• Zhirong Yang, Yuan Zhang, Elvira Lazic Mosler, Jing Hu, Hang Li, Yanchang Zhang, Jia Liu, and Qian Zhang.
• School of Clinical Medicine, University of Cambridge, Primary Care Unit, Department of Public Health and Primary Care, Strangeways Research Laboratory, 2 Worts' Causeway, Cambridge, UK, CB1 8RN.
• Cochrane Db Syst Rev. 2020 Mar 16; 3 (3): CD011154CD011154.

BackgroundAcne is a common, economically burdensome condition that can cause psychological harm and, potentially, scarring. Topical benzoyl peroxide (BPO) is a widely used acne treatment; however, its efficacy and safety have not been clearly evaluated.ObjectivesTo assess the effects of BPO for acne.Search MethodsWe searched the following databases up to February 2019: the Cochrane Skin Specialised Register, CENTRAL, MEDLINE, Embase, and LILACS. We also searched five trials registers and checked the reference lists of relevant randomised controlled trials (RCTs) and systematic reviews.Selection CriteriaWe included RCTs that compared topical BPO used alone (including different formulations and concentrations of BPO) or as part of combination treatment against placebo, no treatment, or other active topical medications for clinically diagnosed acne (used alone or in combination with other topical drugs not containing BPO) on the face or trunk.Data Collection And AnalysisWe used standard methodological procedures as expected by Cochrane. Primary outcome measures were 'participant global self-assessment of acne improvement' and 'withdrawal due to adverse events in the whole course of a trial'. 'Percentage of participants experiencing any adverse event in the whole course of a trial' was a key secondary outcome.Main ResultsWe included 120 trials (29,592 participants randomised in 116 trials; in four trials the number of randomised participants was unclear). Ninety-one studies included males and females. When reported, 72 trials included participants with mild to moderate acne, 26 included participants with severe acne, and the mean age of participants ranged from 18 to 30 years. Our included trials assessed BPO as monotherapy, as add-on treatment, or combined with other active treatments, as well as BPO of different concentrations and BPO delivered through different vehicles. Comparators included different concentrations or formulations of BPO, placebo, no treatment, or other active treatments given alone or combined. Treatment duration in 80 trials was longer than eight weeks and was only up to 12 weeks in 108 trials. Industry funded 50 trials; 63 trials did not report funding. We commonly found high or unclear risk of performance, detection, or attrition bias. Trial setting was under-reported but included hospitals, medical centres/departments, clinics, general practices, and student health centres. We reported on outcomes assessed at the end of treatment, and we classified treatment periods as short-term (two to four weeks), medium-term (five to eight weeks), or long-term (longer than eight weeks). For 'participant-reported acne improvement', BPO may be more effective than placebo or no treatment (risk ratio (RR) 1.27, 95% confidence interval (CI) 1.12 to 1.45; 3 RCTs; 2234 participants; treatment for 10 to 12 weeks; low-certainty evidence). Based on low-certainty evidence, there may be little to no difference between BPO and adapalene (RR 0.99, 95% CI 0.90 to 1.10; 5 RCTs; 1472 participants; treatment for 11 to 12 weeks) or between BPO and clindamycin (RR 0.95, 95% CI 0.68 to 1.34; 1 RCT; 240 participants; treatment for 10 weeks) (outcome not reported for BPO versus erythromycin or salicylic acid). For 'withdrawal due to adverse effects', risk of treatment discontinuation may be higher with BPO compared with placebo or no treatment (RR 2.13, 95% CI 1.55 to 2.93; 24 RCTs; 13,744 participants; treatment for 10 to 12 weeks; low-certainty evidence); the most common causes of withdrawal were erythema, pruritus, and skin burning. Only very low-certainty evidence was available for the following comparisons: BPO versus adapalene (RR 1.85, 95% CI 0.94 to 3.64; 11 RCTs; 3295 participants; treatment for 11 to 24 weeks; causes of withdrawal not clear), BPO versus clindamycin (RR 1.93, 95% CI 0.90 to 4.11; 8 RCTs; 3330 participants; treatment for 10 to 12 weeks; causes of withdrawal included local hypersensitivity, pruritus, erythema, face oedema, rash, and skin burning), erythromycin (RR 1.00, 95% CI 0.07 to 15.26; 1 RCT; 60 participants; treatment for 8 weeks; withdrawal due to dermatitis), and salicylic acid (no participants had adverse event-related withdrawal; 1 RCT; 59 participants; treatment for 12 weeks). There may be little to no difference between these groups in terms of withdrawal; however, we are unsure of the results because the evidence is of very low certainty. For 'proportion of participants experiencing any adverse event', very low-certainty evidence leaves us uncertain about whether BPO increased adverse events when compared with placebo or no treatment (RR 1.40, 95% CI 1.15 to 1.70; 21 RCTs; 11,028 participants; treatment for 10 to 12 weeks), with adapalene (RR 0.71, 95% CI 0.50 to 1.00; 7 RCTs; 2120 participants; treatment for 11 to 24 weeks), with erythromycin (no participants reported any adverse events; 1 RCT; 89 participants; treatment for 10 weeks), or with salicylic acid (RR 4.77, 95% CI 0.24 to 93.67; 1 RCT; 41 participants; treatment for 6 weeks). Moderate-certainty evidence shows that the risk of adverse events may be increased for BPO versus clindamycin (RR 1.24, 95% CI 0.97 to 1.58; 6 RCTs; 3018 participants; treatment for 10 to 12 weeks); however, the 95% CI indicates that BPO might make little to no difference. Most reported adverse events were mild to moderate, and local dryness, irritation, dermatitis, erythema, application site pain, and pruritus were the most common.Authors' ConclusionsCurrent evidence suggests that BPO as monotherapy or add-on treatment may be more effective than placebo or no treatment for improving acne, and there may be little to no difference between BPO and either adapalene or clindamycin. Our key efficacy evidence is based on participant self-assessment; trials of BPO versus erythromycin or salicylic acid did not report this outcome. For adverse effects, the evidence is very uncertain regarding BPO compared with adapalene, erythromycin, or salicylic acid. However, risk of treatment discontinuation may be higher with BPO compared with placebo or no treatment. Withdrawal may be linked to tolerability rather than to safety. Risk of mild to moderate adverse events may be higher with BPO compared with clindamycin. Further trials should assess the comparative effects of different preparations or concentrations of BPO and combination BPO versus monotherapy. These trials should fully assess and report adverse effects and patient-reported outcomes measured on a standardised scale.Copyright © 2020 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.

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