I have been on Big 3 for 1 year now and tolerating them well. I do take a probiotic min 4 hrs apart from any antibiotic. What works for me is taking Azithromycin and Ethambutol in the morning after breakfast. Rifampin should be taken without food (at least 1 hr before or 2 hrs after a meal) so I take before I go to bed. When starting meds I was 103lbs and prescribed 500mg Azithromycin, 800mg Ethambutol & 600mg Rifampin daily . You are right to question the Ethambutol dosage, it does seem high. What I found was 15 to 25 mg per kg of weight.