A molecular mechanism investigation of the
transdermal/topical absorption classification system on the basis of drug skin permeation and skin retention.
Int J Pharm 2021;
608:121082. [PMID:
34506925 DOI:
10.1016/j.ijpharm.2021.121082]
[Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 08/27/2021] [Accepted: 09/05/2021] [Indexed: 01/02/2023]
Abstract
A transdermal/topical absorption classification system for the characterization of the systemic or local delivery of drugs is the theoretical basis for the design and evaluation of transdermal/topical formulations. A classification system was established on the basis of the in vitro and in vivo skin permeation/retention behaviors of 12 model drugs. Drug skin penetration/retention exhibited a significant correlation with physicochemical parameters (log KO/W, molecular weight, polar surface area, and polarizability). Four representative model drugs were selected to clarify the molecular mechanisms of drug skin permeation/retention behaviors. The excellent lipid-disrupting effect and enhanced partitioning exhibited by propranolol (high permeation-high retention) and zolmitriptan (high permeation-low retention) via the formation of moderate H-bonds with skin lipids were proven by ATR-FTIR (ΔνasCH2 > 2 cm-1), Raman spectra (ΔLPP, SPP > 0.2 nm), and X-ray scattering (lipid crystallization) and were supported by 13C NMR results. The low lipid miscibility of zolmitriptan (ΔHzolmitriptan-lipid = 126.92 J/g) caused the low skin retention of this drug. High polarizabiltiy (α = 38.5 × 10-24 cm3) and low H-bond forming capability (EH-bond = 0 kcal/mol) restricted terbinafine (low permeation-high retention) in terms of partitioning (kD-SC = 0.09). Diclofenac (low permeation-low retention) stabilized skin lipids through the formation of strong H-bonds and exhibited excessive drug-lipid miscibility (ΔHdiclofenac-skin = -128.73 J/g), thus restricting its skin absorption. This classification system reflects the most essential drug skin absorption characteristics and provides a theoretical basis for the design of transdermal/topical formulations.
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