Monoclonal gammopathy is a condition where the body makes too much of a certain protein in the blood. This study is testing an antibiotic called rifaximin to see if it can help people with this condition. Antibiotics like rifaximin can help by killing bacteria in the intestines, which might reduce these abnormal proteins or cells. The study's main goal is to check how well rifaximin works after taking it for 2 weeks. They'll also see if it's safe and what changes happen in your gut bacteria.

Participants will take rifaximin by mouth three times a day for 14 days, unless they have bad side effects or the disease gets worse. After the 2-week treatment, doctors will follow up with the patient for another 8 weeks.

• The study lasts for about 10 weeks including follow-up.
• Participants must not have used antibiotics in the last 3 weeks.
• Participants should use birth control during the study and for 4 months after.

This study is open to people diagnosed with monoclonal gammopathy, and they will be placed in one of three groups based on their specific condition. If you're interested, make sure you can sign a consent form and talk to your doctor about your eligibility.