Cotrimoxazole is a combination of two antibiotics – Trimethoprim and Sulfamethoxazole. Cotrimoxazole is used to treat many kinds of bacterial infections, such as urinary tract, respiratory and skin infections.

Sulfamethoxazole is a member of the Sulfonamide family. Sulfamethoxazole and Trimethoprim work together to prevent bacteria from synthesizing folic acid, an essential B vitamin.

Cotrimoxazole is occasionally used to treat acne. Clinical research and patient reports suggest that cotrimoxazole can be a very effective treatment for some people with moderate to severe inflammatory acne (Acne Types:2-4). Clotrimoxazole is often effective for individuals who have not benefited from common anti-acne antibiotics (eg. Minocycline, Doxycycline, Clindamycin). Antibiotic susceptibility testing indicates that the acne-causing P. acnes bacteria tends to be moderately susceptible to Sulfamethoxazole and Trimethoprim, individually. The combination (Cotrimoxazole) is substantially more toxic to P. acnes bacteria.

There is a greater risk of significant side effects and allergic reactions when using Cotrimoxazole than many of the other oral antibiotics used to treat acne. In particular, Cotrimoxazole has been associated with an auto-immune reaction called Stevens Johnson syndrome, which can be life-threatening. Although the risk is small, this may explain why Cotrimoxazole is not more widely used for the treatment of acne. Individuals with a history of allergic reactions to Sulfonamide antibiotics should avoid using Cotrimoxazole.