Medreef-400 contains Rifaximin (400 mg), an antibiotic primarily used to treat gastrointestinal conditions. Unlike most antibiotics, it stays mainly in the gut rather than being absorbed into the bloodstream. It is commonly prescribed for irritable bowel syndrome with diarrhea (IBS-D), traveler's diarrhea, and to prevent hepatic encephalopathy (a brain disorder caused by liver disease). It works by stopping the growth of bacteria that produce toxins in the intestines. Since it is a prescription medication, it must be taken exactly as your doctor advises. Do not stop the course early, even if symptoms improve.