Metro 400mg Tablet contains metronidazole , an antibiotic and antiprotozoal medicine that works by entering the bacterial or parasitic cells and damaging their DNA. 6. contents of the pack and other informationwhat metronidazole tablets contain:each tablet contains 200 mg, 400 mg or 500 mg of metronidazole as the active substance. Metronidazole IP 400 mg, often referred to as simply "metronidazole," is an antibiotic that belongs to the nitroimidazole class. It is designed to combat bacterial and protozoal infections by disrupting the DNA of the microorganisms, thereby inhibiting their ability to reproduce and spread. Flagyl 400 Tablet contains metronidazole, an antibiotic and antiprotozoal medicine that works by entering the bacterial or parasitic cells and damaging their DNA. This prevents the microorganisms from growing and reproducing, ultimately leading to their death and clearing the infection.