Metronidazole is supposed to kill a number of parasites, I took it for 10 days or so to get rid of some parasites-B Hominis and Giardia-that I brought back from Mexico, and it worked fine, the stool tests showed they were gone but they did not kill D Fragilis unfortunately, because it's very difficult to get rid of this bug.
So don't do a parasite cleanse while you are taking metronidazole, it would be redundant and too hard on your body. Metronidazole is indeed taxing.