Background Severe acne vulgaris has limited therapeutic options. Objectives To evaluate photodynamic therapy (PDT) using topical methyl aminolaevulinate (MAL, 80 mg g-1) as the photosensitizer in severe facial acne. Methods A double-blind, randomized, vehicle-controlled multicentre trial in 153 patients (aged 12-35 years) with severe facial acne [Investigator's Global Assessment (IGA) score 4; 25-75 inflammatory lesions with ≤ 3 nodules; 20-100 noninflammatory lesions]. Treatment (four treatments 2 weeks apart) involved incubation with MAL (n = 100) or vehicle cream (n = 53) for 1·5 h under occlusion, then illumination (635-nm red light, total dose 37 J cm-2). IGA assessment and standardized lesion counts were performed before each treatment and 12 weeks after the first treatment. Treatment success was defined as improvement from baseline in IGA by ≥ 2 grades at 12 weeks. Safety assessments were for pain (10-cm visual analogue scale, immediately after illumination), erythema (four-point rating scale) and adverse events. Results At 12 weeks, PDT using MAL 80 mg g-1 reduced inflammatory lesions vs. vehicle PDT (mean change -15·6 vs. -7·8, P = 0·006; mean percentage change -37·3% vs. -16·2%, P = 0·003). However, noninflammatory lesions did not decrease significantly (mean change -11·8 vs. -10·7, P = 0·85; mean percentage change -28·6% vs. -24·9%, P = 0·72). Treatment success rates were greater with MAL-PDT 80 mg g-1 (44% vs. 26%, P = 0·013). Pain was low and manageable by briefly pausing illumination. There was similar pain or erythema with successive treatments. Conclusions PDT using topical MAL 80 mg g-1 and red light may offer promise for severe acne vulgaris.
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