mg for 6 days. Infection came back on 7/12 & 7/13. It went away on its own. Endodontist re-did root canal on 7/15. I took Metronidazole 500 mg for 7 days. Infection came 7/15, 7/17. Took last Metronidazole pill 7/23. Infection on7/23. Infection gone 1 1/2 hrs. later. Infection came 7/28, 7/31, 8/2,8/3. I have a Mitro Valvue Prolaps in my heart and wonder if waiting until 8/22 to see if root canal will be successful is okay. Should I take another antibiotic? Could the infection be in my tooth root? Why won't an antibiotic kill the infection?