Jerry Tan, MD, FRCPC

Department of Medicine, University of Western Ontario, London, ON, Canada


Dapsone 5% gel for the topical treatment for acne vulgaris was recently introduced in Canada. It represents the first new anti-acne agent to gain North American regulatory approval in the past decade. Dapsone’s utility is attributable to its anti-inflammatory and antimicrobial properties that improve both inflammatory and non-inflammatory acne, with more prominent effects occurring in inflammatory lesions. Short- and long-term safety and efficacy have been demonstrated. Especially for patients exhibiting sensitivities or intolerance to conventional anti-acne agents, topical dapsone is a novel addition to the treatment armamentarium.

Key Words:
acne vulgaris, dapsone, sulfone

What Is It?

Dapsone, a synthetic sulfone with an amino moiety linking two sulfone rings (4,4′-diaminodiphenyl sulfone; molecular weight 248.30), has had medical applications for more than 7 decades for treating various medical conditions including dermatitis herpetiformis, leprosy, and malaria. It has been used in the past for severe recalcitrant acne in doses ranging from 25-50 mg/day.

The primary metabolites of dapsone are N-acetyl dapsone and dapsone hydroxylamine. The most important adverse events of dapsone result from the hydroxylamine metabolite. This compound increases oxidative stress on erythrocytes with resultant potential for dose-dependent hemolysis and methemoglobinemia. Individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency are more susceptible, as the absence of functional G6PD increases the risk of hemolysis and denaturation of hemoglobin.

It was hypothesized that a topical formulation of dapsone may be appropriate for treating acne vulgaris while minimizing systemic exposure and hematologic risk. Accordingly, a topical gel formulation of dapsone 5% was developed by Atrix Laboratories almost a decade ago for the treatment of acne vulgaris. While this product was approved by Health Canada in 2006, it has only recently been marketed in Canada.

Mechanism of Action

Dapsone has both anti-inflammatory and antimicrobial properties.1 A combination of these activities may account for its efficacy in acne. Anti-inflammatory effects include inhibition of neutrophil myeloperoxidase and eosinophil peroxidase activity, suppression of hypochlorous acid production, scavenging of reactive oxygen species, suppression of neutrophil activity, and inhibition of chemoattractant-induced signal transduction. Antimicrobial activity, similar to that of sulfones and sulfonamides, is by inhibition of bacterial dihydropterase synthase in the folic acid metabolic pathway. This mechanism is effective against microorganisms synthesizing their own folic acid. In vitro susceptibility testing has demonstrated some activity for dapsone against Propionibacterium species, including Propionibacterium acnes (P. acnes). In vivo, a 10 week randomized single-blind vehicle-controlled microbiological study demonstrated reduction in Propionibacterium counts for vehicle between 54-78%, and for topical 5% dapsone gel of 63-70% (not significant).1

Evidence for Efficacy

Two identically designed 12 week phase 3 double-blind randomized vehicle-controlled trials in acne (total N=3010) have been performed.2 The objective of these studies was to evaluate the efficacy and safety of twice daily topical dapsone 5% gel in acne vulgaris. Subjects were aged 12 years or older with facial acne, including 20-50 inflammatory lesions and 20-100 noninflammatory lesions at baseline. The primary efficacy endpoints were global success (achievement of clear or minimal on global assessment) and mean percent reduction from baseline in lesion counts. Baseline characteristics for the vehicle and active treatment groups were similar, with the majority of patients having moderate acne (58%) and a third (33%) having mild acne. At end of the study, 41% of the dapsone gel cohort achieved global success, compared with 33% of patients treated with vehicle (P>0.001). Significant reduction in non-inflammatory, inflammatory, and total lesion counts were noted in dapsone gel versus vehicle groups (32% versus 24%, 39% versus 32%, 48% versus 42%, all P>0.001, respectively).2

The efficacy of dapsone gel 5% in combination with adapalene gel 0.1%, benzoyl peroxide gel 4%, or moisturizer was evaluated in a 12 week double-blind randomized study involving 301 acne subjects.3 Dapsone gel was applied twice daily and 1 of the 3 additional treatments was applied once daily. Subjects treated with dapsone gel and adapalene showed a significantly greater improvement in non-inflammatory and total lesion count reduction compared to dapsone gel and moisturizer. The dapsoneadapalene treatment group showed a slightly higher incidence of application site burning. Overall, local adverse reactions were minimal and generally mild in severity and improved during treatment. Seven patients in the dapsone gel and benzoyl peroxide group reported temporary tan/brown residue at application sites. However, this discolored residue could be wiped away if observed. The authors suggest that, when used together, the first product should be completely absorbed prior to application of the second, without a visible layer of either product on the skin after application. Alternatively, application of these agents at different times of the day can obviate this discoloration.

Evidence for Safety

In the phase 3 studies, few patients withdrew due to side effects (6 dapsone gel, 9 vehicle). The overall incidence of adverse events was similar in both groups. The most common local intolerance events were dryness (20%), erythema (16%), and other reactions (including facial stinging, peeling, sensitivity, flaking, greasiness, photosensitivity, acne breakouts, tingling, and skin tightness). Serious adverse events were observed in 9 subjects, but they were not considered to be related to the treatment (4 dapsone gel, 5 vehicle). No significant changes in hemoglobin or other laboratory values were noted, despite 44 subjects recruited with glucose-6-phosphate dehydrogenase (G6PD) deficiency (19 dapsone gel, 25 vehicle). For all patients, the most frequently reported laboratory abnormality was elevated creatine kinase (12 dapsone gel, 11 vehicle), the majority of which were attributed to physical activity.2

A long-term safety study was performed with 486 acne patients applying dapsone gel twice daily for 12 months. Application site reactions were reported in 8.2% and were mostly mild to moderate in severity – the most common being dryness in 3%, rash 3%, sunburn 2%, burning 2%, erythema 2%, pruritus 1%, aggravation of acne 1%, and peeling 1%.4

The pharmacokinetic profile of topical dapsone gel was evaluated by reviewing data from three prospective open label studies, two phase 1 pharmacokinetic studies, and a phase 3 long-term safety study. Blood samples were drawn at various times in each trial for assessment of drug and metabolite concentrations. In various settings ranging from 2 weeks to 12 months application of dapsone gel, systemic levels (area under the curve) of dapsone and metabolites were approximately 100-fold less than those after a single dose of oral dapsone. Furthermore, the concentrations of dapsone and its metabolites achieved steady state and did not increase with prolonged treatment with dapsone gel.5

Further evaluation of hemolysis risk in subjects during dapsone gel use was performed in 64 patients with G6PD deficiency. Subjects were randomized to 12 week treatment periods of either vehicle followed by dapsone gel or dapsone gel followed by vehicle. Chemical and hematological analyses were performed, as well as levels of dapsone and metabolites, along with spontaneous reports of adverse events. Reduction in mean hemoglobin concentration of 0.32 g/dL was observed from baseline to 2 weeks during dapsone gel treatment, unaccompanied by laboratory features of hemolysis. This change was no longer apparent at 12 weeks of treatment. Proportion of subjects with 1 g/dL reduction in hemoglobin was similar between treatment groups at both week 2 and week 12 and no clinical signs or symptoms of hemolytic anemia were observed. Thus, no clinical or laboratory evidence of drug-induced hemolytic anemia in patients with G6PD deficiency was observed during treatment with dapsone 5% gel.6 The results of this study led to Health Canada and the US FDA removing the G6PD screening and monitoring requirements from the official label for this product.

Although sulfones, such as dapsone, have structural similarities to sulfonamides, the two compounds have distinct chemical properties, e.g., sulfones have both anti-inflammatory and antibacterial properties, whereas sulfonamides are antimicrobial agents. Additionally, sulphonamides have been implicated in sulfa sensitivites, but dapsone may be used in sulfonamide-allergic patients.5,7


Dapsone 5% gel is a novel option in Canada for treating acne vulgaris that may be operating via anti-inflammatory mechanisms. Efficacy in acne has been demonstrated in phase 3 and long-term studies. It has undergone rigorous evaluation for safety with no evidence of increased hemolytic risk even in G6PD-deficient patients.


  1. Center for Drug Evaluation and Research. Application number 21-794, Aczone (dapsone) gel 5%. Microbiology Review, pp 6-7.
  2. Draelos ZD, Carter E, Maloney JM, et al. Two randomized studies demonstrate the efficacy and safety of dapsone gel, 5% for the treatment of acne vulgaris. J Am Acad Dermatol. 2007 Mar;56(3):439 e1-10.
  3. Fleischer AB, Jr., Shalita A, Eichenfield LF, et al. Dapsone gel 5% in combination with adapalene gel 0.1%, benzoyl peroxide gel 4% or moisturizer for the treatment of acne vulgaris: a 12-week, randomized, double-blind study. J Drugs Dermatol. 2010 Jan;9(1):33-40.
  4. Lucky AW, Maloney JM, Roberts J, et al. Dapsone gel 5% for the treatment of acne vulgaris: safety and efficacy of long-term (1 year) treatment. J Drugs Dermatol. 2007 Oct;6(10):981-7.
  5. Thiboutot DM, Willmer J, Sharata H, et al. Pharmacokinetics of dapsone gel, 5% for the treatment of acne vulgaris. Clin Pharmacokinet. 2007;46(8):697- 712.
  6. Piette WW, Taylor S, Pariser D, et al. Hematologic safety of dapsone gel, 5%, for topical treatment of acne vulgaris. Arch Dermatol. 2008 Dec;144(12):1564-70.
  7. Webster GF. Is topical dapsone safe in glucose-6-phosphate dehydrogenasedeficient and sulfonamide-allergic patients? J Drugs Dermatol. 2010 May; 9(5):532-6.