Cotrer Gel contains two active ingredients; erythromycin (an antibiotic) that works by fighting the bacteria that cause acne, and isotretinoin (which belongs to a family of medicines called retinoids, like vitamin A), which works by helping the skin so that blocked pores are less likely. This helps prevent spots.

This is seen most commonly in patients with multiple macrocomedones and/or severe nodular acne. Such flares can be avoided or controlled by overlapping the initiation of isotretinoin therapy with oral erythromycin for up to 2 months.