MYCOBUTIN Capsules contain the antimycobacterial agent rifabutin, which is a semisynthetic ansamycin antibiotic derived from rifamycin S. MYCOBUTIN (rifabutin) Capsules for oral administration contain 150 mg of rifabutin, USP, per capsule, along with the inactive ingredients microcrystalline cellulose, magnesium stearate, red iron oxide, silica gel, sodium lauryl sulfate, titanium dioxide, and edible white ink.