Bactrim is a sulfa-based antibiotic and is not a penicillin-based medicine, according to RxList. However, a patient should discuss all allergies with a doctor to determine what drugs can and cannot be taken.
Bactrim is a combination antibiotic that is a mix of sulfamethoxazole and trimethoprim, according to RxList. It has docusate sodium, sodium benzoate, sodium starch glycolate, magnesium stearate and pregelatinized starch as inactive ingredients. Double strength tablets have 800 milligrams of sulfamethoxazole and 160 milligrams of trimethoprim. Regular Bactrim has 400 milligrams of sulfamethoxazole and 80 miligrams of trimethoprim. Bactrim is given for shigellosis and urinary tract infections for adults and for use in children's ear infection treatments.