Fractional laser‐assisted drug delivery: Laser channel depth influences biodistribution and skin deposition of methotrexate

Background and Objective Ablative fractional laser (AFXL) facilitates delivery of topical methotrexate (MTX). This study investigates impact of laser-channel depth on topical MTX-delivery. Materials and Methods MTX (1% [w/v]) diffused for 21 hours through AFXL-exposed porcine skin in in vitro Franz Cells (n = 120). A 2,940 nm AFXL generated microscopic ablation zones (MAZs) into epidermis (11 mJ/channel, MAZ-E), superficial-dermis (26 mJ/channel, MAZ-DS), and mid-dermis (256 mJ/channel, MAZ-DM). High performance liquid chromatography (HPLC) was used to quantify MTX deposition in full-thickness skin, biodistribution profiles at specific skin levels, and transdermal permeation. Fluorescence microscopy was used to visualize UVC-activated MTX-fluorescence (254 nm) and semi-quantify MTX distribution in skin. Results AFXL increased topical MTX-delivery (P < 0.001). Without laser exposure, MTX-concentration in full-thickness skin was 0.07 mg/cm2, increasing sixfold (MAZ-E), ninefold (MAZ-DS), and 11-fold (MAZ-DM) after AFXL (P < 0.001). Deeper MAZs increased MTX-concentrations in all skin layers (P < 0.038) and favored maximum accumulation in deeper skin layers (MAZ-E: 1.85 mg/cm3 at 500 μm skin-level vs. MAZ-DM: 3.75 mg/cm3 at 800 μm, P = 0.002). Ratio of skin deposition versus transdermal permeation remained constant, regardless of MAZ depth (P = 0.172). Fluorescence intensities confirmed MTX biodistribution through coagulation zones and into surrounding skin, regardless of thickness of coagulation zones (6–47 μm, P ≥ 0.438). Conclusion AFXL greatly increases topical MTX-delivery. Deeper MAZs deliver higher MTX-concentrations than superficial MAZs, which indicates that laser channel depth may be important for topical delivery of hydrophilic molecules. Lasers Surg. Med. © 2016 Wiley Periodicals, Inc.