Optibac probiotics for those on antibiotics is a natural supplement containing two carefully selected high quality strains of live microorganisms lactobacillus acidophilus rosell 52 and lactobacillus rhamnosus rosell 11 which are very well researched and clinically proven to survive stomach acidity and bile salts to reach the gut alive even during a course of antibiotics for those on antibiotics provides 4 billion live cultures per capsule it is free from sugars fats and flavourings