Ablative fractional laser enhances MAL-induced PpIX accumulation: Impact of laser channel density, incubation time and drug concentration

• Ablative fractional laser (AFL) enhances accumulation of topical provided photosensitizer.
• PpIX formation is accelerated by AFL-exposure in healthy human skin.
• Protoporfyrin IX (PpIX) levels increase with AFL densities up to 5% coverage.
• Laser densities above 5% exert a minor additional effect on PpIX accumulation.
• Methyl aminolevulinate 80 and 160 mg/g induce similar PpIX levels after AFL 1–5%.

Background and ObjectivesPretreatment of skin with ablative fractional laser enhances accumulation of topical provided photosensitizer, but essential information is lacking on the interaction between laser channel densities and pharmacokinetics. Hence our objectives were to investigate how protoporphyrin accumulation was affected by laser densities, incubation time and drug concentration.MethodsWe conducted the study on the back of healthy male volunteers (n = 11). Test areas were pretreated with 2940 nm ablative fractional Er:YAG laser, 11.2 mJ per laser channel using densities of 1, 2, 5, 10 and 15% (AFL 1–15%). Control areas received pretreatment with curettage or no pretreatment. Methyl aminolevulinate (MAL) was applied under occlusion in concentrations of 0, 80 and 160 mg/g. MAL-induced protoporphyrin fluorescence was quantified with a handheld photometer after 0, 30, 60, 120 and 180 min incubation. The individual fluorescence intensity reached from the highest density (15%) and longest MAL 160 mg/g incubation time (180 min) was selected as reference (100%) for other interventional measurements.ResultsA low laser density of 1% markedly enhanced fluorescence intensities from 34% to 75% (no pretreatment vs. AFL 1%, MAL 160 mg/g, 180 min; p < 0.001). Furthermore, fluorescence intensities increased substantially by enhancing densities up to 5% (p ≤ 0.0195). Accumulation of protoporphyrins was accelerated by laser exposure. Thus, laser exposure of 5% density and a median incubation time of 80 min MAL (range 46–133 min) induced fluorescence levels similar to curettage and 180 min incubation. Furthermore, MAL 80 and 160 mg/g induced similar fluorescence intensities in skin exposed to laser densities of 1, 2 and 5% (p > 0.0537, 30–180 min).ConclusionMAL-induced protoporphyrin accumulation is augmented by enhancing AFL densities up to 5%. Further, this model indicates that incubation time as well as drug concentration of MAL may be reduced with laser pretreatment.