Therapeutic synergy, neutrality, and antagonism: Combination treatment in dermatology

Dermatologists frequently employ combination therapy to treat various diseases, but the evidence to support the use of such combinations is often lacking. Synergy is an appealing although somewhat ambiguous concept in medicine. Utilizing synergy allows clinicians to provide the most efficacious combination of treatments to patients, while potentially minimizing adverse effects and reducing the development of drug resistance. Definitions of synergy vary, but ultimately converge on finding a therapeutic advantage in combining treatments. Here we discuss the concept of 'therapeutic synergy', which can be defined as an increase in the efficacy of a combination of treatments in comparison to any of its individual parts alone. We review the concept of therapeutic synergy in dermatology by discussing some of the evidence regarding combination therapies utilized in the management of atopic dermatitis, acne vulgaris, psoriasis, and cutaneous lupus erythematosus. Further meaningful investigation of therapeutic synergy and its applications in dermatology should be undertaken.