Metronidazole comes as a tablet to take by mouth. If absolutely necessary. Metronidazole should be used with caution in patients with active or chronic severe peripheral and central nervous system diseases due to the risk of neurological aggravation. Metronidazole antibiotic is marketed by Pfizer under the trade name Flagyl, and also by various generic manufacturers, who sell it at a cheaper price. Metronidazole is one of the rare examples of a drug developed against a parasite which has since gained broad use as an antibacterial agent. Metronidazole antibiotic is marketed by Pfizer under the trade name Flagyl, and also by various generic manufacturers, who sell it at a cheaper price.