Bactrim (sulfamethoxazole and trimethoprim) allergy - timing of symptoms?

Bactrim (sulfamethoxazole and trimethoprim): Anytime but usually within 1-2 hours.

Rash.: Most common side effect or allergy to Bactrim (sulfamethoxazole and trimethoprim) is a rash. Often occurs a few days into the course of treatment, but may occur within a few hours of first dose especially if due to a true allergy to bactrim (sulfamethoxazole and trimethoprim).