Rifaximin Versus No Intervention for the Treatment of IgA Monoclonal Gammopathy of Undetermined Significance

Inclusion Criteria: * Age ≥ 18 years * Ability to understand and willingness to sign a written informed consent document. Legally authorized representatives may sign and give informed consent on behalf of potential study participants * Clinical diagnosis of IgA monoclonal gammopathy of undetermined significance (MGUS) based on International Myeloma Working Group (IMWG)-2014 criteria (Rajkumar et al, Lancet Oncology, 2014) * Agree to use adequate contraception * For women of child-bearing potential: prior to study entry and for the duration of study participation * For men: prior to study entry, for the duration of study participation, and one month after completion of rifaximin administration (for men) * No antibiotic use in the preceding 2 weeks Exclusion Criteria: * Participants who are receiving other investigational agents * Pregnant women * Known hypersensitivity to rifaximin