Dear Colleagues,

The market approval of a generic product requires the demonstration of bioequivalence (BE) against an innovator reference product in order to ensure safety and efficacy. Unlike extravascular dosage forms where well-established methods and regulatory guidelines are available for BE assessment, procedures or guidelines for the BE of topical dosage forms intended for local action, apart from the US FDA’s vasoconstrictor assay (VCA), are conspicuously absent. Most regulatory authorities usually require lengthy and expensive comparative clinical endpoint studies in patients. More recently, considerable efforts have been directed towards the development and validation of surrogate models to demonstrate the BE of topical products for local action and facilitate the faster entry of generic products into the market. Requirements ensuring that such topical generic products are designed to match an approved reference product have been set out by regulatory authorities, where emphasis has been placed on specific quality properties such as qualitative (Q1), quantitative (Q2) and—particularly for semi-solid formulations—similarity in formulation microstructure (Q3). Currently, relatively few surrogate approaches to the assessment of the BE of topical dosage forms for local action have been explored. The more prominent methods include tape stripping, dermal microdialysis, open-flow microperfusion and, more recently, the acceptance of biowaivers using in vitro release and permeation tests. In the latter instance, the US FDA has issued specific product guidelines (SPGs) for topicals.

This Special Issue on the bioavailability (BA) and bioequivalence (BE) of topical formulations intended for local action will focus on research and review papers discussing applications of validated methods used to assess BE of topical dosage forms not intended for absorption, and will include both in vivo and in vitro methods.

We welcome articles dealing with all aspects of the BA/BE of topical dosage forms for local action, and invites researchers and drug developers to submit their original research or review articles with expert opinions and perspectives in this area.

Prof. Dr. Isadore Kanfer
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Pharmaceutics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2900 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• bioequivalence
• bioavailability
• biowaivers
• topical dosage forms for local action
• topical corticosteroids
• vasoconstrictor assay (VCA)
• skin blanching
• chromameter
• tape stripping
• dermatopharmacokinetics
• dermal microdialysis
• in vitro release tests (IVRTs)
• in vitro permeation tests (IVPTs)
• ex vivo permeation tests
• dermal open flow microperfusion (dOFM)
• confocal Raman spectroscopy
• near-infrared (NIR) spectrometry
• product specific guidances (PSG)
• membrane diffusion
• pharmaceutical equivalence
• sameness
• Q1/Q2/Q3
• semi-solid dosage forms
• method validation
• human skin
• stratum corneum