Mixtures that are intended for topical application to the skin to achieve local or systemic effects are ancient. The early Egyptians applied natural products like henna, Aloe Vera, milk and honey to the skin well over 6000 years ago. The Chinese empress used herbal concoctions for skincare and the ancient Greeks were renowned for their topical ‘’galenicals’’. Transdermal and topical pharmaceuticals are prescribed and administered routinely all over the world; they constitute around 15%–20% of all repeat prescriptions with topical steroids being the most commonly prescribed. OTC (Over-The-Counter) skin products such as non-steroidal anti-inflammatory drugs, lubricants, moisturisers and emollients are very popular. The annual skincare market–worldwide- is estimated to be in the region of hundreds of billions of $US.
The human skin is the largest body organ; in a healthy adult, the skin surface area is approximately 1.7–1.8 m2; it comprises 11% of the total body mass. It is a formidable barrier and helps protect internal organs from the ingress of microorganisms, chemical and physical insults. The intact skin remains a challenge to overcome by pharmaceutical formulators and drug delivery scientists. Conventional skin formulations that are intended for topical, regional and transdermal drug delivery are in the form of simple solutions, lotions, creams, ointments, gels, foams and aerosols. Prefabricated transdermal patches were first introduced to the US market in the late 1970’s with the FDA approval of scopolamine patches for motion sickness. Since then numerous transdermal patches (matrix or membrane-based) have been approved and introduced worldwide for clinical indications such as hormone replacement therapy (HRT), pain management, nicotine replacement therapy, angina pectoris management, depression, ADHD, Parkinson’s and Alzheimer’s. In most of the aforementioned cases the developed patch has helped to either overcome drug delivery challenges and/or to improve patient compliance.
Recent research on the delivery of macromolecules and vaccines across the stratum corneum through the application of external triggers such as low density electrical current (iontophoresis) and ultrasound (sonophoresis); the use of compressed gases (needless injectors) and more recently through the use of solid or hollow microneedles is promising. From a clinical perspective, In situ topical treatment of melanoma and actinic keratosis with immunemodulators and the delivery challenges associated with persistent skin conditions like psoriasis remain unresolved with conventional topical formulations. Hence, the importance of a systematic approach to research and develop skin formulations; this should be underpinned by thorough and comprehensive understanding of the patient (customer) needs, drug molecule, the drug delivery system, scale up and manufacturing challenge, regulatory process and cost-effectiveness.
This issue of PDT focusses on topical and transdermal formulations and drug delivery systems. Topics covered include: Matrix-type transdermal films to enhance simvastatin skin permeability; Microemulsion-based hydrogels for dermal delivery of benzocaine; Ionic liquids as novel skin permeation enhancers for drug transdermal delivery; Novel organogels for topical delivery of naproxen; Formulation factors affecting the isomerization rate of betamethasone-17-valerate in a developmental hydrophilic cream; Topical colloidal indocyanine green-mediated photodynamic therapy for treatment of basal cell carcinoma; Mucoadhesive in situ gel formulation for vaginal delivery of clotrimazole; Evaluation of γ-cyclodextrin effect on permeation of lipophilic drugs; Monocyclic monoterpenes as penetration enhancers of ligustrazine hydrochloride; A prodrug approach to enhance azelaic acid percutaneous availability; How can lipid nanocarriers improve transdermal delivery of olanzapine; Influence of sonophoresis on transdermal drug delivery of hydrophilic compound-loaded lipid nanocarriers; Carbon nanotube membranes to predict skin permeability of compounds; Effect of chitosan coating on microemulsion for effective dermal clotrimazole delivery; Recent progress in transdermal sonophoresis; Progress in the use of microemulsions for transdermal and dermal drug delivery; Implantable and transdermal polymeric drug delivery technologies for the treatment of central nervous system disorders and Methods for the determination of the substantivity of topical formulations.
I hope that you will enjoy this issue.
Sincerely,
Raid Alany
School of Life Sciences, Pharmacy and Chemistry, Kingston University London, London, UK;
School of Pharmacy, The University of Auckland, Auckland, New Zealand