Hi, thanks for using healthcare magic Flagyl (metronidazole) may interact with simvastatin. There are no known interactions between the flagyl and the other medications mentioned. In terms of the simvastatin and flagyl interaction- there is a possibility of peripheral neuropathy. This may or may not occur, she may not experience any problems. Peripheral neuropathy is damage to the nerves in the peripheral system (nerves not in the brain and spinal cord). It can present with weakness, abnormal sensations, twitching. The use of the probiotics would help with the resolution of the diarrhoea. She may want to avoid the use of milk products, fatty foods, gas producing foods (brussel sprouts, cabbage, beans, broccoli, cauliflower). I hope this helps