii) acting as a convenient, noninvasive means to achieve relatively constant and reliable blood levels over 24 to 72 hrs, whilst being able to cease the delivery at any time by removing the patch [21]
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